On the History of the Scientific Exploration of Fog, Dew, Rain and ...

• History of Science – Hydrometeors – Fog – Rain – Dew

DIE ERDE 139 2008 (1-2) Special Issue: Fog Research pp. 11-44

On the History of the Scientific Exploration of Fog,Dew, Rain and Other Atmospheric Water

Detlev Möller (Cottbus)

Atmospheric water, today classified as hydrometeors (fog, cloud, precipitation) and depositions(dew, frost etc.), has fascinated people since ancient times as ‘heavenly’ phenomena that wereearly recognised to be part of the water cycle. However, these phenomena were not described indetail before a first understanding of fundamental atmospheric physics and of the basic chemicalcomposition of the air had been acquired. This contribution will start with a short introduction ofthe ancient philosophic view of the atmosphere and then proceed to several early modern ap-proaches to understand water evaporation and droplet formation and to a first scientific descrip-tion of the phenomena of dew, cloud and rain. Here, for the first time in modern scientificliterature, the early approaches to chemical-meteoric water analysis are presented.

Zur Geschichte der wissenschaftlichen Erforschung von Nebel,Tau, Regen und anderem Atmosphärenwasser

With 5 Figures and 3 Tables

1. Introduction

1.1 The forms of atmosphericwater (terminology)

Atmospheric water includes physical water in allaggregate states, i.e. gaseous, liquid (in dropletform) and solid (ice particles). The historic term‘atmospheric waters’ is ‘hydrometeors’ in cur-rent terminology, i.e. meteoric water. For histor-ic reasons, dew had been considered to belong

to these “waters”, before Wells (1814) ascer-tained that dew did not result from water dropswhich fell out of the sky. The phenomena – fog,mist and clouds, precipitation (rain, snow, hail)and dew – have been described since Antiquity.A phenomenological understanding of the phys-ical (but not chemical) processes associated withhydrometeors was complete only by the end ofthe 19th century. Today the physics and thechemistry in the aerosol-cloud-precipitationchain are relatively well understood – also with

12 Detlev Möller DIE ERDE

relation to climate. However, it seems that be-cause of the huge complexity a mathematicaldescription of the processes (i.e. the parame-terisation of the chemistry and also for climatemodeling) is still under construction.

Clouds and precipitation are not only the atmos-pheric link in the global water cycle but also animportant reservoir for chemical processing andthe transportation of tracer substances. To besure, clouds are distant from the earth’s surface(with the exception of fog!) and thus not simpleto study – even nowadays. Precipitation (rain,snow and hail), in contrast, has always been eas-ier to observe by human sensors (through see-ing, feeling, smelling and tasting) and to collectfor volume estimation and analysis. Precipitationwas probably long considered a climatic precon-dition for survival by early humans, but also –with its extreme events – as catastrophic, forhousing as well as for farming. In addition, themixing of air and water with pollutants (accu-rately related to as “foreign bodies” in the oldterminology) has been known since Aristotle;the role of precipitation in cleaning the envi-ronment is wonderfully described by Evelyn(1661: 20): “It is this horrid Smoake which ob-scures our Churches and makes our Palaceslook old, which fouls our Clothes and corruptsthe Waters, so as the very Rain, and refresh-ing Dew which fall in the several Seasons, pre-cipitate this impure vapour, which, with itsblack and tenacious quality, spots and con-taminates whatever is exposed to it”.

Atmospheric waters were first studied alchemi-cally, by rain water distillation in the 17th century(see section 5). But systematic studies of de-position (precipitation chemistry) only beganwith Liebig’s discovery that plants assimilate(chemically fixed) nitrogen dissolved in rain.

Humans dealt with and were fascinated by theproperties of our atmosphere already in the an-tique era. The term atmosphere, however, derived

from Greek �� (= vapour) and ��(= sphere), was not regularly used before the be-ginning of the 19th century. Willebrord Snelius,also called Willebrord van Roijen Snell (1580-1626), a Dutch astronomer and mathematician,translated the term “damphooghde” (in German“Dunsthöhe” or “Dunstkugel”) into Latin“atmosphaera” in 1608; Guericke used “aereasphaera” (Lufthülle). In old German publicationsthe term “Dunstkreis” also was used instead of“Atmosphäre”; in addition, in the 19th century theterm “air ocean” (Luftmeer, Luftozean) was alsoused, in analogy to the sea.

In ancient times atmospheric (weather) observa-tions were closely associated with astronomy,and everything above the Earth’s surface wasnamed ‘heaven’ or ‘aether’. Already before theyear 600 BC, the Greek word ‘metéron’ (or‘metéora’) was already in use. It means “a thingin the air”. Until the end of the 18th century,��(meteors) denoted all celestial phenom-ena, aqueous, vaporous, solid and light.

The word ‘air’ is derived from Greek � and Latinaer. It is not known what the root of the Germanword “Luft” is (the term Lufft was already used inthe Middle Ages); Möller (2006) discusses thepossible relation with “Licht” (light).

The gaseous substances, which were observedin alchemical experiments, were named fumes(“Dünste”), vapours (“Dämpfe”) and airs(“Lüfte”); atmospheric air (called common air)was still regarded as a uniform chemical body.The meaning of different terms in different lan-guages (e.g. French, English and German) hasbeen changing over time; the words were usedin a slightly different sense by various natural-ists. For example, German Dunst (plural Dünste)was first used in the sense of exhalations (inmodern term: emissions) and later as a synonymfor vapour – to be more exact: for visible vapour,i.e. very small water droplets, now named haze(a word which was not used before the 19th cen-

2008/1-2 History of the Exploration of Fog, Dew, Rain and Other Atmospheric Water 13

tury). In English, the term steam is used (only)for water at boiling temperature diffusing in theatmosphere; in French and German there is noequivalent term, only in a combination like “watervapour” (see Crosland 1962 for details).

Nowadays the terms air and atmosphere arewidely used as synonyms. English dictionariesdefine atmosphere as “the mixture of gases sur-rounding the Earth and other planets” or “thewhole mass of an aeriform fluid surrounding theEarth”. From a chemical point of view it is possi-ble to say that air is the substrate with whichthe atmosphere is filled, in analogy to the hydro-sphere where water is the substrate or sub-stance. Furthermore, air is an atmospheric sus-pension containing different gaseous, liquid(water droplets) and solid (dust particles) sub-stances. Thus “air chemistry” is a more adequateterm than “atmospheric chemistry”.

1.2 The atmosphere in research history

In ancient times, the motivation to observe theatmosphere was clearly the driving force whichincreased the understanding of Nature. Thus,the first to describe a number of weather phe-nomena and the water cycle was Aristotle in his“Meteorologica”. Roman Emperors were not in-terested in the continuation of Greek doctrines,they, however, kept them. After the end of An-tiquity, around the 5th century, the occident for-got the ancient scientific heritage and replacedit by one single doctrine, the bible. Especially inthe Middle Ages, when religious belief prevailedwith the view that all “heavenly” things weregoverned by God (which, after all, was the be-lief of peoples all over the world and which ledto the idea of the creation of the existence ofspecial gods for many atmospheric phenomena),probably monks were the first to observe theweather and take records, only by personal in-terest though. In those days any meteorologi-cal (i.e., weather) observation was linked to as-

trology. The idea that the motion of the stars andplanets influenced all processes on Earth and inthe atmosphere inhibited any progress of natu-ral sciences. Only in the orient Aristotle’s doc-trine remained vital and first came to Europe inthe 12th century, probably via Sicily where fa-mous alchemistic laboratories were established.

Between the great times of the Greek philoso-phers who recognised the atmosphere only byvisual observations and reflection, generalisingit in philosophic terms, and the first instrumentalobservations, there is a gap of almost 1500 years.Agricultural aspects and the understanding ofplant growth (i.e., the beginning of commercialinterests) initiated chemical research in the 17th

century. Chemistry, first established as a scien-tific discipline at around 1650 by Robert Boyle(1627-1691), had been a non-scientific discipline(alchemy) by then. Alchemy never employed asystematic approach and because of its “secrets”no public communication existed which wouldhave been essential for scientific progress. Incontrast, physics, established as a scientific dis-cipline a long time ago, made progress, especial-ly with regard to mechanics, thanks to the im-proved manufacturing of instruments in the 16th

century. Astronomers, observing the object oftheir discipline through the atmosphere, alsobegan to discover the Earth’s atmosphere. Thereare two personalities to whom deep respect mustbe addressed for initiating the scientific revolu-tion in both the physical and chemical under-standing of atmospheric water: Isaac Newton(1643-1727), who founded the principles of clas-sical mechanics in his ‘Philosophiae NaturalisPrincipia Mathematica’ (1687), and, one hundredyears later, Antoine-Laurent de Lavoisier (1743-1794), with his revolutionary treatment of chem-istry (1789) which made it possible to developtools to analyse matter; this is why he is called“the father of modern chemistry”.

With the Age of Enlightenment in the 18th centurythe interest in natural processes generally expand-


ed. Travellers and biologists were interested indescribing the climate and its relation to cultureand biota, and in the late 1700s chemists beganto understand the transformation between solid,liquid and gaseous matter. A fundamental inter-est in biological processes, such as plant growth,nutrition, animal breathing among others, stim-ulated the study of the water cycle, the gas ex-change between plant and air (including the find-ing of fixed air, CO

2, by Joseph Black in 1754),

the mineral input from the air by Liebig (1843),and a first understanding of matter cycles byearly agricultural chemists (e.g. Knop 1868). Withthe vehement industrial development in the mid-dle of the 19th century, air pollution as a new at-mospheric aspect became the object of interestof researchers; more exactly, air pollutant im-pacts (forest decline, human health, corrosion)were the first foci of research. Already in the late19th century, some impacts could be related toindividual air pollutants (cause-receptor relation-ship, e.g. Stöckhardt 1871). The techniques tomeasure trace species, however, were still verylimited. In spite of the fact that quantitative rela-tionships were missing, legislative acts concern-ing air pollution were passed in the 19th century.Nevertheless, air pollution remained a local prob-lem until the 1960s. Then, with acid rain (despitethe fact that it had already been described inEngland in 1852 by Smith) the first regional en-vironmental problem appeared in Europe. And itwas only in the 1980s that global problems wererecognised in relation with climate change dueto the global change of the air’s chemical com-position. Localised catastrophic environmentalevents like the smog events in Los Angeles(1944) and London (1952) helped to initiate at-mospheric chemistry as a new discipline sincethe beginning of the 1950s.

We can learn from history that all kinds of per-sons were interested in the subject from a philo-sophical perspective and/or with respect to theapplication of techniques (engineering) but alsomotivated always by the specific problems (e.g.,

pollution) of their era. We also hold deep respectfor our scientific ancestors for their brilliant con-clusions, based on scientific experiments withvery simple techniques and limited quantitativemeasurements (to readers interested in more de-tails of these aspects I suggest Middleton 1965,Schneider-Carius 1955 and Gilbert 1907). Withrespect to the chemistry of hydrometeors (or ingeneral to air chemistry), however, a historicaloverview is still missing in the literature.

