360 On the PROGRESS of HEAT 
preceding equation, will exhibit the relation between the tem- 
perature and the diftance, in the way of all others leaft fubje@ 
to mifapprehenfion. 
Lert the circle (Plate X. fig. 3.) defcribed with the radius 
AB, reprefent the globe of the earth ; and the circle defcribed 
with the radius AH an ignited mafs at the centre. Let HK, 
perpendicular to AB, be the temperature at H, the furface of 
the ignited mafs ; and let F D be the temperature at any point 
whatever, in the interior of the earth, BM reprefenting that at _ 
the furface. Then AB being =R in the preceding equation, 
AH =7, HK—H, °BM=T5 ‘AP=<%;and- F DF; thele 
two laft being variable quantities ; fince 
G— —— x= a we have, (taking AE 
= a and drawing E L parallel to AB, meeting HK 
in N, ahd FD in 0) ODxOE 2 = ARES es 
which is a given quantity. 
THEREFORE D isina rectangular hyperbola, of which thecentre 
is E, the affymptotes E G and E L, and the rectangle of the co- 
ordinates, equal to BA.AH X Sey or, which amounts 
to the fame, to KN.NE. 
Ir is evident from this, that if the fphere were indefinitely 
extended, the temperature at the point B and all other things 
remaining the fame, the temperature at its fuperfices would not 
be lefs than A E, or than the quantity Aro 
THE 
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