Electrical Waves and some of its Applications. 185 



The partial demagnetisation of fine steel wires, over which is 

 wound a small solenoid, was found to be a very sensitive means of 

 detecting electrical waves at long distances from the vibrator. 

 Quite a marked effect was found at a distance of over half a mile from 

 the vibrator. 



Detectors made of very fine steel wire may be used to investigate 

 waves along wires and free vibrating circuits of short wave-length. 

 Fine wire detectors are of the same order of sensitiveness as the 

 bolometer for showing electrical oscillations in a conductor. 



This detector also has the property of distinguishing between the 

 first and second half oscillations of a discharge, and may be used for 

 determining the damping of electrical vibrations and the resistances 

 of the discharge circuit. 



A method of experimentally determining the period of oscillation 

 of a Leyden jar circuit by the division of rapidly alternating currents 

 in a multiple circuit is explained. The capacity and the self-induct- 

 ance of the circuit for high frequency discharges may also be deduced, 

 so that all the constants of a discharge circuit may be experimentally 

 determined. In the course of the paper the following subjects were 

 investigated. 



(1) Magnetisation of Iron by High Frequency Discharges. The effect 

 of the Leyden jar discharge on soft iron and steel is fully examined. 

 Steel needles which had been placed in a solenoid and subjected to a 

 discharge were examined by dissolving them in acid. It was found 

 that there was apparently only evidence of two half oscillations in 

 the discharge, and this effect is due to the demagnetising force 

 exerted by the needle on itself during the discharge. 



The effect of continued discharges on the demagnetisation of mag- 

 netised steel needles was investigated, and also the effect of varying 

 the length and diameter of the steel needles. 



When a discharge is sent longitudinally through a magnetised steel 

 wire the magnetic moment of the needle is always decreased, due to 

 the circular magnetisation of the wire by the current through it. 

 This " longitudinal " detector, when of thin steel wire, was found to 

 be a sensitive means of detecting electrical oscillations of small 

 amplitude. 



Both the "longitudinal" and " solenoid al " detectors may be 

 readily used for comparing the intensities of currents in multiple 

 circuits when traversed by currents of the same period. 



(2) Detection of Electrical Waves at Long Distances from the Vibrator. 

 A compound detector needle was composed of fine steel wires and 

 a small solenoid wound over it. When this detector was placed in 

 series with the wires of a receiver, the electrical oscillations set up in 

 the circuit tended to demagnetise the magnetised detector needle. 



By this method electrical waves from a Hertzian vibrator were 