2. Water and Air as Elements: from Antiquityto the Middle Ages and Early Modern Times

2.1 Ancient concepts of the elements

Before the 6th century BC air was identified asemptiness. Greek natural philosophers assignedair and water to the four elements (materia pri-ma: primary matter). Thales of Milet (624-546BC) was the first who tried to answer the ques-tion of how the universe could possibly be con-ceived as made not simply “by gods and dae-mons”. He defined water as a primary matterand regarded the Earth as a disc within the end-less sea. Pythagoras (about 540-500 BC) wasprobably the first to suggest the Earth be asphere, but without explanation (only based onaesthetic considerations). Parmenides of Elea(about 540-480 BC), however, explained thespheroid Earth due to his observations of shipsfloating on the sea; he was a scholar of Xeno-phanes from Kolophon (about 570-480 BC), thefounder of eleatic philosophy. Xenophanesagain was a scholar of Anaximander from Mi-let (about 611-546 BC). With Anaximander, ascholar of Thales, and Anaximenes (from Mi-let, about 585-528 BC), the cycle of pre-Socraticphilosophers is closed. Anaximenes assumed –in contrast to Thales – air to be a primary ele-ment (root or primordial matter) which canchange its form according to density: dilutedinto fire, it may condense to wind and, by fur-ther condensation, into water and finally into


soil and rocks. This was very likely the first“poetic” description of the idea that all materialon Earth is subject to cycling, where “dilution”and “condensation” are the driving processes.

Empedocles of Acragas (495-435 BC) introducedthe four elements earth, water, air and fire, thelist was then extended by Aristotle (384-322 BC)by a fifth one, the aether (explaining the heav-enly, in Greek �� ). Aristotle asked in hisMeteorologica: “Since water is generated fromair, and air from water, why are clouds not formedin the upper air?” He explained as follows (Aris-toteles 1923: I, 9, 346b/26): “But when the heatwhich was raising it leaves it, in part dispersingto the higher region, in part quenched throughrising so far into the upper air, then the vapourcools because its heat is gone and because theplace is cold, and condenses again and turnsfrom air into water. And after the water has formedit falls down again to the earth. The exhalationof water is vapour: air condensing into water iscloud. Mist is what is left over when a cloudcondenses into water, and is therefore rather asign of fine weather than of rain; for mist mightbe called a barren cloud. So we get a circularprocess that follows the course of the sun …From the latter [clouds] there fall three bodiescondensed by cold, namely rain, snow, hail …When the water falls in small drops it is calleda drizzle; when the drops are larger it is rain …When this [vapour] cools and descends atnight it is called dew and hoar-frost.”

From his Meteorologica we know that Aristo-tle believed that weather phenomena werecaused by mutual interaction of the four ele-ments (fire, air, water, earth), and the four primecontraries: hot, cold, dry and moist. Aristotlefrequently argued against ideas which wereactually closer to the truth than his own (An-thes et al. 1975). E.g., he presented the viewsof Anaxagoras considering the cause of hailas follows (Aristoteles 1952: 81): “Some thinkthat the cause and origin of hail is this: The

cloud is thrust up into the upper atmosphere whichis colder, because the reflection of the sun’s raysfrom the earth ceases there, and upon its arrival therethe water freezes. They [Anaxagoras] think this ex-plains why hailstorms are more common in summerand in warm countries.”

The Greek philosopher Anaxagoras of Klazome-nai (500-428 BC) came to Athens as a youngman, more than 100 years before Aristotle. Ques-tioned on what he was born for he answered:“To observe sun, moon and heaven” (Diogenes1921). His philosophy is based on the Eleats andEmpedocles. With his doctrine that meteorolog-ical phenomena were caused by sun activitieshe was in contradiction to the generally prevail-ing opinion. Anaxagoras’ theory is amazinglycorrect but Aristotle wrote (Aristoteles 1923: I,12, 348a/14): “… this is just opposite to whatAnaxagoras says it is. He says that this hap-pens when the cloud has risen into the cold air,whereas we say that this happens when thecloud has descended into the warm air …”.

Aristotle, in contrast to this error, however, con-tributed many accurate explanations of atmos-pheric phenomena. The description of the wa-ter cycle (reasons for rain), as presented above,could have been taken from a modern textbook.Archimedes of Syracuse, Sicily (287-212 BC) in-directly contributed with his buoyancy princi-ple to the design of the hot-air balloon, an in-vention which added much to our knowledge ofthe vertical structure of the atmosphere in the19th and the beginning of the 20th century, andto the basis for theoretical investigation of thebuoyant rise of cumulus clouds. Theophrastus(about 372-287 BC), the successor of Aristotlein the Peripatetic school, a native of Eresus inLesbos, compiled a book on weather forecast-ing, called the “Book of Signs”. His work con-sisted of ways to predict the weather by observ-ing various weather-related indicators, such asthe halo around the moon, the appearance ofwhich is often followed by rain.


2.2 From the Middle Ages to the Age of Enlightenment

All “philosophies” of the Middle Ages were basedon ancient philosophers, new observations andconclusions were not added – in contrast, due tothe predominance of non-scientific approaches(“alchemy”) there was no progress. For example,Albertus Magnus, the most prominent German phi-losopher and theologian of the Middle Ages (1193-1280), wrote four books titled “Meteorum” fullyidentical with Aristotle’s books. Although weath-er records had been taken at different locations asearly as the 14th century, meteorology did not be-come a genuine natural science until the inventionof weather instruments; after Hellmann this iscalled the 2nd period in the history of meteorology.Aristotle’s theory survived 2000 years: dew as adeposition from the air, despite the contradictionwith his observation that “both dew and hoar-frostare found when the sky is clear and there is nowind” (Aristoteles 1923: I, 12, 348b/1).

Water remained one of the four “elements”, i.e.,indivisible bodies, and the idea prevailed that oneelement could be converted into another. All sub-stances and materials in nature were considereddifferent mixtures of these four elements. As aconsequence of this belief, all substances weretransmutable into all others and were containedin each of them. Each element had two qualities:earth: cold and dry; water: cold and wet; fire: hotand dry; air: hot and wet. In his posthumous “Or-tus medicinae i. e. initia physicae inaudita” (1652)Johann Baptist (Jan) van Helmont (1577-1644)put forward the idea that all substances, exceptair, were derived from water.

The observation that remote water (materia prima)only comes from the atmosphere (atmosphericwater) certainly promoted the experiments to getthe philosopher’s stone from it. Despite muchprogress at the beginning of the 17th century, thebelief of convertibility between air and water, andwater and soil (and vice versa) was widely accept-

ed – until the chemical composition of the air andthe structure of water was discovered by Caven-dish, Scheele, Priestley, Lavoisier and others af-ter 1770. We should not forget that solely theestimation of volume and mass has been the fun-dament of the basic understanding of chemical re-actions and physical principles since Boyle. Whileinstruments to determine mass (resp. weight) andvolume had been known for thousands of years,the new instruments (thermometer, barometer) tosupply us with the necessary data to test thephysical laws were only available to scientistssince Galileo Galilei (1564-1642). Around theyear 1600, Galileo established an apparatus todetermine the weight of the air and invented acrude thermometer..Without contact to Galilei thethermometer was invented in Holland by Cor-nelius Jacobszoon Drebbel (1572-1633) and firstused in 1612 by the physician Santorio (1561-1636), called Sanctorius of Padua (Hellmann1920). The Italian mathematician and physicistEvangilista Torricelli (1608-1647), a student ofGalilei, produced a vacuum for the first time anddiscovered the principle of the barometer in 1643.Torricelli also proposed an experiment to showthat atmospheric pressure determines the level ofa liquid (he used mercury). Torricelli’s scholarVincenzo Viviani (1622-1703) finally conductedthis experiment successfully and Blaise Pascal(1623-1662), a contemporary French scientist, car-ried out very careful measurements of the air pres-sure on Puy-de-Dôme near Clermont in France. Henoticed the decrease of pressure with altitude andconcluded that there must be a vacuum in highaltitudes. In 1667 Robert Hook (1635-1703), anassistant of Boyle’s, invented an anemometer formeasuring wind speed. In 1714 Gabriel DanielFahrenheit (1686-1736), a German glassblower andphysicist, born in Danzig and later working in Hol-land, worked on the boiling and freezing of water,and from this work he developed a temperaturescale. Horace-Bénédict de Saussure (1740-1799),a Swiss geologist and meteorologist, invented thehair hygrometer for measuring relative humidity in1780. According to Umlauft (1891) Grand Duke


Ferdinand II of Toscana (who reigned 1621-1670)invented the first hygrometer (Torricelli was hiscourt mathematician). Benedetto Castelli (1578-1643), a friend of Galilei’s, used the first rain gaugein 1639 to measure the rain depth.

It is not known which is the oldest meteorolog-ical instrument, likely the wind fane (700 BC inBabylon). The poet Terentius Barro (185-159BC) used it on his estate. But it was not untilIgnacio Denti combined several wind vaneswith a wind rose in Bologna and Florence in the1570s to show exactly the incoming wind direc-tion. A rain gauge was first used in 400 BC inIndia, and independently in Palestine (ca. 100AD), and with a network in Korea (1442) for ag-ricultural purposes (Hellmann 1920). The firstcommercially produced self-registering pluvio-meter (Latin pluvia = rain) was introduced byChristopher Wren (1632-1723) in London in 1663.

It is very likely that the first physical treatmentof rainwater was performed by the great Arabscientist Abd al-Rahman al-Khazini who workedin Merv (former Persia, now Turkmenistan) be-tween 1215 and 1230 and who was a student of(Abû‘r-Raihân Muhammad ibn Ahmad) al-Bîrûnî(937-1048) who first introduced the weighing ofstones and liquids to determine their specific weight(Durant 1950, Hall 1973). Al-Khazini is known forhis book “Kitab Mizan al-Hikma” (The book ofthe Balance of Wisdom), completed in 1121, whichhas remained a central piece of Muslim physicsever since. Al-Khazini was the first to propose thehypothesis that the gravity of bodies varies de-pending on their distances from the centre of theearth and he defined the specific weight of numer-ous substances and also that of rainwater to beexactly 1.0 g cm-3 (Szabadváry 1966).

3. Water as a Chemical Compound

The debate about who was the actual discovererof the chemical composition of water (H

2O) was

called ‘water controversy’ in 19th century. With re-spect to the discovery of the chemical compositionof water, three scientists must be regarded as candi-dates (Kopp 1869): Cavendish, who was probablythe first (in 1781) to carry out experiments to formwater by combining phlogiston and dephlogisticat-ed air (O

2), also called good, pure, vital, fire air (in

German: gute Luft, Dephlogiston, Lebensluft, reineLuft, Feuerluft etc.); Watt, who formulated the com-position of water in 1783 in a similar way to Caven-dish; and finally Lavoisier, who, in 1783, made thefirst public announcement that water consisted ofinflammable air (H

2) and dephlogisticated air (O

2).

Nowadays it is hard to understand what phlogis-ton meant. The phlogiston theory, founded byJohann Joachim Becher (1635-1682) and devel-oped further by Georg Ernst Stahl (1660-1734) –both of them German chemists –, was to some ex-tent derived from the old belief that there was a fireelement and that all combustible bodies containeda common principle (element), phlogiston (whichin Greek means “flammable” or “inflammable”),which is released in the process of combustion.Substances rich in phlogiston, such as wood, burnalmost completely; metals, which are low in phlo-giston, burn less well. The phlogiston theory cre-ated great confusion and essentially empeded theunderstanding of the chemistry of phase-transferprocesses and solid-gas reactions. Chemists spentmuch of the 18th century evaluating Stahl’s theorybefore it was finally proved to be false by AntoineLavoisier. When reading these old papers with ourpresent scientific knowledge it is often difficult, ifnot impossible, to understand what the scientistsmeant by different terms; confusion also resultsfrom attributing the same term to differentsubstances (we may only conclude that in thosedays such distinguishing was not always possible):phlogisticated air for both N

2 and H

2, acid air (Sauer-

luft in German) for both CO2 and O

2. Kopp (1869)

accepted that phlogiston was actually hydrogen.Scheele (1777) found evidence that one unit byvolume of oxygen produces one unit of carbondioxide and defined that “Feuerluft (O

2) = Phlo-


giston + fixe Luft (CO2)” which was wrong and

should have be written (in the old terms) as: car-bon = fixed air (CO

2) + phlogiston”, i.e., when

carbon is burnt, it is transformed into carbonicacid (CO

2) while releasing “phlogiston”.

