THE THERMAL CONDUCTIVITY OF METALS. 175 
ture; equal to the gain by absorption in unit time when the ball is @ below the 
air temperature, we have | 
_ KA 

> Oh SL Ce ae 
and 
KA 
Q=— [(T-(—A]+2 
Therefore 
; + Q, KA, 
g a= — (TT — 2). 
It is seen by the last equation that the effect of radiation to or from the surface of 
the ball is completely eliminated since the coefficient of emission is numerically equal 
to the coefficient of absorption for the same difference of temperatures. It therefore 
fortunately does not matter how the surface of the ball becomes changed, so long as 
it remains the same during the half hour of the experiment. As a matter of fact, 
during the soldering process the surface becomes very much tarnished. 
Table I. gives a specimen experiment taken at random fiom my laboratory book. 
Fripay, 23rd March, 1894.—Pure Silver Wire (annealed). Length = 6°59 centims. 
Diameter = 202 centim. Temperature of Air = 14°3° C. 





| { 
Te II. I. II. 
Reading taken every Temperature of | Reading takenevery| Temperature of 
half-minute. hot end. | halt-minute. hot end. 
| I 
mc: aC: OE mc: 
10°3 98:2 14°75 98°3 
10°5 98:2 14:9 98°4. 
10°75 98:2 151 98°6 
10°95 98°38 15°25 98:5 
1115 98:2 15°45 98°6 
11°35 98-2 | 156 98-4: 
11°55 98:3 15°75 98-4. 
11°75 93°3 15-9 98°6 
| 11:95 98-2 16:05 98°5 
| 12:15 98°3 16:25 98°6 
12°35 98:2 16°4 98°6 
12°55 98°3 16°55 98°6 
12°75 98°5 16°7 98°6 
12-815 98°35 16°85 98°6 
31 98-4. 17:0 986 
13:3 | 98-3 17-15 98:6 
13°5 | 98-4 17:3 98°6 
13°65 | SiO 17°45 98°6 
13°85 5 98-4 17:6 98°6 
14:05 | 984 We 98°7 
14:25 98-4 17°86 | 98°6 
144 98-4 | 18:0 98°6 
14:6 98°3 | 




