from the Cold induced by the Evaporation (if' Water. 321 



bility, and consequently great conducting power, of that gas, 

 that the time of its attaining the temperature of the hot water 

 was scarcely two-thirds of that in the case of air; and it is as 

 natural to think that, when filled with carbonic acid, it was the 

 more sluggisli motions of that gas which rendered the time one- 

 half longer than in the case of air ; for the experiments of Mr 

 Haycraft, which are free from all such objections, shew that, 

 under equal volumes and pressures, the specific heats of the dif- 

 ferent gases are equal. If, therefore, the experiments of De- 

 sormes and Clement are so very erroneous for comparing the 

 specific heats of different gases, why should we put any confi- 

 dence in them for that of the same gas under different pressures, 

 especially when the effect of so bad a conductor as the mass of 

 the glass globe is totally overlooked ? and as for their " corro- 

 borating the law theoretically deduced by Laplace," it may be 

 suflficient to observe, that Laplace himself, shortly after framino- 

 this law, virtually repealed it by enacting a very different one 

 in its stead, which may be seen in the Mecanique Celeste, livre xii- 

 chap. 3. Both are remarkable for being quite incompatible 

 with the principles from which they profess to be deduced, 

 and are therefore to be regarded rather as laws prescribed to 

 nature than deduced from it. 



Our author is quite mistaken in his attempt to clear Dr Lard- 

 ner from teaching that the sun aids in cooling a moist body ; 

 because in his Treatise on Heat, page 241, it is distinctly stated, 

 along with a most learned rationale of the phenomenon, that 

 while the wet thermometer exposed to the sun is falling rapidly, 

 another thermometer placed near it in the shade is stationary, 

 liut though this had not been mentioned, the precisely parallel 

 case of cooling wine in the sun for want of ice, as described on 

 page 245, shews clearly that such cold was intended to be real 

 and not relative to a dry thermometer heated in the sun, as the 

 other gentleman supposes; for surely no one would seriously 

 consider wine cooled by having its temperature actually raised 

 from 66' to 74'', as this other gentleman says he found his wet 

 thermometer to be when exposed in the sun. I cannot there- 

 fore conceive how any other meaning can be attached to sucii 

 pa.ssages, than that the sun aids in the production of the cold, 

 otherwise, of what use was it to recognise the sun at all in the 



