ON THE CONDUCTIVE POWEES OF VAEIOUS SUBSTANCES. 
849 
33. Other similar experiments were made, of which it seems unnecessary to repeat 
the details. All the results obtained have been already discussed (art. 10). I shall 
select an example of the experiments for simply determining the conductive power of 
any proposed substance. In such cases a single block (B) was generally used with an 
outer block (A) having a single cyhndrical hole. The base of the block experimented 
on (B) was usually between 4 and 6 inches in diameter. In this example the tempera- 
ture is much higher than that of boiling water. The reader Avill be able to judge 
from it the degree of approximation to stationary temperatures which I was able to 
obtain, when not availing myself of the constant temperature of boiling water. For low 
temperatures there was no difficulty in maintaining the temperatures very nearly sta- 
tionary. 
XX. Block of Sandstone. 
A=T7 feet. 
Time. 
h* 
^2- 
^2* 
i 
r. 
h m 
o 
3 30 
437-0 
79 
3 45 
448-0 
3 50 
447-5 
3 55 
447-5 
314-8 
4 0 
447-5 
4 5 
448-2 
4 10 
448-2 
320-8 
4 15 
447-8 
4 20 
447-6 
4 25 
447-1 
323-8 
4 30 
447-8 
324-6 
4 35 
447-7 
325-3 
4 40 
447-6 
326-0 
4 45 
448-1 
326-4 
4 50 
447-0 
326-3 
81-5 
4 55 
446-8 
5 0 
447-8 
326-8 
330-5 
5 5 
447-4 
5 10 
448-0 
327-3 
81-0 
f 
Continued slow oscil- 
1 
0 oU 
1 
lations through l°-5. 
/ 
O I V 
Taking the mean of all the values of from 3*' 45“ to 5** 10“ inclusive, we have 
#, = 447°'65 : and taking the mean of the values of from 4^ 40“ to 5^ 10“ inclusive, 
we have ^2=326°'5 nearly. Also taking r=8I°, we obtain 
k_ 245-5 
c — 121-15 
(•I7)=-34. 
