Mr. Henry on tie MateriaTity of Heat, 4^. 



ihal contained in furrounding bodies. 2dly, The fcale of 

 cxpanfion is wholly arbitrary, commencing far from the" 

 abfoliUe privation of heat, and fallino; far fliort of its ma.\i- 

 nuim. 3d!y, The caloric latent in bodies, or chemically' 

 combined with them, has no efietSt on the thermometer. 

 4th!v, The experiments of Dr. Crawford, though fufficieiil' 

 to fiiow that the cxpanfion of the mercury of the thermo- 

 meter beat-3 a ratio to the aftiuil increments of heat in any 

 temperature between the boiling and freezing points of wa- 

 ter, by no means prove that tliis proportion holds urilver- 

 fally. _ . . . ■ 



Equal weights of heterogeneous bodies, it is prefumed, 

 contain unequal quantities of caloric; and the ratio otthelcf' 

 quantities is appro.x'imated in the following manner: 



Equal weights of the fame body, at differerit tetripera^'. 

 tures, give, on admixture, the arithmetical mean; but equal' 

 weights of different bodies, at different tcmpcrat-.ires, afford a' 

 temperature wdiich varies confiderably from the mean. Thus' 

 a pound of water at ico% and a pound at 200', give' the' 

 temperature of 150°; but a pound of water at 200", and'" 

 a pound of mercury at 100% afford, not the mean, but a' 

 temperature confiderably higher. Hence it follows, that a' 

 pouad of mercury has not the power of fixing and retalning- 

 io much caloric as a pound of water; and the fixation of 

 more heat by the water than by the mercury, is afcribed to' 

 the fuperior energy of a power inherent in both, and termed' 

 capacity for caloric. 



From an extenfive feries of experiments Dr. Crawford in- 

 fers, that the capacities of bodices are permanent fo long 4s 

 they retain their form. Thus, the capacity of Avater has to 

 that ofr^ercurv the ratio of 28 to i, at any temperature be- 

 tween 3 I, and 212°. The dif!'erence of capacities of bodies,'' 

 it is infevi ;d, therefore, would continue the fame down to the' 

 abfolute ptivation of temperature. Imagine, then, two bodits 

 at this point of privation : they may fiill contain unequal quan- 

 tities of cainbined caloric; for, when chemically combined^ ca- 

 loric does not produce temperature. On Dr. Crawford's hypo- 

 thelis thcAi comparative quantities of combined caloric in the' 

 two bodies may be learned by obferving the ratio of tempe- 

 rature produced by the addition to each of fimilar quantities 

 of heat. This fuppofition, however, is manifertly gratuitous; 

 and the contrary might be maintained with equal or greater 

 probability; for it may be fuppofed that at this affumed ne- 

 gation of temperature one bodv renders latent more caloric 

 than another, becaiife it artually contains lefs, as certain dry 

 tiilts attraA: nv)re water from the atmofphere than others'^ 

 'Vol.. XV. No. ^7. JC containing 



