1821.] Causes of Calori/ic Capacity, Latent Heat, $>c. 20?' 



to enter into it mathematically, because at some future period it 

 may come forth connected with investigations of a much more 

 general and abstruse nature. According to bur theory of heat, 

 it is the motion or momentum of each particle of a body, and 

 not the velocity which measures the temperature of the body. 

 A particle, therefore, which is greater than another indicating 

 the same temperature, will have a less velocity in the inverse 

 proportion of its mass to the mass of the other particle. But by 

 what I have shown in p. 408 of the last volume of the Annals, 

 the tendency of one spherical particle tovvards another is, ceteris 

 paribus, as its mass ; the greater the particles, therefore, of any 

 body, the greater will be their mutual cohesive tendency. Con- 

 sequently, if other things be nearly alike, and one body be com- 

 posed of greater particles than another, the particles of that body 

 at the same temperature as the other will not only have a less 

 vibratory velocity, but will have a greater cohesive tendency ; 

 on both of which accounts the maximum range of separation of 

 the particles, or, which is the same, the expansion of the body 

 due to the temperature, will be less in the body with the greater 

 particles than in an equal volume of the body with the less parti- 

 cles. And because this is the case for any common tempera- 

 ture, it is also the case for any common increment or decrement 

 of temperature ; and, therefore, the greater the particles of any 

 body, the less will be the expansion or contraction of a given 

 volume of that body for a given increment or decrement of tem- 

 perature. Hence the expansion of mercury being less than that 

 of water for a given increase of temperature, the particles of 

 mercury are greater than those of water. 



From these considerations, we infer that bodies which are the 

 most expansible by heat have in general the greatest numeratom. 

 For as the greater expansibility is an argument of a less magni- 

 tude in the particles, so the inferiority in magnitude is an argu- 

 ment of the excess in number in a given space. This ruie, as 

 well as the preceding, is not, however, to be considered as uni- 

 versal. Philosophers will not expect where there is so great a 

 variety of formation and constitution as in the numerous bodies 

 we are acquainted with, any thing in the shape of universality. 

 That we have approached in this general inference pretty near 

 the truth may be gathered from the following observations 

 deduced from phtenomena in " Davy's Elements of Chemical 

 Philosophy," p. 77. " In general," says Sir H. " it appears 

 that the substances most expansible by heat are those which 

 have the greatest capacities. Thus gases in general have greater 

 capacities than fluids, and fluids than solids ; but the exact ratio 

 has not yet been determined." This greater capacity in its 

 implied sense evidently coincides with our greater numeratom ; 

 but it is by no means a general truth that the numeratom of gases 

 is greater than that of solids and fluids ; in fact, the contrary is 

 the case. Sir H. has here manifestly before him the capacities 



New Series, vol. ii. r 



