184 Mechanics, Physics, and Chem~trg.

into two parts, with a report as loud as that of a pistol ; one of the pieces was thrown about twelve feet, the other struck the wall of the shop two, or three, feet distant. Of tbe whole number made, eight were broken at intervals of several days, but without any violent ex- plosion. Examined with the microscope, the steel appears distinctly radiated, or fibrous, to the depth of a line from the external surface, while the inside is granular, but without the slightest appearance of flaw, or want of actual contact of the particles at the point ruptured, previous to the explosion. The specific gravity of the bar-steel is 7.825~ that of the fractured pieces 7.850.

The cause of the fracture is, probably, the same as is observed in the glass toy called Prince Ilupert's drops, made by pouring melted glass into cold water ; the outside is suddenly contracted, while the particles in the imcrior, cooling more gradually, assttme a different erystaline form, and burst asunder as soon as the cohesion of the ex- ternal coating is destroyed.

TO TI IE C O 3 I , I I T T E I : ON p U B L I C A T I O N S OI,' 'FIIE 3OUI1NA~ OF THE FI IANIZ-LIN I N S T I T U T I ; ,

,d 7'NaJ~gular Compensalinff Pend.tdum.

The problem of a compensating pendulum, made of a si~lgle piece of metal, occupied my attention several years ago: the subject passed from my m(,mory, but was recently revived by looking over some old memoranda~a copy of one of which is subjoined. Besides other objeelions, aft impression that a~ instrument, like the one proposed, would be of too awkward a shape to be adopted in practice, ind~eed mc to lay the project aside. The principle is, however, applicable to other matters ; if', there%re, nothing of the kind has been suggested, and the idea be deemed sufficiently novel to be worth recording, you will, perhaps, give it a place in the Join'hal.

Let the distance from (3 to D, be tile required length of a penduhlm, C, bei~g the point of suspension, and D, the oscillating body ; it is re~iuired that the distance between them shall remain tl~e same under all changes of temperature. Now, instead of directly connecting C, D, by a straight rod, (with the use of which the condition premised is in- compatible,) let a triangle betbrmcd as in the figure, of a piece of iron~

_(2,

steel, or other wire, of a uniform thickness and density. It is obvious I) an increase of li~at will lengthen the sides A, B, and tend to thrust D, further from C ; but the side C, expanding at the same time,pushes the upper extremities of A, B, Wider apart, (as represented by tile dotted lines,) and, eonsequently,~if the length of C, be properly pro- portioned to A, B,--D, will remain at the same distance from C, as before. Again, suppose A, B, shortened by cold, the length of the pendulum is not e/tbeted, becausothe contraction of the side I), draws A, B, near together, and keeps D, where it was.

On Prevent ing " F o a m i n g " in S team Boilers. 155

Hence it would seem that whatever variations of temperature may take place, such a pendulum, if correctly made, would be invariable. As the compensating property depends on the figure of the rod, no adjusting apparatus would be required. In simplicity, and other qualities, it surpasses the mercu,'ial instrument of Graham, and the grid.iron of Harr ison-- that is, if the principle be found correct, and no mistakes iu the inferences drawn from it. One striking defect~ besides that of figure, is the want of stiffness, or rigidity, an important desideratu,n in a pendulum rod. The spring of the side C, might be fatal. To obviate this, in some measure, that side might be a flatbar, or the whole might be cut out of sheet metal, in which case the edges would oppose less resistance to the air. The position of the instru- ment, as shown in the figure, might be inverted--D, being made the point of suspension, and the weight placed at C.

Such is the memorandum referred to. If it be found of little worth, as regards the pendulum, it may, possibly, st!ggest, to some minds, more valuable speculation.

Nolo ~ro~'/e, ,.lultj 5, 1844. T. ~ '

A~'w 3Ielhod oJ'Preventing " I"oaming" in Steam Boilers.

Nolwithstanding tile numerous schemes already before the public, mte~Med to obviate the evils of priming, it would appear that they !lave Ilot exhausted tile remedial appliances within the compass of engil~eeri,g skill. 0ue mode of combating the evil has, within these l'few months, been patented by Mr. David Rapier, of Millwall, and another has been secured by registration, by Mr. John Allen, of Lon- doll. ~'Ir. David Napier 's mode consists in covering tim surface of the water in tile boiler with hollow metallic balls--premising, how- ever, that he does not confine himself exclusively to the use of balls, or to balls which have a less specific gravity thau water ; for other substances, even pebbles, may be employed, provided they are sup- ported in the interior of the boiler by any meehanieal means, as by wire gratings. Wood, he remarks, answers the purpose very well, and hollow glass balls would answer better, were it not that they are too fi'agile, when there is much ebullition. He, therefore, gives a preference to the metal balls, as they always tend to preserve the level, and present, at the same time, numerous and irregular inter- stiees for the steam to pass through. The effect which the pate0tee expects to be produced by these balls, is, in the first place, to still the water, so as to prevent its rising up in quantities with the steam;and, in the next place, that the surfaces of the upper tier of balls will serve to intereept the smaller particles of water, and so allow the steam to blow off eomparatively dry. Mr. Allen's mode of preventing foam- ing is different ; the apparatus employed is a metal box, perforated with numerous small holes, which is to be attached to the receiving end. of each pipe which leads from the boiler of a steam engine into the steam chest, and also to the receiving end of each pipe which leads fl'om the steam chest into the engine cylinder. Both of these plans