241 



As, agreeably to Dalton, a cavity occupied by a vapour acts as a 

 vacuum to any air which may be introduced, Dr. Hare argued, that 

 when a receiver, after being supplied with ether or water, is exhaust- 

 ed so as to remove all the air and leave nothing besides aqueous or 

 etherial vapour, the heat, acquired by air admitted, cannot be as- 

 cribed, consistently, to the condensation of the vapour. 



The facts above stated, he added, are not reconcileable with the 

 idea of De la Rive and Marcet, that the first portion of the entering 

 air is productive of cold, although a subsequent condensation is pro- 

 ductive of an opposite change. The effect upon the thermometer was 

 too rapid, and the quantity of the entering air too minute, to allow 

 it to be refrigerated by rarefaction in the first place, and yet after- 

 wards to be so much condensed as to become warm by the evolution 

 of caloric. 



Notwithstanding the experiments of Gay Lussac and of those of 

 De la Rive and Marcet, there appeared to Dr. Hare to be evidence in 

 favour of the heat being due to the space, rather than to the air which 

 it contained. 



With respect to Gay Lussac's celebrated experiment with the Tor- 

 ricellian vacuum, supposing such a vacuum to be a pre-eminently good 

 liberator of heat, as it ought in reason to be, the caloric would be ab- 

 sorbed by the mercury as rapidly as this metal could be made to en- 

 croach upon the space occupied by the calorific particles. 



Admitting that, for equal weights, the specific heat of air is seven 

 times as great as that of mercury, there could not have been a ca- 

 pacity greater than that of about 200 grains of the metal, whereas 

 a very small stratum of this metal, equal to one-fourth of an inch, 

 would, in the apparatus employed, amount to more than a pound. 



The rapidity with which a mercurial thermometer is affected by 

 the changes of temperature, in experiments like those which he had 

 been describing, showed, in Dr. Hare's opinion, that there was some- 

 . thing not yet understood respecting the transfer of heat in such cases. 

 It was hardly reconcileable with the process of conduction or circula- 

 tion, as ordinarily understood. 



In the experiments of De la Rive and Marcet, in which the enter- 

 ing air being made to impinge upon the bulb of a thermometer, was 

 productive of a fall in the thermometric column, it might be inferred, 

 he conceived, that the bulb interfered with the access of caloric from 

 the space. It was in fact the bulb upon which the air acted previous- 



