PHILOSOPHICAL TRANSACTIONS. 
I. A Magnetic Detector of Electrical Waves and some of its Applications. 
By E. PtUTHERFOP.D, M.A., 1851 JExhihition Science Scholar, New Zealand Univer¬ 
sity, Trinity College, Cambridge. 
Communicated by Professor J. J. Thomson, F.R.S. 
Received June 11,—Read June 18, 1896. 
Introduction. 
The present paper deals with the subject of the magnetization of iron by high- 
frequency discharges, and the uses of magnetized steel needles for detecting and 
measuring currents of very great rapidity of alternation. 
It will be shown that these magnetic detectors offer a very simple means of 
investigating many of the phenomena connected with high-frequency discharges, and 
may be used over a wide range of periods of alternation. Not only may these 
detectors be used in ordinary Leyden jar circuits, but they also offer a sensitive 
means of investigating waves along wires amd free vibrating circuits of short wave¬ 
lengths. 
They were also found to be a sensitive means of detecting electrical radiation from 
Hertzian vibrators at long distances from the vibrator. 
In the course of the paper the following subjects are investigated :— 
I. Magnetization of iron by high-frequency discharges and the investigation of the 
effect on short steel needles. 
II. Alagnetic detectors and their uses. 
a. Detection of electro-magnetic radiation in free space. 
AVaves were detected over half-a-mile from the vibrator. 
b. Waves along wires. 
c. Damping of oscillations. 
Resistance of iron wires. 
Absorption of energy by conductors. 
d. Determination of the period of Leyden jar discharges and the constants of 
the discharcje circuit. 
The magnetization of steel needles when placed in a spiral through which a Leyden 
jar discharge was passed has long been known. 
MDCCCXCVII.— A. B 22.2.97 
