w^^'^ \ of the Induction Coil.. , , ,. 



in the velocity of the current under the two different con- 

 ditions. 



11 . In the foregoing experiments, the discharging electrometer 

 was fitted with platina points, between which discharges can be 

 obtained of a greater length than between balls ; but in order to 

 place the experiment under conditions which would admit of 

 better comparison with the effects of the ordinary electrical 

 machine, I substituted balls for points in the discharger. On 

 placing them at such a distance from each other as to allow the 

 discharges to pass, the fluid instantly rose to a definite height in 

 the tube, nearly 100 degrees ; and whilst thus permanent, the 

 balls of the discharger were gradually approximated to each other, 

 with no diminution of effect, until they were in absolute contact, 

 when, the circuit being closed and the jar no longer capable of 

 receiving a charge, the fluid instantly fell nearly to zero, the 

 residual amount of expansion being due to the heat absorbed by 

 the glass surface, &c. during the continuation of the experiment. 

 On the slightest separation of the balls from each other the fluid 

 rose to 100 degrees, and remained tolerably permanent until 

 they were separated beyond the striking interval, when the fluid 

 again fell as soon as the discharges ceased. ^^ 



12. The balls were next placed rather within the greatest 

 striking distance ; and instead of allowing the spring to vibrate 

 and produce the ordinary rapid succession of discharges, 1 held 

 it in my hand and broke contact at successive single slow inter- 

 vals, in order to ascertain the value of a single discharge; this 

 I found to be only 1 degree on the scale of the instrument. On 

 making an interruption of the circuit, the action of the fluid was 

 precisely of the same character as if the jar had been charged by 

 the electrical machine, that is to say, the fluid rose with a sudden 

 impulse and instantly subsided. On repeating the intetruptions 

 at rather quicker intervals, so as to make each successive inter- 

 ruption before the effect of the preceding one had quite subsided, 

 the fluid was made to rise 1 degree in succession for each dis- 

 charge, so that 1, 2, 3, and so on to 12 discharges, just raised 

 the fluid correspondingly to 1, 2, 3, to 12 degrees. There was 

 some little difficulty in manipulating in this way, as the discharge 

 did not always take place at each interruption in the circuit, 

 owing to variations in the character of the metallic contact at 

 the interruptor, arising from the oxidation of the platina surfaces; 

 but as far as they went they were sufficient to show that the extra- 

 ordinary result first noticed was due to a rapid succession of 

 units of effect gradually accumulating in the transmitting wire. 



13. Having thus established a means of comparing the effects 

 of the coil with those of the ordinary electrical machine, and 

 having ascertained the value of a unit of discharge under the 

 influence of the induction coil, it rext became necessary to com- 



