356 On th PROGRESS of HEAT 
3. In order to ftate the argument more generally, let 
A, B, C, D, &c. 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 muft 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 af- 
fume, fuppefe 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 to E; 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 C3; 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. Ir, 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 {pace 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 
