1913-14.] Resistance of Iron in Crossed Magnetic Fields. 261 
reading produced when the current was in the one direction being sub- 
tracted from the mean of the readings immediately preceding and succeed- 
ing with the current in the other direction. Five successive sets of such 
triplets of readings were taken as quickly as possible : (1) with no magnetiz- 
ing force applied, (2) with the magnetizing force applied in, say, the positive 
direction, (3) with no magnetizing force applied, (4) with the magnetizing 
force applied in the negative direction, (5) with no magnetizing force 
applied. Each triplet gave a first difference of deflections ; and from the 
five first differences two second differences were obtained by subtracting the 
second from the average of the first and third, and the fourth from the 
average of the third and fifth. The average of these two second differences 
was the final value of the deflection due to the application of the magnetis- 
ing force. By means of the standardizing experiment this final value was 
reduced to absolute measure in the form c^N/N, where N is the resistance 
of the iron or steel strip. 
The calibration experiment involved the observation of at least nine 
distinct readings ; and the final value of the deflection in the experiment 
just described involved fifteen distinct readings. Hence the value of any 
one of the ratios, c?N/N, is deduced from twenty-four distinct galvanometer 
readings. 
A complete set of observations for any given pair of fields, the one 
longitudinal and the other transverse, required four groups of the fifteen 
readings just described. The first group was obtained with no transverse 
field, the longitudinal field being put on and removed twice with change of 
direction between the first and second applications. In the second group 
the transverse field was applied and kept steadily in action, the longitudinal 
field being put on and off with reversal of direction as before. In the third 
group the longitudinal field was kept steadily applied in its turn, and the 
transverse field was put on and off exactly as the longitudinal field was 
manipulated during the first and second groups. Finally, in the fourth 
group the longitudinal field was thrown off altogether and the transverse 
field applied and removed by itself in a cyclic manner, as was done with 
the longitudinal field in the first group. 
The field which was put on and off with reversal of direction is dis- 
tinguished as the “ cyclic field ” ; and the other, which for the time is being 
maintained, is called the “ steady field.” 
For other details of the method, and for the investigation of the complete 
theory, reference may be made to the earlier paper. 
In the Appendix, which contains all the measured values of the changes 
of resistance, and in what follows here, the horizontal field will be re- 
