OF NATURAL PHILOSOPHY. 317 



as its ranks have been within the last few years. 

 This acute philosopher and profound mathe- 

 matician has developed, in a series of elaborate 

 memoirs presented to the French Institute, the 

 laws of the communication of heat through the 

 interior of solid masses, placed under the influence 

 of any external heating and cooling causes, and has 

 in particular applied his results to the conditions on 

 which the maintenance of the actual observed 

 temperature on the earth's surface depends ; to the 

 possible influence of a supposed central heat on our 

 climates ; and to the determination of the actual 

 amount of the heat, derived to us from the sun, or 

 at least that portion of it on which the difference of 

 the seasons depends. 



(353.) The principal effects of heat are the sens- 

 ations of warmth or cold consequent on its entry 

 or egress into or out of our bodies ; the dilatation it 

 causes in the dimensions of all substances in which 

 it is accumulated ; the changes of state it produces 

 in the melting of solids, and the conversion of 

 them and of liquids into vapour ; and the chemical 

 changes it performs by actual decompositions 

 effected in the intimate molecules of various sub- 

 stances, especially those of which vegetables and 

 animals are composed ; to which we may add, the 

 production of electric phenomena under certain 

 circumstances in the contact of metals, and the 

 dev elopement of electric polarity in crystallised sub- 

 stances. 



(354-.) Cold has been considered by some as a 

 positive quality, the effect of a cause antagonist to 

 that of heat; but this idea seems now (with perhaps 