Hydrogen (H2) was probably already known to Pa-

racelsus and Helmont (without using the name) inthe 16th century but was often confused with othercombustible gases. Hydrogen was produced by thetreatment of metals with acids, but any “flammableair” was called “sulphurous”. Stahl maintained thatphlogiston is exhausted by metals and combineswith the acid to a flammable substance. Cavendish(1766), however, was able to show that the flamma-ble air produced by the dissolution of iron in sul-phuric acid and of zinc in hydrochloric (muriatic) acidwas phlogiston itself and did not contain anythingof acid. Today we know that this gas is hydrogen,however, at that time, other flammable gases (pro-duced for example when organic matter is decom-posed: CO, PH

3) were hardly distinguished. Caven-

dish was the first to study this flammable air (H2) in

different mixtures with common air to investigate itsexplosion (1766). Priestley (1775) found that thisflammable air (H

2) exploded much more vehemently

when brought together with the newly discoveredpure dephlogisticated air (O

2) than with common air.

Cavendish (1784: 123) observed that after the explo-sion the inside of the glass vessel became dewy (“…that common air deposits its moisture by phlogisti-cation”). In explosions in which Cavendish (1784:130) used electric sparks he found “… liquor in theglobe …; it consisted of water united to a small quan-tity of nitrous acid”. This statement is most remark-able, it forms the first evidence of HNO

3 formation

under atmospheric conditions by lightning. SirCharles Blagden (1748-1820), English physicist andCavendish’s assistant from 1782 to 1789 reported toLavoisier about Cavendish’s experiments in 1781and, together with Pierre-Simon (Marquis) deLaplace (1749-1827), the great French mathematician,he repeated Cavendish’s experiments. He was ableto invert the experiment, i.e. he decomposed water(by directing water vapour over a red-hot iron wire)

into hydrogen and oxygen. Lavoisier (1790) estimat-ed the composition of 100 g water as 85 g oxygenand 15 g inflammable gas (hydrogen), which is rela-tively close to the correct quantities: 89 + 11.

Water chemistry, however, deals with the compo-sition of natural water (or common water, to dis-tinguish it from atmospheric water). In addition,water chemistry (now often also termed aquaticchemistry) also studies chemical reactions in wa-ter and aqueous solutions (e.g. Stumm 1990; Siggand Stumm 1996; Stumm and Morgan 1996). Thus,it is obvious to speak of rain, snow, fog, cloud ordew chemistry in the sense of analysing the chem-ical composition of the solution. This is the task ofanalytical chemistry as a subdiscipline of chemis-try which has the broad mission of understandingthe composition of all matter. Much of early chem-istry was analytical chemistry since the questionsof which elements and chemicals are present in theworld around us and what are their fundamentalnature is very much in the realm of analytical chem-istry. Before 1800, the German term “Scheidekunst”(“separation craft”) was used in place of “analyti-cal chemistry”; in Dutch, chemistry is still general-ly called “scheikunde”. Before developing rea-gents to identify substances by specific reactions,only knowledge about the features of the chemi-cals (odour, colour, crystalline structure etc.) wasused to “identify” substances (cf. Fig. 5). WithLavoisier’s modern terminology of substances(1790) and his mass conversation law, chemistsobtained the basis for chemical analysis (and syn-thesis). Carl Remigius Fresenius (1818-1897) wrotethe first textbook on analytical chemistry (1846)which is still generally valid.

4. Physics of Atmospheric Waters(Hydrometeors)

4.1 Milestones of discovery

This section deals with the milestones in the step-wise approach to explain the formation of clouds


and rain from the beginning of the 17th until theend of the 19th century. First it should be notedthat a scientific understanding of phase-transferprocesses (smelting, boiling, condensing andfreezing) was not achieved before the middle ofthe 19th century (with the development of thermo-dynamics). Black, Watt, de Saussure, Deluc andother great scientists contributed to the under-standing of the nature of water vapour, for whichdifferent terms were in use. From the early 17th

century onwards a distinction was made betweenvapours (aqueous and humid particles) and ex-halations (solid and or liquid particles but notaqueous or humid). The ancient element “fire” wasused in the sense of heat until the end of the 18th

century (Deluc 1787). Thus, vapour was first con-sidered as “little bubbles of water filled with fire”.Later this was defined as fog and cloud (particles,vesicles etc.) and “visible vapour”. In 1806, Wil-helm August Lampadius (1772-1842), professor ofchemistry in Freiberg (Saxony) still wrote (1806:118): “Das atmosphärische freye Feuer verbindetsich mit dem Wasser zu einem eigenen elastischenFluidum, dem Wasserdampf; das Feuer ist fortlei-tendes Fluidum; das Wasser wägbare Substanz[Atmospheric free fire combines with water to aspecific elastic fluid, water vapour; fire is the off-conducting fluid; water a ponderable substance]”.

The milestones are summarised as follows:

– Statement by Descartes (1637) that atmos-pheric water is not air,

– First artificial cloud/fog formation, “bubbletheory” (vesicles) by Guericke (1672),

– Cloud described as a water suspension byLe Roy (1751),

– First direct observation of (walking in) cloudsby de Saussure (1783),

– First physical theory (no water dissolutionin air) by Deluc (1787),

– First cloud classification by Lamarck (1802)and Howard (1803),

– Water condenses only on particles by Aitken(1881),

– Final evidence that clouds consist of dropletsand not vesicles by Aßmann (1885).

4.2 The 17th century:Descartes and Guericke

Recall that air and water were regarded as “ele-ments” convertible into each other since Aristo-tle. The statement that water vapour is not (atmos-pheric) air by René Descartes (1596-1650), alsoknown as Renatus Cartesius, the French philoso-pher, mathematician, scientist and writer, is remark-able as this was 15 years before the introductionof the term “gas” by van Helmont. There wasobviously a need for a new word to name and dis-tinguish the laboratory airs (i.e. gaseous sub-stances) from atmospheric (common) air. This wasproposed by van Helmont: “hunc spiritum, incog-nitum hactenus, novo nomine Gas voco [I call thisentity which hitherto has been unknown by thenew name of “gas”] (Helmont 1652).

With his book “Discours de la méthode pour bienconduire sa raison et chercher la vérité dans lessciences. Plus la dioptrique. Les Meteores. Et laGéometrie. Qui sont des essais de cette méthode”Descartes (1637) presented a nature philosophyto explain “the entire physics”. His approach isfully empirical and based on careful observation.He explains the nature of clouds by vapours ris-ing from the sea (“exhalaisons & des vapours”),their distribution (through the formation of winds)and finally their “contraction” into clouds andfogs (nuës & de la brouille). As fog he definesthe “vapours” near the earth’s surface.

The same explanation was used by Ludwig Frie-drich Kämtz (1801-1867, Kämtz 1940), professor


of physics in Halle (Germany), and by Flamma-rion. Flammarion (1873) wrote: “When it [con-densation] occurs at the level of the soil, it istermed mist. But there is no essential differencebetween a cloud and mist.” Nowadays we callmist a thin fog near the ground; even thinner mistis called ‘haze’ (atmospheric moisture or dust orsmoke that causes reduced visibility).

Descartes wrote that “expanding vapours pro-duce wind and contracting vapours produceclouds”. It seems remarkable that Descartes alsoused the terms water droplet (goutte d’eau; inLatin: gutta = drop, guttula = droplet) and iceparticles (parcelles de glace). He argued thatthe water droplets must be perfectly ball-shaped (rondes) and that they are small other-wise they would fall down as rain or snow. Inaddition, he wrote that high-altitude cloudsnever consist of water droplets but of ice parti-cles. Rain is formed when many water dropletscoalesce after collision (“… se touchent et elless’assemblent”). Principally, Descartes remainedwithin the philosophy of Aristotle, i.e. retainedthe idea of the transformation of water into airand vice versa. Descartes defined three ele-ments (éléments) or particles (parties), thosefrom fire (very fine), earth (coarse) and air (fine),corresponding to the heat, solid and liquid/gas-eous state of matter. He used the term matter(matière) as a general term and for him the par-ticles are divisible in an unlimited way. To me itappears that he was the first to clearly describethe phenomenology of the mixed-phase cloudprocesses and to state that clouds contain iceparticles also in the summer.

Some 20 years after the publication of LesMétéores, between 1650 and 1662, Otto von Gue-ricke (1602-1686), mayor of Magdeburg, invent-ed the air pump and worked on his famous ex-periments concerning the physics of the air. Inaddition, he studied the formation of clouds. Inhis famous book “Experimenta nova (ut vocan-tur) Magdeburgica de vacuo spatio” (1672), pub-

lished more than 10 years after the experiments,he stated in the first chapter of the third book(De aere ejusque origine, natura & qualitatibus[on the air, its origin, nature and properties],Guericke 1672a: 71, translated from the Germanedition, Guericke 1672b, see also Guericke1972c): “The air, according to our idea, can bedivided into steps or regions. Each kind of cloud,heavier or lighter, keeps to its own particular oneof these regions, in which its weight matches thatof the air. But if the air was compressed every-where it would be equally heavy above and be-low, so that clouds could not be formed in dif-ferent ways in different regions; but as in waterthings either sink to the bottom or float, so theclouds would either descend to the earth, or goup to the highest part of the air … Air is not anelemental substance (non est elementum) … Airis nothing else then damping (exspiratio) or smell(odor) or effluence of waters, earth and othersubstances … Air and smell once generated fromwater or other things and will never be trans-formed back to water but remains air.”

Guericke also produced clouds (nubes) and fog(nebula) by expansion of air from one flask intoanother one which had been evacuated; hewrote (in the eleventh chapter on p. 88) the fol-lowing phrase which seems to me the first sci-entific statement that cloud particles are bub-bles or vesicles (not droplets; in Latin vesica =vesica and vesicula = vesicle): “Quod tantòmagis apparet, quantò magis vitrum interne hu-miditatibus refertum est; tunc enim plures accopiosiores exurgunt bullulæ, ita ut (…) nebu-lam constituant; quæ per intromissionem ali-quid aëris … tunc nebula illa in nubes dis-pergitur. [This effect appears so much clearerthe higher the humidity in the glass flask is;then numerous and larger bubbles producingfog are formed. By running a little bit of air intothe glass … the fog dissipates into clouds].”

While later scientists argued that the water par-ticles may only exist in clouds when they


“swim”, the “bubble theory” was almost ac-cepted. However, even when the bubbles (orvesicles) are filled with common air, the cloudvesicles must be heavier than the medium inwhich they swim (Kämtz 1840). It was not untilthe end of the 19th century that the long debatewhether cloud particles are droplets or vesi-cles, started by Descartes and Guericke, wasended by Aßmann’s microscopic observations.

