THE THERMAL CONDUCTIVITY OF METALS. 179 
The temperature of the hot water varied not more than half a degree during an 
experiment, and the value given in each column of the preceding Table is the mean 
throughout the time. The columns of temperatures were, immediately after an 
experiment, put on a curve with time as abscissze. The effect of radiation to and 
from the calorimeter ball is fairly well marked. At the point corresponding to the 
temperature of the air in each curve there is an increase of curvature, caused by the 
fact that the radiation has changed from negative to positive. 
In order to find the flow of heat, the rise of temperature per minute was read from 
the curve ata temperature « below that of the air, and this was added to the rise 
for ° above that of the air. « varied from 0° to 4° or 5°. By this means from ten 
to fifteen readings were got, and the mean of these gave the rise at the temperature 
of the air. 
For example, for the length 6°31 centims. in the first column of Table L, the rise 
thus obtained from the curve, Diagram I, was ‘3605 in one minute. The capacity 
of the ball and of the part of the thermometer with the water in the hole was found 
to be 68°9. 
There 
68°9 x 3605 x 6:31 
~ o@ x (105)? x 87-45 x 60 
= °883 C.G:S. unit. 

This value is not corrected for the error given by the approximate formula already 
mentioned. 
Error 

~ ‘69° in this case. 
This makes the difference of temperature less by ‘7°, and when this correction is 
made we get for the conductivity ‘889 C.G.S. unit. The conductivity as calculated 
from five different lengths becomes, after the correction is made— 

Length in centims. | Conductivity. 
6°31 “889 
587 893 
5°23 ‘890 
459 ‘887 
4-015 883 


The greatest difference between these values is a little over 1 per cent. Taking 
2A 2 
