144 
PHYSICS: E. H. HALL 
Proc. N. a. S. 
q and X'o , different ones in succession for each metal, and have then worked 
out the corresponding values of the other quantities, following the order 
Cl, C. 
Values of q and X'o that would lead to values for C greater than 1 or 
less than 0 are of course rejected, as such values of C would be meaning- 
less, but negative values of d and are not to be regarded as impossible. 
I was at first inclined to the opinion that the ratio {kf -^ k) would always 
increase with rise of temperature, but this is not a logical necessity, in 
the present state of our knowledge, and it appears from what follows 
that the ratio in question is quite as likely to decrease as to increase in 
the temperature ascent from 0° to 100°. An interesting relation between 
this conclusion and the observations of Bridgman on change of resistance 
under pressure, at various temperatures, will be shown in this paper. 
Cases in which K2, or B, is 0: In twelve of the seventeen metals for 
which Bridgman gives the value of a the B of equation (16) is zero. Such 
cases are very easy to deal with. We have K2 = 0, and so, from equation 
(15), C2 = 0, unless q has the improbably large value 6.5. If G is 0, 
we have, from equation (14), 
G = Ki (or A) 
R 
(4-g). 
(18) 
Substituting for Ci in equation (17), we get 
C = [- i^,. I 273(1.5 -g)) ^ (4 - ?)] ^ (1.5-?). (19) 
For any given value of q this becomes 
C = i^-'X'o — K" 
(20) 
where and K'^ are new constants, the values of which depend on q. 
This equation shows that, for a fixed value of q, we can represent the 
X 
Fig 
relation of C to X'o by means of a straight line drawn on the (C-X'o) plane. 
Such a line is useful for purposes of interpolation and extrapolation. 
It is to be noted that the metals for which K2 is 0 fall into two groups, 
for one of which Ki is positive, while for the other it is negative. 
Figure 2 shows the general character of the set of g-constant lines for 
the first group, and figure 3 does the same for the second group. 