4.3 Concepts of the 18th century

Charles Le Roy (1726-1779), French professorfor medicine in Montpellier and Paris, used theterm “solution” to describe fog and clouds(1771). He mentioned the experiment in which iceis placed in a dry glass, which soon becomescovered with very small drops of water. The tem-perature, which we now call dew point, is called“le degré de saturation de l’air” by Le Roy.Dew, he said, forms everywhere in the atmos-phere near the ground. And, he pointed out that“dry air” on a summer day can contain morewater than very “moist air” in winter.

Jean-André Deluc (1727-1817), Swiss naturalscientist, was the first to observe clouds dur-ing his many walks in the Alps. In his famousbook “Idées sur la météorologie” (1786) he de-scribed the reasons for evaporation and theformation of “aqueous vapours”; he called hy-drometeors “gutterable water” (translated into“wässerigte Dünste”, “Wasserdünste” and“tropfbares Wasser” in the German edition). Heconcluded that the atmospheric water vapouris identical with that from boiling water. Thiscorrect conclusion (i.e. phase transition), basedon a friendly contact with James Watt (1736-1819), replaced the former hypothesis that wa-ter vapour was formed by the “dissolution ofwater in air”. He was the first to correctly de-scribe the “water-fire” relationship in the sensethat vapour is a composition of water and heator dissolution of water into vapour.

The German naturalist Christian GottliebKratzenstein (1723-1795), known for his stud-ies of electricity impacts on humans, first meas-ured the size of cloud droplets by comparingthem with a hair, in 1744 or even before (Kratzen-stein 1744); arguing that the thickness of a hairis 1/300 inch, he obtained a size of 0.00028 inch,very similar to the later estimate by Horace Béné-dict de Saussure (1740-1799), another Swissnatural scientist (mainly geologist), who pub-lished the book “Essais sur l’hygrométrie”(1783). The latter constructed and used the firsthair hygrometer which consists of a hair free ofgrease fixed to the frame at the top and to aweight at the bottom. However, he did not knowthat the measurement result represented only therelative humidity. De Saussure tried to estimatethe size of cloud droplets with a magnifier whichresulted in between 0.00022 and 0.00036 inch;assuming Prussian “Zoll” for inch, i.e. 2 3/5 cm,the size corresponds to 8 μm which comes veryclose to a mean cloud droplet we measure to-day. De Saussure distinguished between fourtypes of “vapours” (vapeurs): the “pure elasticvapour” (vapeur élastique pure) just after theevaporation of water, the “dissolved elastic va-pour” (vapeur élastique dissoute), the water va-pour proper, and finally two types of condensedwater, first the “vapour vesicles” (vapeur vé-siculaire), which he describes as very fine par-ticles (mist in modern terms), and finally “solidvapour” (vapeur concrète), likely a step in form-ing precipitation (he wrote: “When finally theelastic vapours or vesicles condense to smallsolid droplets …” ). French concret means(chemically) ‘solid’, as opposed to ‘fluid’. It ishard to understand what de Saussure means by“solid droplets” – perhaps frozen water, i.e. iceparticles? Or could it mean haze in the sense ofcondensation nuclei? Clouds and fog (cloudsat the Earth’s surface) consist of many suchvesicles (he walked and observed droplets bymagnifier). Saussure, however, remained an ad-herent of the “dissolution theory” (transforma-tion of water into air).


The understanding of cloud formation at the endof the 18th century can be described by the fol-lowing scheme:

Deluc characterised vapour as “fine water par-ticles” (in modern terms: molecules), Dunst(haze) as coarser water particles, likely identi-cal with Saussure’s “vapeur concrète” (in mod-ern terms: haze particles, i.e. atmospheric mois-ture or dust or smoke that causes reduced vis-ibility; Russell (1895: 232) presents the first ex-planation of haze as a scientific term: “This hazemay be taken to be caused by the aggregatednuclei of dust left after evaporation of the wa-ter which condensed upon them”).

4.4 Atmospheric water in the 19th century

Deluc’s theory was the most advanced in Geh-ler’s “Physikalisches Wörterbuch” (1825-45).Kämtz (1840) discusses the reason why clouddrops remain suspended in the air, even if theyare heavier than air (he still adhered to the vesi-cle theory, but inside the air and not in other –lighter – gases), and concluded that this was byascending air. In spite of a rapid development ofmeteorology to a scientific discipline at the be-ginning of the 19th century (Humboldt, Brandes,Dove) it was not before 1870 that new fundamen-tal insights into cloud formation were gained.

Paul-Jean Coulier (1824-1890), a French pharma-cist, and John Aitken (1839-1919), a Scottish phys-icist and meteorologist working in England, con-ducted the first elementary experiments and ob-servations on the role of fine airborne particles invapour condensation processes. Coulier pub-

lished his results in 1875 and Aitken published hisin 1880. They conducted almost identical experi-ments, obtained very similar results and provid-ed similar explanations: Vapours condense on solidairborne nuclei. Nevertheless, Coulier had diffi-culty explaining some of his later results by the“condensation nuclei hypothesis”; he thoughtthat this hypothesis was not generally valid.Aitken only noticed Coulier’s paper in 1881. Herepeated some of Coulier’s experiments and wasthen able to explain all of his and Coulier’s resultsby means of the “condensation nuclei hypothe-sis”, which he considered as generally valid. Thiswork led to the continuing study of heterogene-ous nucleation and the development of conden-sation nuclei counters. Aitken built the first ap-paratus to measure the number of dust and fogparticles in the atmosphere. One of his experi-ments, conducted with a self-designed apparatus,provided the first evidence of new particle forma-tion in the atmosphere. As early as 1874 (but onlypublished in 1880), Aitken had concluded thatwhen water vapour condenses in the atmosphere,it must condense on some solid particle; withoutthe presence of dust or other aerosol particles inthe air, there would be no formation of fog, cloudsor rain. Despite the fact that others had arrived atthis conclusion even earlier (see below), Aitkenis one of the founders of aerosol science; today,his name has been given to the smallest atmos-pheric aerosol particles (“Aitken nuclei”). Aitkenhad no doubt that the nuclei were from two class-es of particulates, sea-salt and the products ofcombustion (remarkably, evidence for sea-salt inthe sub-μm range in cloud condensation nuclei,CCN, was only found 100 years later).

The last question to be answered correctly in the19th century was to resolve the problem “vesicletheory versus droplet theory”. Augustus VolneyWaller (1816-1870), a British physiologist, wasthe first after de Saussure to directly observecloud droplets and concluded (by optic pheno-mena) that they consisted of drops and not ves-icles (Waller 1847). Forty years later Adolph

Water (as body: bulk) Vapour (steam; invisible) Haze (only the German Dunst

was used; visible) (Fog and) Cloud ( ice particles) Rain or snow or hail (by cloud particle collision)


Richard Aßmann (1845-1918), German meteo-rologist, known for his aspiration psychrometerand founder of aerology, first director (1905-1914) of the Royal Prussian Aeronautic Observ-atory at Lindenberg (Brandenburg), observedcloud droplets on Mount Brocken in November1884 at different levels within the cloud, usingthe best microscope available at that time(Aßmann 1885). He also concluded that afterevaporation of the droplets he was unable to seeany residuals and therefore the CCN had to besmaller than 1 µm. The most astonishing circum-stances about the vesicle theory are the fact thatthere was almost a complete absence of a theo-ry of their formation and the fact that establishedscientists like Jöns Jakob Berzelius (1779-1848)and Rudolf Julius Emanuel Clausius (1822-1888)supported the vesicle existence.

5. The Chemistry of Atmospheric Water(Hydrometeors)

5.1 Early observations andthe era of alchemy

The observation that substances other than wa-ter (so-called foreign bodies) were connected withprecipitation was known since Aristotle. Differ-ent colours and odours had been described, most-ly in connection with fog and mist. Showers ofblood, earth, sulphur, plants, frogs and variouskinds of animals as well as coloured snow can befound in the literature (first in Homer). Thesephenomena, connected with blooms, parts of in-sects, pollen and dust, were first identified by theFrench naturalist Nicolas Claude Fabri de Pei-resc (1580-1637) and later by René-Antoine Fer-chault de Réaumur (1683-1757). The Danish OleWorm (1588-1655), also called Olaus Wormius,reported that on 16th May 1646 there was a heavyshower in Copenhagen that contained dust ex-actly like sulphur. Simon Pauli the younger (1603-1680), a German physician living in Denmark,states that on 19th May 1665 a storm in Norway

brought dust which was so much like sulphur that,when thrown into fire, it produced the same smell,and that, when mixed with spirits of turpentine, itproduced a liquor with an odour just like that ofbalm of sulphur; of course the close neighbour-hood to Iceland’s volcanoes is sufficient to explainthis occurrence (reported here after Flammarion1874). In any case, these texts suggest that the per-sons must have collected rain water for “chemicalconsideration” (remember that rain collection forestimation of the rainfall amount had been imple-mented hundreds of years before). The matter (for-eign bodies) was either regarded as suspended inthe atmosphere in a state of mixture or as elements“which pervade the atmosphere in a state of solu-tion” (Prout 1834: 347). The nature of the parti-cles was found to be of vegetable origin or frommeteoric stones or aerolites, from volcanoes andsoils, but meteorites too.

Most probably the first rain water samplings (es-pecially after lightning) for “chemical” treatment(probably distillation) were carried out by alche-mist members of the Rosicrucians (Rosencreut-zer) in their quest to find the “philosopher’sstone” (Kopp 1886). Since Aristotle it was knownthat dew only appeared in calm and serene nights.Dew which had fallen from the clear sky was re-garded as matter from the sun or even from stars.Thus, alchemists treasured dew because theybelieved it to be sideric and a potential source ofthe philosopher’s stone.

Christian Ludwig Gersten (1701-1762), a Germanprofessor of mathematics in Gießen, was the firstto find out, based on observations, that dew didnot fall from the heavens but ascends from earth,especially from plants (Gersten 1733). CharlesFrançois de Cisternay du Fay (1698-1739), aFrench chemist (known for finding two kinds ofelectricity), wrote: “Glass and porcelain collectedmuch dew, while polished metal surfaces collect-ed almost none” (du Fay 1736). Also in 1736,Petrus van Musschenbroek (1692-1761), a Dutchscientist in Leiden, reported on dew observations


Fig. 1a Plate 4 from Mutus liber (1677). It shows an alchemist and his wife wringing out a cloth andcollecting (atmospheric) water in a bowl. In the background there are five clothes stretchedamong four stakes. It is likely that dew is collected here despite the fact that similar collectorswere used later for rain water sampling but with a bowl below (!) the cloths. / Platte 4 ausMutus liber (1677). Ein Alchemist wird mit seiner Frau gezeigt, welche ein Tuch auswringenund dabei (atmosphärisches) Wasser in einem Kolben sammeln. Im Hintergrund sind fünf aufjeweils vier Pflöcke gespannte Tücher zu sehen. Wahrscheinlich wurde Tau gesammelt, obwohlspäter ähnliche Sammeleinrichtungen für das Sammeln von Regenwasser genutzt wurden,wobei aber ein Gefäß unter dem Tuch angeordnet wurde.


