AEROSTATICS. 227 



318. Heat diffuses itself on all sides, and passes 

 continually from bodies in which the temperature 

 is greater to those in which it is less ; and if a bo- 

 dy be placed in a medium of a temperature differ- 

 ent from its own, the momentary variations of its 

 temperature will be as the differences between the 

 temperature of the body and of the medium ; so 

 that if the times, reckoned from any instant, be 

 taken in arithmetical progression, the variations 

 of temperature in the body, and also the differ- 

 ences between its heat and the heat of the medium, 

 will decrease in geometrical progression. 



This law of the heating and cooling of bodies, was 

 first taken notice of by NEWTON, Scala Graduum 

 Caloris, Phil. Trans. (1701,) N 270. It was af- 

 terwards proved by the experiments of Professor 

 RICHMAN of St Petersburg. Novi Comment. Pe- 

 trop. torn. i. (1747, 1748,) p. 174., &c. 



It follows from it, that if D be the difference between 

 the temperature of the medium, and of the body 



. placed in it, and if be the heat lost in one second, 

 n 



then, at the end of V, %", 3", &c. the 'heats are 



D (i - D'' &c - ; and 



the decrements of heat in each second -, 



D 1\ D , IV 



IT ( n/' 7T (1 ~~ n) > &C ' ; and ' therefore > if < 



P2 be 



