58 Ch<t tit — Var ia t ion of Potential along a 



est, i. e., at a current loop ; the effect is least at a current node. 

 With a single wing these results are exactly reversed, — the 

 effect is greatest at a current node, which is, of course, a poten- 

 tial loop. This can be explained in the following way : The 

 little wing and the portion of the wire just beside it act as a 

 miniature condenser, and when there is a maximum variation 

 of potential in the element of wire there will also be a maxi- 

 mum variation in the detector wing, which will cause currents 

 to surge back and forth in the helix and so to demagnetize the 

 iron core. At a current loop (or potential node), the variation 

 in potential is a minimum, and so the detector when placed 

 there will show minimum demagnetization. Indeed the indi- 

 cations of the magnetic detector should be precisely similar to 

 those of the bolometer as used by Rubens. 



An attempt was then made to force standing waves in a 

 wire, and preliminary experiments seemed to show the possi- 

 bility of determining the wave-lengths of oscillators in this 

 way. . Some measurements were made then, which, since 



returning to Toronto, have 



been 



considerably extended. 





j 



l 





A /—\/— v 





t t ft 



« — ^ — > (X> 



) - 



=hd — -o 









a b 





c 





d 





The oscillators were of four kinds, illustrated in fig. 1. The 

 cylinders of (a) were 2*5 cms in diameter and 12*5 cms long, with 

 hemispherical ends ; the spheres of (h) were of two sizes, 

 namely, with diameters of I0 cms and 30 cras , respectively; the 

 larger spherical ends of (c) were 19 mm , the smaller 6 mra , and the 

 straight portion 4"2 mm , in diameter, while the length over all 

 was ]2'5 cms ; in (d) is shown the ordinary Hertzian plate oscil- 

 lator. 



The sparks were produced by an induction coil capable of giv- 

 ing sparks 12'5 cm long, and fed by five accumulators in series. 



The interrupter was similar to that used in the other investi- 

 gation. It consisted in a platinum-tipped rod, which, by 

 means of a motor, was alternately plunged into and with- 

 drawn from mercury, the surface of which was kept clean by a 

 stream of water continually flowing over it. In series with 

 this were a pendulum interrupter and a contact key. This key 

 was depressed during any desired number of vibrations of the 

 pendulum, — usually five swings, — during which time the coil 

 was interrupted approximately sixty times. This number, of 

 course, varied somewhat with the speed of the motor, but it 

 did not change much during any series of readings. 