Fig. 1b Plate 9 from Mutus liber (1677). This figure is similar to Plate 4 (Fig. 1a) in the sense of showing (different)collectors and the sampling procedure. In Plate No 9 (identical with No 12) we see the couple filling water fromthe sampling bowl into a flask. Rain is seen in the background. The wife passes the flask to Hermes who willbring it to the laboratory (?). Because (almost very similar) figures with such “samplers” were found in manyalchemistic books, we may assume that rain water had been sampled long before but nothing is known onchemical treatment because of the secrets in that field. / Platte 9 aus Mutus liber (1677). Das Bild ähnelt derPlatte 4 (Fig. 1a) bezüglich des Zeigens von (unterschiedlichen) Sammelvorrichtungen und der Probenahmeart.Auf Platte 9 (identisch mit Nr. 12) sehen wir das Paar beim Abfüllen von Wasser aus dem Sammelgefäß in einenKolben. Regen ist im Hintergrund symbolisch zu sehen. Die Frau übergibt Hermes den Kolben – der ihn wohlin das Laboratorium bringt (?). Obwohl (zumeist völlig identische) Bilder dieser Art in vielen alchemistischenBüchern gefunden werden, dürfen wir annehmen, dass Regenwasser schon lange vorher gesammelt wurde;allerdings ist wegen der Geheimhaltung nichts über dessen chemische Behandlung bekannt.


at Utrecht and confessed that “he did not un-derstand why dew collects on some surfaces farmore than on others”. He carried out many dewcollection experiments and stored a sample 24years in a flask without changes. Musschen-broek’s “Elementa Physica” (1726) played animportant part in the transmission of Isaac New-ton’s ideas on physics to Europe.

Le Roy carried out dew experiments in 1751 inParis, and Michael Hube (1737-1807), Polish roy-al secretary in Warsaw, considered dew with re-gard to the dissolution theory. Hube (1790),Deluc (1787) and later Lampadius (1793) faughtagainst this theory. Lampadius was probably thefirst to state that the temperature difference be-tween the earth and the air layer above was im-portant for dew formation (quoted after Gehler).

Rain and dew were considered as “materia pri-ma” (or “remota”). The Rosicrucians alsocalled themselves “Frères de la Rosée Cuite”(i.e. brethren of the boiled dew), the Latin wordros (in French rosée) meaning dew (Waite 1887).Hence, alchemists attributed high importance tothe dew. The sampling of dew and rain (for thatpurpose) is illustrated by beautiful figures in the“Silent Book” (“Mutus liber”) in 1677 (Fig. 1a,1b), better known as Chemica Curiosa (1702). Itis certain that the alchemists collected dew; thesame samplers were used in the 19th century(Fig. 2). The plate which follows in Mutus Liber(not shown here) shows a couple in the labora-tory distilling the water collected and samplingthe remaining “dew salt” with a spoon. It is like-ly that the alchemists found nitre (nitrate) in dewbecause Johann Lorenz von Mosheim (1693-1755) wrote (Mosheim 1726): “Dew, the mostpowerful dissolvent of gold which is to befound among natural and non-corrosive sub-stances, is nothing else but light coagulated anddigested in its own vessel during a suitableperiod, it is the true menstruum of the RedDragon, i.e. of gold, the true matter of the Phi-losophers” (quoted after Waite 1887: 6).

Nitrate (and nitrite) has been found in dew only re-cently, in quantities much higher than expected onlyfrom dry deposition. Acker et al. (2007) systemati-cally studied the formation of nitric and nitrous acidin dew and explain it by heterogeneous formationdue to the reaction of NO

2 with water surfaces (Ack-

er and Möller 2007). There is another remarkablephrase, showing us the reaction between sea saltand dew (i.e. NaCl + HNO

3, see Möller and Acker

2007): Johann Heinrich Pott (1691-1777; 1746),German pharmacist and chemist in Berlin, quotedhis compatriot Johann Heinrich Cohausen (1665-1750), physician in Münster, who utilised van Hel-mont’s belief that volatile salts (salts that had anodour or that decomposed readily when heated)constituted the vital spirit or the breath of bothanimals and plants: “Dem Meersalz von den KüstenHispaniens entzog er allen Geschmack, indem er eswährend wenigstens 40 Tagen im feinsten Tau-Geist digerierte und putrefizierte; daraus erhielt erein völlig neues Salz … von leicht bitterem Ge-schmack und von einiger Ähnlichkeit mit der ni-trosen Natur … (He deprived the sea salt of thecoasts of Hispania of all its taste [i.e. that of com-mon salt by escaping HCl] by digesting it and pu-rifying it for at least 40 days with finest spirit of dew[probably HNO

3 from dew salt] and found an en-

tire new salt … of slightly bitter taste which showedsome resemblance to nitrous nature…[i.e.NaNO

3])” (Pott 1753: 229).

True alchemists never published their findings inbooks; their secrets were passed on from the mas-ter to the student. Most authors of alchemist trea-tises are simply writers, who often were alsoknown for novels. Nevertheless, we must assumethat these persons had contact to alchemists work-ing in laboratories. E.g., Savinien Cyrano deBergerac (1619-1655), actually Hercule Saviniende Cyrano de Bergerac, a writer in Paris, de-scribed in his novel the following situation(Bergerac 1657, see Fig. 3): “Je m’estois attachétout autour de moy quantité de fioles pleines derosée et la chaleur du soleil qui les attiroit m’eslevasi haut qu’à la fin je me trouvai au dessus des plus


hautes nuées [I put around me a lot of phials fullof dew, and the heat of the sun, attracted by it,drew me to altitudes above the highest clouds]”(quoted after Canseliet 1991: 94).

George Starkey (1628-1665), who called him-self Irenaeus Philalethes, a British alchemist(Robert Boyle was a student of his) scoffs atthe use of “water which has fallen from heav-en” (Philalethes 1667; quoted after Canseliet1991: 94): “Tractate aquas vestras pluviales,

majales, salia vestra… creditis me hoc vostroturpiloquio tristitia effici! [Prepare your rain andMay water, your salts … believe me that miserycreeps over me with your blather!]”

The “dew sampler” shown in Fig. 1a may alsohave been used for rain water collection set belowa vessel or similar device for water sampling as de-scribed by Marggraf 100 years later (cf. next sec-tion). Similarly, Evelyn’s phrase “… clean linen bespread all night in any court or garden, the least

Fig. 2 Dew sampler used by Wells. From “The Dew-Drop and the Mist or, an Account of the Nature,Properties, Dangers, and use of dew and mist in various parts of the world” (1847: 28), publishedin London anonymously (115 pp.), but likely by Charles Tomlinson (1808-1897), who publishedlater (1867) a very similar title: „The Dew-Drop and the Mist: An Account of the Phenomena andProperties of Atmosphere“ (346 pp.). / Tausammler, wie ihn Wells benutzte. Aus: „The dew-dropand the mist or, an account of the nature, properties, dangers, and use of dew and mist in variousparts of the world“ (1847), S. 28, anonym publiziert in London (115 S.), wahrscheinlich aber vonCharles Tomlinson (1808-1897), der später einen ähnlichen Titel publizierte: „The Dew-Drop andthe Mist: An Account of the Phenomena and Properties of Atmosphere“ (346 S.).


infested as to appearance: but especially if it hap-pens to rain, … dust dancing upon the surface ofit …” can be interpreted as the first description ofa “deposition gauge” (Evelyn 1661: 32).

5.2 Precipitation chemistry

Sampling and treatment of precipitation was firstperformed by Ole Borch, latinised to Olaus Bor-richius, (1626-1690), Danish alchemist, in 1674:“100 pounds of snow or rain or hail water, evap-orated in a vitreous vessel, transmuted into dusty

earth, partly seemed to consist of common salt”(quoted after Kopp 1843: 255). This looks to meas the first evidence for sea salt (NaCl) in pre-cipitation. However, for Borrichius (he referredto Dickinson and even to Newton) it was theconfirmation of the ancient hypothesis of waterconvertibility (Kopp 1843). Edmund Dickinson(1624-1707), physician of King James II, intenselyinterested in alchemy and chemistry and a muchrespected person in that time, distilled water ahundred times and always found earth after evap-oration, which he interpreted as transmutation(Dickinson 1686). It is known that Newton ownedan annotated and dog-eared copy of Dickin-son’s alchemical book; he expounded his corpus-cular theory of light but also speculated on al-chemical transmutation (Newton 1704). It was notuntil 1732 that Herman(nus) Boerhaave (1668-1738), a Dutch alchemist, concluded for the firsttime that the earth remaining after the distillationof rain water originated from dust which is per-manently present in the atmosphere and depos-ited into the vessel (Boerhaave 1732).

Andreas Sigismund Marggraf (1709-1782), Germanchemist in Berlin, collected and analysed rain andsnow water for purely analytical interests between1749 and 1751 in Berlin; he also analysed differentnatural (potable) waters to check their quality(Marggraf 1753). He also found ammonium, be-cause of its odour, after repeated distillation of rainwater. Altogether, he found in rain water (by iden-tifying the crystals): nitrate (saltpetre), calcium,sodium and chloride (common salt), and organicsubstrate (“sticky and oily brown remains”). He as-sumed that its origin was from salty and earthy com-ponents. He also found the rainwater to be rotting.In snow, he found more hydrochloric acid than nitricacid, and vice versa in rain (Fig. 4). Marggraf, how-ever, also found “earth” several times, i.e. silica andlime, after distillation of pure water. Therefore, healso confirmed the transmutation idea. Boer-haave’s objection that the earth found in water wasfrom atmospheric dust was “disproved” by Marg-graf by a distillation in a hermetically closed alem-

Fig. 3 Copper plate from “L’histoire comique con-tenant les états et empires de la lune” byCyrano de Bergerac (1657) showing a manascending into the air with vials filled withdew. / Kupferplatte aus „L’histoire co-mique contenant les états et empires de lalune“ von Cyrano von Bergerac (1657), dieeinen aufsteigenden Mann zeigt, an dessenGürtel Phiolen gefüllt mit Tau hängen.


Fig. 4 Rain water chemical composition (among other natural waters) from Berlin, Marggraf 1753: 157Chemische Zusammensetzung von Regenwasser (neben anderen natürlichen Wässern) aus Berlin,Marggraf 1753: 157

bic. However, Lavoisier proved (1770), by exactweighing, that the “earth” after boiling water in a

glass vessel for a long time is due to the dissolu-tion of glass. Nevertheless, I assume that an


Year What and were Author (see references)

1814 Rain Stark

1814 Paris, hail Girardin

1824 Rain Zimmermann

1825 Bad Salzuflen, rain Brandes

1834 Freiberg, rain and snow Lampadius

1834 Rain Bohling

1842 Eastern Pomerania, snow Bertels

absorption of NH3 and CO

2 (both gases produce

different carbonates and carbamates when dis-solved in water) also occurred as a laboratory arte-fact, given the high ammonia concentration in theambient air (100 years later Smith (1879) wrote thatthe air of towns was full of ammonia).

