234 Intelligence and Miscellaneous Articles, 



The experiments I have hitherto carried out refer to the propagation 

 through air only. The very note- worthy influence of electric insu- 

 lators shown in the Italian physicist's experiments required still 

 further study. That also in insulators electrical movements of very 

 brief duration occur which in some circumstances may well operate 

 inductively on their vicinity, similarly to the excitement of magnetism 

 in iron, appears very probable from the influence which such media 

 have as dielectrics. For the time I did not prosecute this part of the 

 inquiry. The interruption-apparatus used by me for the conduction 

 of the currents consisted of a heavy and solid iron pendulum, the 

 support of which was let into the wall, and which was always let fall 

 from the same height. At the lower end it had two projections 

 overlaid with plates of agate, which at the moment when the pen- 

 dulum passed through the position of equilibrium struck the steel 

 ends of two light little levers, by the motion of which two current- 

 conductions were interrupted. One of these levers rested on a fixed 

 support, the other on a slide which could be shifted by means of a 

 micrometer- screw, so that the stroke on this moveable lever resulted, 

 by any small period chosen, now sooner, now later than that on the 

 other. The interval of time was calculated from the micrometrically 

 measured displacement of the striking-point and from the velocity of 

 the fall of the pendulum ; the latter was calculated from the time and 

 arc of oscillation of the pendulum. A division-mark on the head of 

 the micrometer-screw corresponded to ^TiTTO" °f a second. With 

 present arrangements it would have been useless to take more accu- 

 rate readings, on account of the inequality of duration of the spark. 

 As it was important to have the distances between the spirals as 

 great as possible, I gave to them the form of rings of about 80 ceii- 

 tims. diameter. The inducing spiral had only 12j turns of copper 

 wire 1 millim. thick, covered with J millim. thickness of gutta 

 percha. The induced spiral, on the contrary, had 5 GO turns of cop- 

 per wire, spun round with silk, of -J millim. diameter. This spiral 

 could be placed at a distance of 170 centims. from the inducing one 

 without the inducing effect ceasing to be evident. But even the 

 nearest distance to which the two coils were brought amounted still 

 to 34 centims., in order to make the reaction of the induced on the in- 

 ducing current imperceptibly small — which, so far as could be judged 

 by time-measuring experiments, was accomplished. 



In the experiments the following was the arrangement adopted : — 

 The circuit of the inducing current contained a Daniell's element, 

 the smaller spiral, and the first- struck place of interruption. By the 

 stroke the current was stopped ; and i£s interruption operated indu- 

 cingly on the alone remaining second circuit. This was not perfectly 

 closed, but its ends led to a condenser (after Kohlrausch) with two 

 gilt metal disks, which were brought to § millim. distance from one 

 another. This circuit consisted of the larger wire spiral, one end of 

 which was connected immediately with the fixed plate of the con-* 

 denser, in communication with the earth. The other end commu- 

 nicated, through the second interruption-lever, with the insulated 

 moveable plate of the condenser. The electricity put in motion by 

 induction thus flowed into the condenser up to the moment when 



