IMPARTED TO A VACUUM BY HOT CONDUCTOPuS. 
We now come to the application of the theoretical formula 
C/eS .. ^ 
^ 271177 
to the reduction ot these results. This equation may be written as before 
539 
y = logioC - 1 logio^ = « + h^oc,, 
<x> 
24 
bb 
o 
7.. 3 
ci , 
g 2 
to 
o 
o 
CD 
O 
CO 
wheie Xq 6^ ^,6 being the absolute temperature. To test the theory, values of y 
have been jdotted against values of 0-^ X 10^ in the following curve (fig. 21). 
It will be seen that all the points fall very nearly on a straight line except the first 
two. They are all, however, fairly accu¬ 
rately represented by the dotted curve 
shown. As the two lowest points corre¬ 
spond to a low temperature, it is possible 
that some other effect is coming in here 
which would account for their deviation 
from rectilinearity. 
In calculating the value of h [ = <P/1I) we 
may either confine our attention to the 
straight part of curve 4, and neglect the 
two first observations, or we may take the 
average over the whole range of the experi¬ 
ments. The two values differ by about 
24 per cent. ; if we take the mean we find 
h = S'16 X lOf This gives, for the dis¬ 
continuity of potential at the surface, the 
A 
V 
A 
\\ 
\ N 
\ 
''t 
•v 
V 
'\Z 13 
15 16 17 
Scale of 0"xio^ 
18 19 20 
Fig. 21. 
value 2-63 volts, and would therefore give 1-47 volt as the difference of its values for 
sodium and platinum. 
The above value of the difference, which is approximately equal to the contact 
electromotive force for sodium and platinum, forms a strong confirmation of the 
theory; but when we come to calculate 7i, the number of free corpuscles in a cubic 
centimetre of sodium, the agreement is not so good. In fact, we find from the 
experimental results that for 9 = 628, log^Q C — logio ^ = 2‘G15 ; whence, putting 
in an estimated value of the area of the sodium surface, we get n = 10“® about. The 
value of n has not been determined for sodium by any other method, but we should 
expect it to be not greatly different from that for copper, which is given by 
Mr. Patterson as 3 X lO'f The value given by this method is thus far too great, 
for it is hard to imagine tliat the corpuscles can have a j^i'essure of ten million 
atmospheres. I believe the discrepancy here is greater than can be explained Ijy 
eiTois of experiment, although that was possible in the case of the high values found 
for carbon. 
3 z 2 
