142 Mr. Emmett on the [Aug. 



sensation of cold; which is diametrically opposite to the 

 observed phenomena. Another objection arises from the pheno- 

 mena of the radiation of heat. Heat radiates with great 

 facility in vacuo (Davy's Elem. Chem. Philos. p. 207). Also 

 the motions of the planetary bodies demonstrate that they are 

 performed in a medium void of all resistance ; the portion of 

 space, therefore, in which they move must be a perfect vacuum, 

 yet the solar calorific rays pass through a vacuum of nearly 

 95,000,000 miles in extent before they reach the earth; it is 

 extremely diflRcult to see by what means the vibration of the 

 solar particles can affect those of the earth so as to excite upon 

 its surface the sensation of heat. It may certainly be urged that 

 the vibration of the solar matter excites undulations in an ethe- 

 rial fluid which pervades all space, and which communicates 

 similar vibrations among the particles of which terrestrial matter 

 is composed. This is certainly impossible ; for this medium, if 

 such exist, possesses so great rarity that its effects cannot be 

 rendered sensible. It is, therefore, perfectly impossible for 

 imdulations in such a medium to excite so strong vibrations in 

 dense, solid, and liquid matter as to produce in them an expan- 

 sive force which is almost infinite ; besides, it has never been 

 proved that undulations, communicated in this manner, can 

 produce any expansion, or any change of volume whatever. 

 Supposing all this possible, there remain other objections of very 

 considerable magnitude ; since the phenomena of heat arise 

 from vibratory motion, and expansion is the consequence of 

 elevation, and contraction of diminution, of temperature, in a gas 

 the extent of the vibrations of the particles must be as the 



4 / volume : when, therefore, by compression a gas is made to 



occupy a less volume, the extent of the vibrations is diminished, 

 and cold ought to result from the operation ; whereas heat is 

 actually excited. To this it may be rephed, that the motion 

 which is lost by the gaseous particles is communicated to those 

 of the sohd matter which is immediately in contact with the gas 

 so compressed, and produces in it the phenomena of heat : this 

 will be opposed by another experiment : Mix one volume of dry 

 oxygen with two of dry nitrous gas, they are reduced to 1^^ 

 volume, and heat is excited ; here there is a considerable loss of 

 vibratory motion, and which can only arise from the impact of 

 the dissimilar particles, by which they mutually destroy in part 

 each other's motion ; external matter, therefore, ought to be 

 affected with the sensation of cold. By similar reasonmg it may 

 be proved that the mixture of snow and muriate of lime should 

 excite heat ; whereas it is a powerful frigorific mixture. 



This hypothesis having been principally supported by some 

 experiments made 1)y the late Count Rumford ; and since there 

 appear several sources of fallacy in them, they will require rather 

 minute examination ; they are"^ fully described in the Philoso- 



