48 Proceedings of the Royal Society of Edinburgh. 
3 
where q — ^ — ~ 2 , u m 2 being the mean square velocity of the electrons; and 
Zu m 
s is given by the relation 
m 
~o 
= potential energy relative to atom at distance r. 
It will be seen that the signs of Q and P vary according as s is greater 
or less than 4, while the signs of R and S are always the same ; so that, 
taken in conjunction with J. J. Thomson’s suggestion, this statement of the 
theory is capable of accounting for at least the signs of the four effects. 
The four expressions given above are rather complex, but by taking 
ratios we obtain the values : 
2 + 
R 
7s 2 + 8s + 16 e 
8s(s + 1 ) 
These are comparatively simple, and the only unknown is s, which can 
be calculated from the ratios found by experiment. 
The following table gives the values of s for the different metals, 
R 0 
calculated from the observed values of p and g respectively. 
Values of s. 
R 
From 
H 
O 
^j<D 
Iron 
57 
57 
Nickel 
10*0 
9-7 
Cobalt 
2-4 
1-8 
Silver 
3-6 
3-6 
Copper 
3-3 
3*5 
Zinc 
5T 
4-6 
Cadmium 
5*1 
5-2 
Aluminium 
4-8 
4-6 
The two values of s agree reasonably well except in the case of cobalt.* 
The value of s for silver differs widely from the value for nickel, and 
* The cobalt plate was prepared with some difficulty by electrolysis, and was not so 
satisfactory as the plates of the other metals used. On this account the results for cobalt 
cannot be considered as having the same accuracy as those for the other metals. 
