32 2 Of the Propagation of Heat 



case, the temperature of the water at the bottom of" the~ 

 lake will be nearly the same all the year round ; and in 

 countries where there is any frost in winter, and particu- 

 larly in those lakes which lie near high mountains, and 

 are fed by torrents which proceed from Glaciers^ and melt- 

 ing snow, this constant temperature at the "bottom can 

 never be much above or below 41° F., whatever may be 

 the Heat to which the surface of the lake is exposed in 

 summer, or however long and intensely hot the summer 

 may be.* 



Let us now see what the consequences would have 

 been, had the condensation of water with cold followed 

 the law which obtains in regard to all other fluids. 



As the internal motion of the water could not have 

 failed to continue as long as its specific gravity contin- 

 ued to be increased by parting with Heat, ice would not 

 have begun to be formed till the whole mass of water 

 had arrived at the temperature of 32° of Fahrenheit's 

 thermometer. 



To see what an enormous quantity of Heat would be 



* In a letter from Professor Pictet, of Geneva, to the Author, of the 7th 

 July, 1797, accompanying the 36th number of the BiBLiOTHfeQUE Britannique 

 (in which an account, or rather translation, of the first Edition of this Essay is 

 published in tlie French language), there is the following paragraph : — 



" I took the liberty to throw in, as usual," (in the translation,) "some occasional 

 notes ; one of which will, I hope, deserve your attention. It points out the near 

 coincidence of the mean temperature of the bottom, observed in ten different lakes, 

 by M. de Saussure and myself, viz. 4^° R. (equal to 41 1° F.) with the tem- 

 perature where the niinimimi of volume, or niaxiinum of density, of water takes 

 place. We vainly strove to this day to explain the uniformity we observed in that 

 particular in several lakes very differently situated in many respects, but your re- 

 flections seem to me fully to resolve the problem." 



The following is the note in- the Biblioiheque Britannique, alluded to by Profes- 

 sor Pictet in the foregoing paragraph of his letter : — 



" Ce n'est pas seulement dans le lac de Geneve que M. de Saussure, notre savant 

 ami, a fait les experiences curieuses qui sont ici rappellees, et a quelques-imes des 

 quelles nous avons eu le plais'ir d'assister ; il les a repetees dans la Mediterranee, et 

 dans dix lacs qui bordent de part et d'autre la chaine des Alpes. Nous tirons de 



