104 Scientific Proceedings, Royal Dahlia Society. 



wire, -ffj was opeued and Ki closed, and tlie eartli-inductor turned through an 

 angle of 90° in the horizontal component of the Earth's magnetic field. 



The distance of the scale and light spot from tlie mirror of the 

 galvanometer was 101"3 cms. throughout the experiments, and the constant 

 of tlie galvanometer was measured in the usual way by means of the earth- 

 inductor, and found to be practically 70 x 10"'" coulombs per scale- division, 

 and 700 divisions on the scale equalled 44 cms. 



Before coming to the subject proper of this paper, I shall explain how 

 an interesting experiment can be made with this simple arrangement, to show 

 the presence of a transitory electric current due to circular magnetisation 

 produced by twisting an iron wire, wliich is hanging or placed iu a magnetic 

 field. 



A No. 16 ordinary soft iron wire was suspended in the earth's vertical 

 field about 0"45 c. g.s. unit, and when tlie weight on the end of the wire was 

 turned or twisted round the central axis of the wire, a momentary electric 

 current was produced, giving a throw on the ballistic galvanometer. The 

 transitory current thus obtained flowed down the wire when the weight was 

 twisted from left to riglit with respect to an observer standing beside the 

 wire. 



The galvanometer was temporarily taken out of cii'cuit, and it was found 

 \>j calculation and experiment that a length of 227 cms. of the wire, with a 

 vibrator of about 6000 grammes at the lower end of it, had the same period 

 of torsional vibration as the period of vibration of the galvanometer coil, 

 viz., 3'69 sees. 



The galvanometer was now put in circuit, and a series of observations 

 taken thvis :— The vibrator was turned through an angle of, say, 45°, and 

 allowed to vibrate freely round the axis of the wire. The current produced in 

 the wire caused the galvanometer coil and the spot of light to swing in 

 unison with the vibrator ; then the 4th and 5tli swings of the light S23ot were 

 read off in every case, and the mean of tlie two taken. The vibrator was 

 now started from 90°, and so on up to two whole turns. 



The results obtained are shown in Table I. and as a curve in fig. 2. 



