ON THE MAGNETIC QUALITIES OF IHON. 
989 
Fig. 2 
is symmetrical with the one sketched. As a matter of convenience in exhibiting the 
results, the portion CD may be sketched as extending from a point C' back to the 
starting point A, as in fig. 3 , OC' being taken equal to OC, and in this way the 
Fig. 3. 
relations of the rising and falling curve to one another are more clearly .shown. There 
is, of course, no need to draw the other half of the cycle. The ordinate of A is taken 
as equal to half the magnetic change which occurs on reversal of the full strength of 
the magnetizing current. 
G^, used in measuring the magnetizing current, was a mirror galvanometer, strongly 
shunted and provided with a strong controlling field. Its constant in the shunted state 
was determined daily by means of the Kelvin centi-ampere balance. The ballistic gal¬ 
vanometer was provided with a usual arrangement for applying electromagnetic impulses 
to stop the swing of the needle. Its readings were reduced to absolute measure by 
means of the coil C, an air induction coil, whose dimensions were accurately measured, 
and the coefficient of mutual induction of its coils calculated from them. Its induction 
was sufficient to give a ballistic deflection of the same order of magnitude as that given 
by the sample under test. The resistance of the ballistic circuit w^as not altered through¬ 
out an experiment, and the two secondaries were permanently connected in series 