In the 19th century, rain water sampling began af-ter Liebig’s formulation of the mineral theorywhich held that plants take up nitrogen as ammo-nia, carbon as carbonic acid and sulphur as sul-phuric acid from the air for their nutrition (mineraltheory, see Vogel 1883). Justus von Liebig (1803-1873), German chemist, is known as the “father ofthe fertilizer industry”; he is regarded as one ofthe greatest chemistry teachers ever. In 1824, atthe age of 21, with Humboldt’s recommendation,Liebig became a professor at the University ofGießen, where he established the world’s firstmajor school of chemistry. In the years 1826 and1827 Liebig collected 77 rain water samples inGießen and detected nitrate and ammonium (Lie-big 1835). Liebig (1865) wrote that contemporarystudies had shown that nitric acid was alwayscontained in rain and often more in weight thanammonium and that, as a result, nitric acid was a

permanent companion of ammonia in the air. Be-fore Liebig’s findings, there was a number of stud-ies in precipitation chemistry in the early 19th cen-tury, all from Germany, with one exception(Tab. 1). All these early rain studies were basedon evaporation. Stark (1814) found lime (Ca) inrain. Zimmermann’s analysis is remarkable (1824),he detected metals (Mn, Fe, Ni), HCl and organicmatter (“pyrrhin”) for the first time (beside NH

4+,

H2CO

3, K, Ca and Mg). In 1825, Simon Rudolph

Brandes (1795-1842), a German pharmacist (not tobe confused with the German meteorologist Hein-rich Wilhelm Brandes)found between 0.8 (in May)and 6.5 ppm (in January) total dissolved materialand identified NH

4+, NaCl, CaCl

2, CaHCO

3, CaSO

4,

MgSO4, MgCl

2, MnO, FeO, and organic matter.

The substance first identified by Zimmermann andcalled “pyrrhin” was characterised some years lat-er (1828) by Vogel as not a specific substance butas water-soluble organic matter in general. Lam-padius (1837) stated that pyrrhin was nothingelse than “Humus der Sonnnenstäubchen, vomtrockenen Lande aufgeweht” (in modern Eng-lish: “humic-like substances from atmosphericaerosol originating from soil dust resuspen-sion”). With regard to the organic matter which

Tab. 1 Early reports on precipitation sampling. If no source is given in the bibliography, cited after Ludwig1862; see also Gmelin 1852: 836-839 / Frühe Berichte über Niederschlagsmessungen. Wenn in derBibliographie keine Quelle angegeben wird, zitiert nach Ludwig 1862; s. auch Gmelin 1852: 836-839


Year Author (see references) Place

1850 Marchand Fécamp

1851-52 Barral Paris

1853 Boussingault Paris

1855 Filhol Toulouse

1850’s Pierre Caën

1852-53 Bineau Lyon

1850-52 Bobière Nantes

Brandes had found he distinguished two kinds:one soluble in water and another, “animalic”,soluble in potash. The term “organic chemis-try” was first used by Berzelius in 1806 in Swed-ish (organisk kemie; Walden 1941). Beforethat, “organic matter” was called “organised”or “animal” matter. In Germany, the first text-book on “Organische Chemie” was publishedby Gmelin in 1817. Marggraf (1753) had al-ready identified organic matter in the rain ofBerlin and called it “particules visqueuses &huileuses” (viscous and oily particles).

First quantitative estimates of rain water compo-nents were made in 1848 in Wiesbaden by Fre-senius. In the 1850s, a number of French scien-tists started rain and deposition studies (almostall because of agro-chemical interests, hence fo-cused on nitrogen, see Tab. 2).

In addition, hail studies were popular (e.g. Gi-rardin 1839) and the book (1854) by PieterHarting (1812-1885), Dutch chemist and bota-nist in Utrecht, was reviewed by an unknownauthor (1856) with the interesting finding thathailstones always contained a white opaquenucleus (often several) in the middle and airbubbles; in the melted water earthy parts (vol-

canic ash), grains of sand, ammonia, diatoms,pyrite and organic matter were found.

Robert Angus Smith (1817-1874) was a Scottishchemist who investigated numerous environmen-tal issues. He was a scholar of Liebig’s and stud-ied rain chemistry in 1848 in Manchester (Fig. 5),for the first time from an air pollution point of view.He published his findings on different kinds of rainfor the first time in 1852 (since that time the term“acid rain” has been used). He was appointed QueenVictoria’s first inspector under the Alkali Acts Ad-ministration of 1863. His famous book (Smith 1872)was the first monograph on air chemistry.

In 1897 Henriet’s book was published in Paris inthe style of a modern monograph on atmospher-ic chemistry (H. Henriet was a chemist at theMontsouri Observatory near Paris; he publishedmany papers on ozone and other air constituents).He was probably the first to use the term“chimique de l’atmosphère”. In his introductionhe emphasised the importance of air chemistrymonitoring. Rain water sampling started alongwith trace gas measurements in 1881 at the Mont-souris Observatory, in a park close to the centreof Paris (the station is known world-wide for thefirst quantitative ozone monitoring).

Tab. 2 French precipitation studies around 1850 / Niederschlagsstudien in Frankreich um 1850


Fig. 5 Residual from evaporated rain water, from Smith 1872: 382ff.: “In the rain of Manchester there isconfusion of crystals; although sulphates are prominent. I do not see crystals of common salt. Itwould appear that decomposition takes place … when sulphuric acid passes into the atmospherein towns it probably seizes part of the sodium of the common salt in the same way, and so liberateshydrochloric acid – an alkali-work continually in action.” / Rückstände von abgedampftemRegenwasser, aus Smith 1872: 382ff.: „Im Regen von Manchester befindet sich ein Gewirr vonKristallen; wobei Sulfate dominierend sind. Ich kann keine Kristalle von Kochsalz erkennen. Esscheint, dass eine Zerlegung stattgefunden hat … wenn Schwefelsäure durch die Luft der Städte ziehtund wahrscheinlich einen Teil des Natriums des Kochsalzes in derselben Weise traktiert und dabeiSalzsäure freisetzt, wie es kontinuierlich in einer Alkalifabrik abläuft.“

The first long-term rain sampling monitoringstarted in 1853 at the agricultural research site inRothamsted (Lawes et al. 1882). After 1860, anumber of long-term studies was implemented atdifferent locations (Tab. 3). Oskar Kellner (1851-1911), a German chemist, together with Liebig andHellriegel considered as a pioneer in agricultur-al chemistry and called the “father” of Japaneseagricultural chemistry, came to Japan in 1881where he conducted first precipitation chemis-try measurements from 1883 to 1885. He hadbeen an assistant of Wolff’s at Hohenheim; in

1880 he was awarded a professorship in Tokyoand stayed in Japan for 12 years. From 1893 untilhis death in 1911 he was the director of the Möck-ern experimental station in Saxony. Several rainwater monitoring stations existed in the firsthalf of the 20th century using so-called deposi-tion gauges (see, e.g., Ashworth 1933). AfterWorld War II, rain water studies from an agri-cultural point of view first started in Sweden in1947 (Egnér et al. 1949) to study nitrogen (asNH

4+ and NO

3-) and sulphur input. To my

knowledge, the last to quote Marggraf’s early


finding that nitrate is contained in rain wasTorstensson (1954) (wrongly written as “Mark-graf” and without bibliographic data).

Remarkably, scientists from many disciplines wereinterested in the chemical composition of rain andsnow water in the mid-19th century and, conse-quently, reviews on original studies can be foundin several books, e.g. a review on precipitationchemical studies (in Pierre 1859 in French, almostcompletely translated into English and publishedin Smith 1872: 232ff.). Other good summaries ofrain (and other natural) water studies were pre-sented by Liebig and Kopp (1853: 705ff., Mole-schott (1859: 387ff.) and Ludwig (1862: 1ff.).

5.3 Fog and cloud chemistry

In contrast to precipitation chemistry, it was muchmore difficult to collect water from fog or clouds,primarily because appropriate sampling tech-niques (from an analytical point of view), weremissing and due to the irregular and infrequentoccurrence of fog and the labour-intensive sam-pling on mountains. The first chemical analysesof fog water were carried out by Boussingault atLiebfrauenberg in Alsace, in Paris and in the Rhinevalley (1853-54). Boussingault found nitrate, be-tween 2 mg per l (at the mountain site) and 138mg per l (in Paris), and an ammonium concentra-tion of 10 mg per l in Paris. Unfortunately, he wasonly interested in nitrogen, from an agricultural

point of view, and therefore he did not analyse anyother substance (also in rain, snow and dew). Noother cloud studies are known from the 19th cen-tury, except for urban fog (called town fog in the19th century, see next section). Only after WorldWar II cloud studies were initiated, first in theUSA (Houghton 1955), later in Germany (Mrose1966), Russia (Petrenchuk and Drozdova 1966) andJapan (Okita 1968). Systematic studies around theworld began in the 1980s: for example in Italy (San-dro Fuzzi), California/USA (Jeff Collett, DanielJacob, Jed Waldman, William Munger, MichaelHoffmann, Volker Mohnen and others) but alsoin Germany (Hans-Walther Georgii, WolfgangJaeschke). The most extensive and so far longestcloud chemistry monitoring programme started in1992 at Mt. Brocken (Harz, Germany) where morethan 25.000 water samples based on hourly collec-tions have been analysed over the last 15 years(Acker et al. 1996). It is planned to continue this pro-gramme for another 15 years under the name of BRO-CLIM, Brocken Cloud Chemistry Climatology.

5.4 From smoke and town fog to smog(urban fog)

John Evelyn (1620-1706), an educated writer andone of the founders of the Royal Society in Lon-don (1660), wrote the first book on air pollution(Evelyn 1661: 8ff.): “… in Clouds of Smoake andSulphur, so full of Stink and Darkness … It is thishorrid Smoake which obscures our Churches, and

Germany

(13 yr) Montsouris

(10 yr)

Lincoln, Newzealand

(3 yr) Tokyo (2 yr)

Rothamsted, London

Nitrate 0.47 0.70 0.150 0.085 0.19

Ammonium 0.146 0.18 0.096 0.126 0.84

Tab. 3 First long-term precipitation chemistry monitoring (cited after Warington 1889), in ppm asnitrogen / Die erste chemische Langzeit-Niederschlagsbeobachtung (zitiert nach Warington1889), bezogen auf Stickstoff


makes our Palaces look old, which our Clothes, andcorrupts the Waters, so as the very Rain, and re-freshing Dew which fall in the several Seasons,precipitate this impure vapour, which, with its blackand tenacious quality, spots and contaminateswhatever is exposed to it. … poysoning the Aerwith so dark and thick a Fog, as I have been hardlyable to pass through it, for the extraordinary stenchand halitus it send forth;… Arsenical vapour, aswell as Sulphur, breathing sometimes from thisintemperate use of Sea-Coale… our London Fires,there results a great quantity of volatile Salts, whichbeing very sharp and dissipated by the Smoake,doth infect the Aer, and so incorporate with it, thatthe very Bodies of those corrosive particles…”

Evelyn’s remark on p. 28 concerns volatile saltsand their corrosive effects after distribution in theair and may form the first evidence for gaseous(and, consequently, dissolved) HCl in the urbanair. His expression “… traveller … sooner smellsthan sees the city ...” (Evelyn 1661: 19) gives usan idea on the air pollution level. The terms‘smoake’ and ‘clouds’ in Evelyn’s booklet (onlyonce he uses the term ‘fog’) surely mean what wenow call by the word smog, an artificial expressioncoined by Harold (Henry) Antoine des Voeux, aFrench physician living in London, honorabletreasurer of the Coal Smoke Abatement Society(formed in 1882) and later President of the NationalSmoke Abatement Society (Marsh 1947) in hispaper “Fog and Smoke” for a meeting of the Pub-lic Health Congress in 1905.

