R. W. Willson—Demagnetization of Electro-magnets. 347 
of electro-magnets the helix, by which the bar was originally 
magnetized, is still acting with its full power when the demag- 
netizing helix in introduced into the circuit. 
A natural inquiry was this: if the bar were magnetized b 
the weaker helix B, and then demagnetized by the helix A, 
what additional amount of magnetism could A impart to the 
bar? It is evident that this case, though somewhat similar to 
the former, is not identical with it; here the helix B acts as 
resistance to the magnetization of the bar, while in the former 
case it acted to deprive the bar of a portion of the magnetism 
which it already possessed. 
Accordingly the bar, being magnetized by B, was submitted 
to the action of A, and the weigh supported being noted, the 
reverse operation was performed, and the weights supported 
compared as follows: 
A demagnetized by B. B demagnetized by A. 
85 65 
70 65 
65 60 
65 50 
It will be noticed that the results in the left hand are larger 
than those in the right hand column, that is, when A is simply 
demagnetized by B, it can support a greater weight than when 
4 given helix, traversed by a given current, has more power to 
hagnetize than to magnetize, while its power to prevent mag- 
hetization is greater than either. 
