60 Scientific Intelligence. 
core of the joe ton babe raid the surface of the end of the 
cylinder entirely free from filin If filings are scattered upom 
esting to refer to some experiments made by Lt.-Comm. A. 
Caldwe . S. N., and ourselves, on demagnetization. These 
experiments w ere made in 1880 , but have not “been published. 
Perfect demagnetization, or entire absence of magnetism in a 
mass capable of 1etism, is a condition of great spoils 
Approximate euinpneiteitiol has ae brought about with so 
difficulty, but delicate tests would show traces of polarity. 
e have, however, discovered a method by which complete 
demagnetization —— "be rapidly and easily produced. The prin- 
vibration, by which all previous magnetic conditions are obliter- 
ated, and on the subsidence of which no polarity remains. This 
state of vibration is induced by an alternating current of sufficient 
strength. By this an effect is induced in the magnetized mass. 
which can only be compared toa ae or wave. The reversals. 
of the inducing current cause corresponding reversals of polarity 
in the body acted on, and as these rey ties are continuous and 
very rapid (5,000 to 6,000 a minute, for mple), a molecular 
sibencion probably arises. It is prob his “that a condition of 
strain or set is one of the phenomena of magnet 
e particles have been made to assume a sorbate definite or 
it 
become complete,— —that is, involving the whole mass,—all pre- 
vious conditions of strain or “permanent set” will be overcome. 
It must be remarked that, in order to perfectly attain this result 
in all cases, ses exciting force must be sufficient. 
- alternating current ceases, the body acted on is left 
tly free from polarity. It is, however, in a state of extreme 
Fnstivness and must be allowed to remain at rest for a short 
ime. If it is placed north and south, it will assume polarity, and 
Mes ey if struck with a hammer when held in the positiow 
Demagnetization requires but a short time in most cases,—from 
one to three minutes if the current is properly adjusted. There 
die away. Also, when the object is taken out of the coil, i 
” carefully shielded ary the earth’s induction; or the coil may 
e so constructed that it can be opened or divided at the center 