Until the end of the 20th century, when the air pol-lution problems associated with the combustionof fossil fuels seem to have been solved (still un-solved is the climate change problem due to car-bon dioxide), sulphur dioxide and soot (smoke)have been the key air pollutants for centuries. Coalhas been used in cities on a large scale since thebeginning of the Middle Ages; and this ‘coal era’has not ended yet. Remarkably, the term ‘smog’is not used in Marsh’s book “Smoke” (Marsh1947). Concerning the “relationship between fog

and smoke”, Marsh wrote that fog was a naturalphenomenon, whereas smoke, passing throughfog, could not dissipate like in non-foggy weath-er because of the absence of air currents, and the“clean natural fog gradually becomes more andmore impregnated with smoke” (this is not correctbecause smoke particles act as condensationnuclei, and thus “clean natural fog” could notpossibly have appeared in cities like London inthose years). Smoke and fog as contemporaneousphenomena were scientifically described by Ju-lius Berend Cohen (1859-1935), professor for or-ganic chemistry in Leeds who had studied chem-istry in Munich. He defined: “Town fog is mistmade white by Nature and painted any tint fromyellow to black by her children; born of the air ofparticles of pure and transparent water, it is con-taminated by man with every imaginable abomi-nation. That is town fog” (Cohen 1895: 369).

Cohen conducted laboratory experiments andconcluded: “The more dust particles there are, thethicker the fog” (Cohen 1895: 371). Carbonic acid(CO

2) and sulphurous acid (SO

2) were observed

to increase rapidly during fog, and, “… althoughI have no determinations of soot to record, the factthat it increases also is sufficiently evident,” hewrote. With these terms the acid anhydrides CO

2

and SO2 were mentioned in the literature of the 19th

century and not the acids H2CO

3 and H

2SO

3

(sometimes also named gaseous carbonic acid).Fog water particles become coated with a film ofsooty oil. Consequently, fog persists longer thanunder clean conditions. Francis Albert RolloRussell (1849-1914), a British meteorologist, usedthe expression “smoky fog” and wrote that “townfogs contain an excess of chlorides and sulphates,and about double the normal, or more, of organicmatter and ammonia salts” (Russell 1895: 234).During the last fortnight of February 1891, theweight of the fog deposit in Kew (just outsideLondon) was 0.84 g per m2 which contained42.5 % carbon, 4.8 % hydrocarbons, 4 % sulphu-ric acid, 0.8 % hydrochloric acid, 1.1 % ammonia,and 41.5 % mineral matter (Russell 1895).


The observation that fog sometimes has anodour had been reported much earlier. Lampa-dius, who still considered fog as a suspensionof vesicles which include an electric fluid, wrote:“Die Nebel zeigen zuweilen einen Geruch, der ineinigen Fällen jenem der brennbaren Luft, in an-deren aber sich dem Geruch der elektrischenMaterie nähert. Diese Erscheinung kann unsvielleicht auf einen chemischen Prozeß derWasserzerlegung bey genauerer Beobachtungführen, oder vermengen sich bloß aufsteigendeGasarten mit dem Nebel? [Fogs at times have anodour which in some cases is approximately thatof inflammable air, in other cases resembles thatof electric matter. This phenomenon may lead usto a chemical process of water decomposition ifmore precisely observed, or is it possible that thisis only a result of mixing different kinds of as-cending gases with fog?]” (Lampadius 1806: 125).

Prout (1834: 315) wrote that “fogs have beensometimes observed of a strong odour, appar-ently the result of an admixture of foreign bod-ies”. A special fog or haze, called “dry fog” (inmodern terms: stratospheric aerosol veils) wasdescribed for the years 1782 and 1783 (due tothe Laki eruption in Iceland).

6. On Dew

William Charles Wells (1757-1817), born inSouth Carolina (USA) as the son of Scottish im-migrants, became physician, philosopher andprinter. He was the first to satisfactorily explainthe phenomenon of dew. He went to England in1784 and after most decisive experiments on dewhe published his book “An Essay on Dew andSeveral Appearances Connected with it” in Lon-don in 1814. This was the first scientific descrip-tion of dew formation after a long debate, andeven now it is still generally accepted. Wellsshowed that apparently all these phenomena (in-cluding hoar-frost and mist) resulted from theeffects of heat radiation from the earth’s surface

during the absence of the sun. John Tyndall(1823-1893), the Irish physicist known for the firstexplanation of atmospheric heat in terms of thecapacities of various gases to absorb or transmitradiative heat, wrote the following very clearphrase: “Aqueous water is always diffusedthrough the atmosphere. The clearest day is notexempt from it; indeed, in the Alps, the purestskies are often the most treacherous, the bluedeepening with the amount of aqueous vapourin the air. Aqueous vapour is not visible; it is notfog; it is not cloud, it is not mist of any kind. Theseare formed of vapour which has been condensedto water; but the true vapour is an impalpable trans-parent gas. It is diffused everywhere throughoutthe atmosphere, though in very different propor-tion” (quoted from Strachan 1866: 123).

The first statement I found in the literature on thefact that dew contained traces of atmospheric ori-gin (and not alchemistic elements) besides wateris given by Lampadius (based on his experimentof 1796) who said that dew consisted of pure wa-ter and some carbonic acid (2 %) but more than inrain water (Lampadius 1806). He also wrote thatdew may contain substances emitted from plants(“Ausdünstungsmaterien”) and had thereforebeen used before as medicine – bleaching proper-ties of dew have been known for centuries – andfor the cleansing of clothes. Textiles had long beenwhitened by grass bleaching (spreading the clothupon the grass for several months), a method vir-tually monopolised by the Dutch from the time ofthe crusades to the 18th century. They developed atechnique in which the cloths were alternatelysoaked in alkaline solutions and grassed, or croft-ed – a procedure in which they are exposed to airand sunlight; the textiles were then treated with sourmilk to remove excess alkali. Today, we explain thisphenomenon by surface photo-catalytic oxidant for-mation, i.e. radicals (OH) either via HNO

2 formation

or by direct O2- electron transfers.).

Probably the first chemical study on dew wasconducted by the French chemist Jean-Sébastien-


Eugène Julia de Fontenelle (1790-1842) who, in1819, collected 4 litres of dew in the marshes ofCercle, France, and found chloride, sodium, po-tassium, sulphate, calcium and carbonate (Fon-tenelle 1823) and mentioned: “This water was in-odorous, without colour, and clean; in a shorttime it deposited small flakes of nitrogenousmatter” (quoted from Pierre 1859: 41, also inSmith 1872: 241). The first quantitative estimatesof ammonia in dew are known from Boussingault(1853) taken at Mt. Liebfrauenberg (3-50 mg per l)and from the German agricultural chemists Wolfand Knop, gathered at Möckern near Leipzig in1860 (1-6 mg per l). While Boussingault collecteddew using a sponge, Wolf and Knop collecteddew with a glass cup from grass leaves beforesunrise (Knop 1868, annex: 77f.).

Renewed interest in dew formation, its physicsand chemistry, arose after 1960 because of sev-eral aspects: first, due to dry deposition on wet-ted surfaces (Chang et al. 1967; Brimblecombeand Todd 1977), second, because of ecologicalconsiderations in the last two decades (dew assource of moisture for plants, biological crusts,insects and small animals, e.g. Jacobs et al.2000) and its potential use as potable water(Beysens et al. 2006; Muselli et al. 2006) and fi-nally from an air chemical point of view, now alsotermed interfacial chemistry (Rubio et al. 2006,Acker et al. 2007). Beysens (1995) closed the“historical cycle” to Wells (1814) with his de-scription of dew formation.

7. Conclusion

Today, an uncountable number of precipitationchemistry study sites exist, often only active forshort periods with sometimes barely more than adozen samples that are collected and analysed forwhatever purpose. The history of atmosphericwater studies, at least since the systematic moni-toring in the second half of the 19th century –which is certainly unknown to most modern “pre-

cipitation chemists” – does not only create re-spect for our scientific ancestors but may definite-ly help to avoid many scientifically meaninglessstudies of the kind that have appeared over thelast 20 years. Nevertheless, the history of explor-ing the atmospheric waters is not yet closed andis likely to remain endless. The endeavour remainsto learn from previous studies to ask the appro-priate open questions and draw the right conclu-sions for further studies.

8. Biographical Notes

Bezold, Wilhelm von (1837-1907) was professor ofmeteorology in Munich as well as director of thePrussian Meteorological Institute. His main interestas a scientist was the physics of the atmosphere andhe contributed much to the theory of electrical storms.

Boussingault, Jean Baptiste Joseph Dieudonne (1802-1887), French agricultural chemist, was the author ofTraité d’économie rurale (1844), which was remo-delled as Agronomie, chimie agricole et physiologie(5 vols., 1860-1874; 2nd ed. 1884), translated intomany languages, in German as “Die Landwirthschaftin ihren Beziehungen zur Chemie, Physik und Meteo-rologie”, Halle 1851, and supplement „Beiträge zurAgricultur-Chemie und Physiologie” (1856), withample data on ammonia and nitrate in the air.

Brandes, Heinrich Wilhelm (1777-1834), professor ofphysics at Leipzig since 1826. Founder of synopticmeteorology, published the first weather map in 1820.

Dove, Heinrich Wilhelm (1803-1879), German meteo-rologist, founder of comparative climatology. In 1845he became professor of physics in Berlin, later direc-tor of the Prussian Institute of Meteorology. It wasDove’s major contribution to meteorology “to be thefirst to find a system in weather changes”; he is alsoregarded as the “father of modern meteorology”;president of the “Gesellschaft für Erdkunde zu Ber-lin” for several periods between 1848 and 1872.

Ferrel, William (1817-1891), American mathemati-cian, teacher and later meteorologist. Among hisworks published during the last ten years of his lifewere “Popular Essays on the Movements of theAtmosphere” (1882), “Temperature of the Atmos-phere and the Earth’s Surface” (1884), “Recent


Advances in Meteorology” (1886), and “A PopularTreatise on the Winds” (1889).

Hann, Julius von (1839-1921), from 1874 to 1897professor of physical geography at the universityVienna; 1897/00 in Graz and again, until 1910, inVienna

Hellmann, Johann Georg Gustav (1854-1939), pro-fessor of meteorology at Berlin’s Friedrich-Wil-helms-Universität, 1907-1922 director of the „Preu-ßisches Meteorologisches Institut” (later: GermanWeather Service); president of the “Gesellschaft fürErdkunde zu Berlin” for several periods between1901 and 1918

Howard, Luke (1772-1864), British manufacturingchemist and amateur meteorologist

Helmholtz, Hermann Ludwig Ferdinand von (1821-1894), professor of physics, anatomy and physio-logy at Berlin, Königsberg, Bonn and Heidelberg

Knop, Wilhelm (1817-1891), German professor ofagricultural chemistry in Leipzig (1861-1882), suc-cessor to Wolff as director of the agricultural experi-mental station (1856-1866). He wrote several bookson fertilizing and agricultural chemistry. Knop (1868)mentions Dr. W. Wolf. Most certainly this is not Emilvon Wolff (1818-1896), German agricultural chemist,who was the first director of the (first German)agricultural experimental station in Leipzig-Möckern(1851-1854) and 1854-1894 professor at the Univer-sity of Hohenheim (today a part of the city ofStuttgart), but perhaps one of Knop’s assistants.

Kopp, Hermann Franz Moritz (1817-1892), Ger-man chemist, a student of Liebig’s and later profes-sor in Heidelberg, since 1843; known for his bookson the history of chemistry

Lamarck, Jean-Baptiste [Pierre Antoine de Monet,Chevalier de] (1744-1829), French biologist andmeteorologist

Ludwig, Herrmann (1819-1873), German professorof analytical chemistry in Jena

Margules, Max (1856-1920), Austrian meteorolo-gist; born in Brody (Ukraine), 1885-1906 memberof the “Zentralanstalt für Meteorologie”, workedespecially on tides, established a theory on polarfronts and air pressure waves.

