35 6 On the PROGRESS of HEAT 



3. In order to ftate the argument more generally, let 

 A, B, C, D, &x. be a feries of contiguous bodies ; or let them be 

 parts of the fame body ; and let us fuppofe that A receives, 

 from fome caufe, into the nature of which we are not here to 

 inquire, a conftant and uniform fupply of heat. It is plain, 

 that heat will flow continually from A to B, from B to C, &c. ; 

 and in order that this may take place, A mull be hotter than B, 

 B than C, and fo on ; fo that no uniform diftribution of heat 

 can ever take place. The ftate, however, to which the fyftem 

 will tend, and at which, after a certain time, it muft arrive, is 

 one in which the momentary increafe of the heat of each body 

 is juft equal to its momentary decreafe ; fo that the temperature 

 of each individual body becomes fixed, all thefe temperatures 

 together forming a feries decreafing from A downwards. To 

 be convinced that this is the ftate which the fyftem muft a£ 

 fume, fuppofe any body D, by fome means or other, to get 

 more heat than that which is required to make the portion of 

 heat which it receives every moment from C, juft equal to that 

 which it gives out every moment toE; as its excefs of tempe- 

 rature above E is increafed, it will give out more heat to E, 

 and as the excefs of the temperature of C above that of D is 

 diminifhed, D will receive lefs heat from C ; therefore, for 

 both reafons, D muft become colder, and there will be no 

 ftop to the reduction of its temperature, till the increments 

 and decrements become equal as before. 



4. If, therefore, heat be communicated to a folid mafs, 

 like the earth, from fome fource or refervoir in its interior, it 

 muft go off from the centre on all fides, toward the circumfer- 

 ence. On arriving at the circumference, if it were hindered 

 from proceeding farther, and if fpace or vacuity prefented to 

 heat an impenetrable barrier, then an accumulation of it 

 at the furface, and at laft a uniform diftribution of it through 

 the whole mafs, would inevitably be the confequence. But if 



heat 



