ELECTRICAL WAVES AND SOME OP ITS APPLICATIONS. 
7 
A thin steel wire, ‘025 centim. in diameter, was completely demagnetized by a 
discharge. In this particular case the maximum value of the current through the 
wire was about 100 amperes, and the value of the magnetic force at the surface of 
the wire was, therefore, about 1600 C.G.S. units. A hard steel wire, '08 centim. in 
diameter, was only partially demagnetized, the deflection being reduced from 250 to 
116 scale divisions. 
The following are examples of a few of the experiments on the demagnetization of 
iron wires when the frequency of the discharge was about 3 million and the value of 
the maximum current about 100 amperes ;— 
1. Thin soft iron 0 . . 
Thin steel rwire diameter, ‘025 centim. : completely demagnetized, 
2. Steel wire : diameter, '08 centim. : fall of deflection from 250 to 116. 
3. Steel wire: ,, T6 centim, ; ,, „ 250 to 184. 
4. Steel wire: ,, ’25 centim. : „ ,, 250 to 216. 
5. Long hollow soft iron cylinder, ^ millim. thick and diameter 1'8 millims. 
of deflection from 250 to 230. 
fall 
The same condenser and discharging current were used for all the specimens 
tested, and it is of interest to observe the depth to which the magnetism of the iron 
was affected by the discharge, assuming that the final deflection is that due to the 
mass of iron not circularly magnetized. 
Wire. 
Diameter. 
Depth of penetration 
of the discliarge. 
centim. 
centim. 
Hard steel wire 
•08 
•013 
Soft steel wire .... 
•16 
•Oil 
Soft steel. 
•25 
•009 
Soft iron cylinder. 
1-8 
•0011 
Experiments of this kind show to what a small depth the current penetrates into 
the iron wire. Very large momentary currents are conveyed through a surface skin 
of the conductor, and the intensity of the current diminishes rapidly inwards. 
A thin magnetized steel wire was placed in the circuit of a small Hertzian plate 
vibrator. The deflection due to the needle fell from 300 to 250 after a succession of 
discharges. 
This shows that the iron was unaffected below a depth of about '0011 centim. 
For rough comparisons of the intensity of currents in multiple circuits, the use of 
the “ longitudinal ” detector is often preferable to placing the needle in a solenoid. 
A thin magnetized steel wire, placed in series with the circuit, is a surprisingly 
sensitive detector of oscillatory currents of small intensity. 