Moleschott, Jakob (1822-1893), Dutch physicistand physiologist in Utrecht, Heidelberg and Rome

Prout, William (1785-1850), spent his life as apractising physician in London and occupied him-self with chemical research in biology and physics.He is known for his idea that the atomic weight ofevery element is a multiple of that of hydrogen.

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Summary: On the History of the Scientific Explora-tion of Fog, Dew, Rain and Other Atmospheric Water

In this paper the milestones in exploring clouds, fog,rain and dew in physics and chemistry from Anti-quity until the end of the 20th century have beendescribed. While a good description of the phenome-nology had been available since Aristotle, the actual

processes were not understood before the 19th cen-tury. The key in understanding the transformationof water through its different states (solid, liquid andgaseous) was the comprehension of the role of theheat exchange during evaporation and condensation.This understanding grew parallel to the understan-ding of the combustion process as a chemical reac-tion using atmospheric oxygen. This happenedbetween 1770 and 1790, with Deluc providing thebest comprehensive description in 1787. Togetherwith the understanding of the heat exchange associa-ted with phase transformation, the role of radiation(direct solar versus terrestrial) was considered, too.Dew formation was first described correctly byWells (1814). However, microphysical cloud dro-plet reflection was only explained a hundred yearslater with the finding that water may condense in theatmosphere only on condensation particles (Ait-ken), and with Aßmann closing the long debate ofdroplets versus vesicles. Cloud dynamic processesand rain formation, however, were not generallyunderstood before the 1920s; measurement plat-forms (balloons and aircrafts) become a preconditionin improving (and validating) cloud and rain theoriesbased on mathematical descriptions. Cloud physicsas a subdiscipline did not start before 1960. At thebeginning, the driving force for a better physicaldescription of the phenomena of atmospheric waterswas pure philosophic interest to understand nature;later, practical purposes became more importantwith meteorological monitoring for weather forecas-ting and climatology. Chemistry of atmospheric watersstarted in the Middle Ages with the alchemisticattempt to transmute water coming from the atmo-sphere (“heaven”). On the other hand, already at thattime (in the mid-17th century), fog and rain (and likelydew) were considered to be polluted in towns but alsoregarded as cleansing agents. The first semi-quantita-tive chemical analysis of rain and snow was conduc-ted by Marggraf in Berlin around 1750, with thepurpose to consider the hygienic quality of potentialdrinking-water. More detailed rain water analyseswere performed at the beginning of the 19th centuryfor the same reasons and in combination with theapplication of newly developed methods in analyti-cal chemistry. Liebig’s theory of plant nutrition fromair promoted a rapidly increasing number of chemicalstudies of rain and fog. Since then, agricultural inte-rests form an important base for rain water chemistry


monitoring. Air pollution in urban areas but alsoforest damages (in Germany) stimulated several stu-dies at the end of the 19th century. Deposition studies(bulk sampling) due to the smoke problem startedafter 1910. The aim to understand matter cycles, firstbetween local and regional scales, initiated precipita-tion chemistry in the 1930s which led to systematicresearch since the 1950s.

Zusammenfassung: Zur Geschichte der wissen-schaftlichen Erforschung von Nebel, Tau, Regenund anderem Atmosphärenwasser

Dieser Artikel beschreibt die wichtigsten Etappenin der Erkundung von Wolken, Nebel, Regen undTau von der Antike bis zum Ende des 20. Jahrhun-dert. Während die Phänomenologie des Atmosphä-renwassers bereits seit Aristoteles gut beschriebenwurde, verstand man die Prozesse erst im 19. Jahr-hundert. Das Verständnis über die Phasenumwand-lung des Wassers (in seiner flüssigen, gasförmigenund festen Form) wurde erst möglich, nachdem dieRolle des Wärmeaustauschs während des Verdamp-fens und Kondensierens klar wurde. Zwischen 1770und 1790, als Deluc im Jahr 1787 die bis dahinklarste Theorie vorstellte, wuchs dieses Verständ-nis zeitgleich mit dem Verstehen des Verbrennungs-prozesses als chemischer Reaktion unter Bindungvon Luftsauerstoff. Zugleich wurde mit dem Ver-ständnis des Wärmeaustausches im Zusammenhangmit dem Phasenübergang auch die solare Strahlung(sowohl die direkte als auch die terrestrische) be-trachtet. Die Taubildung wurde erstmals 1814 durchWells korrekt beschrieben. Eine mikrophysikali-sche Beschreibung der Wolkentropfen wurde je-doch erst 100 Jahre später möglich, nach der Er-kenntnis, dass Wasser in der Atmosphäre nur anKondensationskernen (Aitken) kondensieren kann.Auch wurde die lang anhaltende Diskussion, ob essich um Tropfen oder Bläschen handelt, durch Aß-mann beendet. Die dynamischen Prozesse in Wol-ken und die Regenbildung wurden jedoch prinzipiellerst in den 1920er Jahren verstanden, wobei Mess-plattformen (Ballons und Flugzeuge) eine Voraus-setzung für die Verbesserung (und Verifizierung)von auf mathematischen Modellen basierendenWolken- und Regentheorien bildeten. Die Wolken-

physik als eine Teildisziplin entwickelte sich abernicht vor 1960. Die treibende Kraft zu einer besserenphysikalischen Beschreibung des Atmosphärenwas-sers war zunächst reines philosophisches Interesseam Verständnis der Natur. Erst mit den beginnendenmeteorologischen Aufzeichnungen für Wettervor-hersage und Klimatologie nahmen praktische Erwä-gungen an Bedeutung zu. Die Chemie des Atmosphä-renwassers begann im Mittelalter mit alchemisti-schen Versuchen der Transmutation (Umwandlung)von Wasser, welches aus der Atmosphäre („demHimmel“) stammte. Andererseits hatte man bereitsin dieser Zeit (der Mitte des 17. Jahrhunderts) Nebelund Regen (und wahrscheinlich auch Tau) sowohl alsverschmutzt als auch als reinigende Agenzien inStädten beschrieben. Eine erste halbquantitativechemische Analyse von Regen und Schnee wurdedurch Marggraf um 1750 in Berlin durchgeführt, mitdem Ziel einer hygienischen Bewertung als Quellefür Trinkwasser. Mit Beginn des 19. Jahrhundertswurden genauere und umfangreichere Regenwasser-analysen, aus hygienischen Gründen aber auch derAnwendung der sich entwickelnden neuen analyti-schen Methoden, durchgeführt. Liebigs Theorie derPflanzendüngung aus der Luft führte zu einer zuneh-menden Anzahl chemischer Untersuchungen vonRegen und Nebel. Das landwirtschaftliche Interesseblieb seit dieser Zeit eine wichtige Grundlage fürniederschlagschemische Messreihen. Die Luftver-schmutzung in Städten, aber auch Waldschäden inDeutschland initiierten zahlreiche Untersuchungenzum Ende des 19. Jahrhunderts. Wegen der Rauch-frage begannen nach 1910 Depositionsuntersuchun-gen (bulk-Probenahme). Mit dem Ziel, Stoffkreis-läufe zuerst zwischen lokaler und regionaler Ebenezu verstehen, wurde die Niederschlagschemie in den1930er Jahren etabliert, was in den 1950er Jahren zusystematischer Forschung führte.

Résumé: Sur l’histoire de la recherche scientifiquedu brouillard, de la rosée, de la pluie et des autreseaux atmosphériques

Le présent article décrit les étapes les plus importan-tes dans l’exploration de nuages, brouillard, pluie etrosée de l’Antiquité jusqu’au XXe siècle. Alors quela phénoménologie de l’eau atmosphérique était déjà


bien décrite à l’Antiquité, les processus n’ont étécompris qu’au XIXe siècle. La compréhension duchangement de phases de l’eau (dans son état liquide,gazeux et solide) n’était pas possible avant que lerôle du transfert de chaleur pendant l’évaporation etla condensation soit devenu clair. Cette compréhen-sion augmentait dans la période de 1770 à 1790 lorsque l’on comprenait de plus en plus le processus dela combustion en tant que réaction chimique sousutilisation d’oxygène, quand, en 1787, Deluc en aprésenté la théorie la plus claire. En même temps,lors de la combinaison du transfert de chaleur et lechangement de phase, on avait également pris enconsidération le rayonnement solaire (direct et ter-restre). La première description correcte sur la for-mation de rosée, par Wells, date de l’année 1814.Cependant, la description microphysique des gout-tes de nuages n’a été réalisée que 100 ans plus tard,après que l’on avait découvert que l’eau dans l’at-mosphère ne peu condenser qu’avec des noyaux decondensation (Aitken). C’était Aßmann qui termi-nait finalement la longue discussion sur s’il s’agit degouttes ou de vésicules. Pourtant, les processusdynamiques dans les nuages et la formation de lapluie n’ont été compris que dans les années 1920.Avec ça, les plateformes de mesure (des ballons etdes avions) sont devenues indispensables pourl’amélioration (et la vérification) des théories denuages et de pluie basées sur des modèles mathéma-tiques. Or, la physique des nuages en tant quediscipline ne se développait pas avant 1960. Audébut, la force vive d’une meilleure description deseaux atmosphériques était l’intérêt purement philo-sophique à comprendre la nature, les aspects prati-ques n’ont gagné de l’importance qu’avec les enre-gistrements météorologiques pour les prévisions dutemps et la climatologie. La chimie des eaux atmos-phériques est née au Moyen Age avec des essaisalchimiques de la transmutation (transformation)d’eau de l’atmosphère (« du ciel »). De l’autre coté,

à cette époque-là (au milieu du XVIIe siècle) on avaitdéjà décrit le brouillard et la pluie (et, probablement,également la rosée) comme agent à la fois sale etpurifiant dans les villes. Une première analyse chi-mique semi-quantitative de pluie et de neige a étéréalisé par Marggraf en 1750 à Berlin et avait commebut l’évaluation hygiénique de l’eau potable. Desanalyses plus importantes et plus précises de l’eaupluviale ont été réalisées dès le début du XIXe siècle,non seulement pour des raisons hygiéniques, maisaussi pour l’application des nouvelles méthodesanalytiques en voie de développement. La théorie deLiebig sur la nutrition de plantes par l’air a engendréun nombre croissant d’analyses chimiques de la pluieet du brouillard. L’intérêt agricole est désormais unedes bases les plus importantes pour des séries demesure en chimie de précipitation. La pollution del’air dans les villes ainsi que le dépérissement desforêts en Allemagne ont entraîné de nombreusesrecherches vers la fin du XIXe siècle. À cause duproblème de la fumée, on a commencé des recherchesde déposition (bulk sampling) après l’année 1910.Dans le but de comprendre les circuits de matière,d’abord entre l’échelle locale et régionale, la chimiedes précipitations s’est établie dans les années 1930et est systématiquement analysée depuis 1950.

Prof. Dr. Detlev Möller, Atmospheric Chemistryand Air Pollution Control, Faculty of EnvironmentalSciences and Process Engineering, BrandenburgTechnical University, P.O. Box 10 13 44, 03013Cottbus, [email protected]

Manuskripteingang: 10.01.2008Annahme zum Druck: 28.05.2008

On the History of the Scientific Exploration of Fog, Dew, Rain and ...

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