METEORIC AND ARTIFICIAL NICKEL-IRON ALLOYS. 
31 
secondary containing no iron. On now making or breaking the current in the 
inductor primary the galvanometer throw was 6'43 centims. 
The artificial nickel-iron ring showed a similar behaviour, but the differences between 
the various throws were much smaller than in the case of the meteoric iron, just as 
the observed hysteresis effect was much less. 
The interpretation of these results is, of course, simple. The throw was greatest 
when the ring secondary was replaced by an equal resistance containing no iron 
because of the absence of hysteresis. This throw is that required for the correct 
calculation, in the usual way, of the value of the induction in the iron from which the 
permeability is deduced. The throw obtained on first completing the inductor 
primary circuit, after demagnetisation of the iron ring, was greater than the 
subsequent throws, which were practically equal, for a reason which is immediately 
obvious on consideration of the form of the curve showing the change of induction in 
an iron ring when subjected to a cyclic field. 
Assuming the ring to be demagnetised, the effect of the transient current in its 
secondary when the inductor primary circuit is established is to change the induction 
in the iron in the way represented by the curves 
Obi, bib 2 . The final induction in the ring secondary is 
indicated by O b 2 and the magnitude of this ordinate 
is a measure of the difference between the first 
throw after demagnetisation and that obtained from 
a similar circuit containing no iron. When the 
current in the inductor primary is broken, the 
induction in the ring secondary changes in a way 
represented by b 2 b 3 b 4 , and the line b 2 b 4 represents the 
total change of induction in the ring secondary 
during the second step. Similarly bj) 2 represents, 
approximately, the total change of induction when 
the inductor primary circuit is again completed, and 
so on. The length of b 2 b 4 being approximately double that of 0 b 2 , the effect of 
hysteresis is more pronounced in the second and succeeding throws than in that first 
observed after demagnetisation. 
Assuming this to be the correct interpretation of the results, there follows at once 
a method of eliminating the effect of hysteresis directly without substituting for the 
ring secondary an equivalent resistance not containing iron. Suppose that, after 
demagnetising, the inductor primary circuit is completed. This causes a galvano¬ 
meter throw which need not be recorded and leaves the induction in the ring- 
secondary in the state represented by O b 2 . Now open the secondary circuit and then 
open the inductor primary circuit.' Now close the secondary circuit again. The 
induction in the ring secondary will still be represented by 0 b 2 . Finally complete 
the inductor primary circuit again and observe the galvanometer throw. This throw 
Fig. 6. 
