ON THE CONDUCTIVE POWEES OF VAEIOUS SUBSTANCES. 
825 
4— r), 
&c. 
&c. 
w— 1 
• • (y-) 
=|-(^w— r)A„; 
and adding, we have 
,-^,.=^(r-.){^+^+ . . . +'^+i+i+ . . . +i} . 
when, writing t^~r — — r) for — 4”^), 
A: ' A:j 
=(r-r){l + 2fj')+2(| 
<,-r=(r-r)n+^^+^'...+£^=+£+£ +£ 
— T = 
1+2 
h+T 
+ 2^ 
Tlie value of tf' — T being thus determined, the successive equations of (y.) will deter- 
mine t^i t'l, t'-i 
For the (r-l-l)th stratum we have 
-g=fw>-^) 
P. 
'k. 
t,-T 
rxi+Hf)’ 
1+2 
( 1 -) 
which gives the rate of decrease of temperature in the (r-j-l)th stratum in ascending. 
Integrating this equation, we have 
p — T 
1+2 
+ ^<f 
.2, 
whence, substituting for ^ is determined for any point in the (r-|-l)th stratum. 
14. Let us now suppose that we have, in another locality, another system of super- 
imposed strata similar to the above, in which the quantities^ k h &c. are designated by 
p' J<! h’ &c., and for which and r are the same as in the former system. Then shall 
