1912-13.] Electrical Resistance and Magnetization of Nickel. 205 
The first group of five measurements is obtained with no transverse 
field, the longitudinal field being put on and removed twice with change of 
direction between the first and second applications. The transverse field is 
then applied and kept steadily in action for the next five successive sets of 
measurements, the longitudinal field being put on and off with reversal of 
direction as before. In the next group the longitudinal field is in its turn 
applied steadily, while the transverse field is put on and off just exactly as 
the longitudinal field was manipulated during the first and second groups of 
measurements. Finally, in the fourth group the longitudinal field is thrown 
off altogether, and the tranverse field applied and removed by itself in a 
cyclic manner, as was done with the longitudinal field in the first group. 
The field which is put on and off twice in succession with reversal of 
direction will be distinguished as the “ cyclic field ” ; and the other, which 
for the time is being maintained, as the “ steady field.” 
The application of the cyclic field is indicated at the left-hand margin, 
the presence or absence of the steady field at the head of each group of 
five measurements. 
It will be noticed that the steady field is applied only in one direction. 
In the early sets of experiments observations were made with the steady 
field, first in one direction, and then in the other. The effect, however, is 
quite independent of the direction of the field. This is clearly shown by 
the fact that the second differences in the fifth column of numbers are 
almost exactly the same for the two directions of the cyclic field. These 
second differences are calculated on the same principles as the first differences. 
Each is the difference between the deviation of exact balance when the 
cyclic field is on and the mean of the preceding and succeeding deviations 
from exact balance when the field is off. 
The closeness in value of the second differences in each group is in fact 
a check on the accuracy of the experiment. This is well brought out in 
the experiment shown. In the majority of cases the same satisfactory 
result was obtained, although in some instances the agreement was not 
quite so good. 
This agreement between the two values of the second differences is the 
more striking when it is noticed that the first differences in each group 
vary greatly among themselves. If no other resistance-changing cause 
were present than the application and removal of the magnetizing forces, 
the first, third, and fifth in each column of first differences should be the 
same ; and similarly the second and fourth should be the same. But in 
each series there is a steady change, which is at once explained as due to 
the heating effect of the current which establishes the longitudinal field. 
