498 
MR. C. H. LEES ON THE THERMAL CONDUCTIVITIES 
either of which equations determines k, the conductivity of the disc, if its approximate 
value is substituted in the terms involving £ 3 . The value of h used is that for a 
• 7)1 l 
painted surface, at the mean temperature of the disc, and the value of t z is given 
with sufficient accuracy for the above substitution by the equation 
4L rt*= *00056 
qk 
A g —A 
Q 
Observations * 
I Transparent Isotropic Bodies. —-The temperatures given are the means of 
three experiments. 
Crown Glass Disc, 193 cm. chain., -169 cm. thick. Air, 16 0- 2 C. 
Cool bar. 
Hot bar. 
v l 8'58 Aj 8’83 
v 3 4-20 Q x ’1365 
. % _ '1365 x -169 x 1-001 _ .qq246 
v x 18-44 A 3 18-25 
v 2 26-54 Q, -1336 
h _-1336 x "169 x 1‘001 _ , nn0/t1 
1 18’25 — S’83 x 1'003 
18-25 X 1-003 — 8-83 
k mean = -00244. 
Flint Glass Disc, 1'93 cm. diam., -177 cm. thick. Air, 16°'6 C. 
Cool bar. 
Hot bar. 
7'60 Aj 7'83 
Vo 3 54 Q : -1254 
. 7 . -1254 x -177 x 1-002 _ , nn9n o 
19-02 Ao 18-84 
r 2 26'80 Q 3 "1246 
j - _-1246 x -177 x 1-002 _. m]po 
1 18-84 — 7-83 x 1-006 
- 18-84 x 1-006 - 7-83 
k mean = ’00201. 
Bock Salt Disc, D95 cm. diam., *83 cm. thick. Air, 15 o, 0 C. 
Cool bar. 
Hot bar. 
9-24 Ai 9-50 
v 2 4-61 Qi 1457 
k — C Q 8) ’14u 7 x 83 x rOOo _ 
18-47 Ao 18 "22 
v 2 27-31 Qo -1515 
/■ — p98) ’1515 x -83 x 1"005 _ .njgg 
1 1 } 18 22 - 9-50 x L014 ^ 
* " { } 18-22 x 1-014 - 9-50 
k mean = ’0138. 
* The results are collected in a table on page 506. 
