1821.] Causes of Calorific Capacity, Latent Heat, %c. 261 



partial throughout the fluid. In the latter case, the solidified 

 part will exhibit a porous imperfect kind of solid, like the 

 spungy mass observed by Dr. Thomson. 



While its temperature is below the degree of solidification, if 

 any other motion be impressed on the fluid, not calculated mate- 

 rially to disturb the relative motions of the particles, the body 

 will obviously, notwithstanding this motion and the lowness of 

 its temperature, still retain its fluidity. Hence the reason of the 

 phenomena observed by Sir Charles Blagden, Phil. Trans. 1788, 

 namely, that a stirring of water cooled below 32° Fahr. does not 

 cause it to congeal; while a tremulous motion does. For by the 

 -one, the parts of the fluid merely slide over one another without, 

 perhaps, scarcely affecting the relative motions of the particles ; 

 and by the other, a succession of irregular impulses is propa- 

 gated throughout the fluid, and, consequently, to every part of 

 it, by which the relative motions of the particles cannot fail to 

 be considerably disturbed. 



Sir Charles also tells us, that opaque bodies floating in the 

 water cause it to shoot into crystals when only a few degrees 

 below the freezing point. This probably arises from the hetero- 

 geneous figure of these bodies producing a constant irregularity 

 in the motions of the aqueous particles, and thus disposing the 

 body more readily to solidify. The same philosopher likewise 

 informs us, that too sudden a cooling down of the water will 

 cause it to freeze. Now if we conceive when the temperature is 

 above the freezing point, the particles to have a latitude of 

 motion which would render their excursions wholly independent 

 of the influence of the figure of the particles, these excursions 

 in this case may be attended with a sort of rude irregularity 

 which would not affect the fluidity under such circumstances, 

 and which might be gradually constrained to within more regular 

 and uniform limits by a slow and gentle abstraction of tempera- 

 ture, so as not to destroy the fluidity ; but which, if too suddenly 

 acted on by a rapid preposterous deduction of temperature, 

 would, for the reasons we have already given, cause an instant 

 .solidification. 



A piece of ice thrown into water cooled below 32°, Blagden 

 observes, causes it immediately to shoot out into crystals. This 

 seems to be owing to some peculiarity in the arrangement or 

 figure of the icy particles, aided by the lowness of the tempera- 

 ture, which produces a dismemberment in the first instance of 

 the adjacent divisible particles, and thence by a rapid communi- 

 cation, a dismemberment of the more distant ones. The precise 

 way in which this is effected, a greater variety in the experiment 

 is necessary to determine. Many notions might indeed be 

 easily formed of the manner in which it could be done ; but as 

 experiment cannot be brought to their support, I prefer not 

 detailing them. 



We have now traced the principal phenomena attending the 



