12 
by taps tapped at the same time. The medium current 
before used was now passed through the primary coil, and 
as before the kick due to breaking it was observed, and was 
found to be equal to the preceding observation, at least, to a 
close approximation. The ring was again magnetized with 
the maximum current, the process of demagnetization carried 
out as before, and another observation of the temporary 
induction due to the medium current was obtained. This 
was repeated several times, and the observations were found 
to agree, thus showing that, though the ring had been mag- 
netized nearly to saturation, yet it could be brought back 
to its original state by this process of demagnetization. 
Measurements of the Magnetic Induction and Perme- 
ability . — The ring having been demagnetized by the above 
method, a set of observations of the magnetic induction and 
permeability with varying magnetizing force was taken, and 
the results are embodied in Table I., where — 
B is the total magnetic induction ; 
is the temporary magnetic induction ; 
Bj, is the permanent magnetic induction ; 
and fx, jUj, are the corresponding expressions for the mag- 
netic permeability. The manner of taking the observations 
was this : the current being on, in, say, the -h direction, the 
kick on breaking was observed (-}- to 0). It was next 
suddenly passed in the — direction, and the kick due to 
this was observed (0 to — ). The current was now alter- 
nated a few times, and finally passed in the -f- direction. 
It was lastly reversed, and the ensuing kick noted (d- to — ), 
which should be equal to the sum of the other two kicks. 
The first kick is due to the temporary magnetism, and the 
last to double the total magnetism. The ring was now 
again demagnetized, and a fresh set of observations taken, of 
which Table II. is a summary. 
