Mr. J.N. Heardcr on a powet'ful Form 



B^^iare this with a similar unit when charged by the electrical 

 3iiiachine; and this I found, with tlie striking distance which I 

 had employed, as nearly the same as so small an indication on 

 the scale as 1 degree would enable me to judge. On increasing 

 or diminishing the striking distance of the balls when using the 

 electrical machine, the fluid indicated the action of the well- 

 -established law, that the effect is in proportion to the square of 

 -4he striking distance, the charged surface being constant. No 

 f%uch law as this was however observable with the induced cur- 

 rent ; for, on the contrary, it was ascertained by subsequent ex- 

 periments that the effect on the wire was diminished when the 

 striking distance was prolonged beyond a certain limit, a fact at 

 -variance with hitherto-recognized laws of electrical action. 

 ,5 As the foregoing experiments wei*e performed with a large 

 ■ jar, which required that the induction coil should be very in- 

 ' tensely excited, thereby rendering its action less permanent, 1 

 subsequently employed smaller jars, and found the same class of 

 results to accompany their action, but with others which the 

 conditions of the first experiments had not enabled me to discover. 

 14. Having satisfied myself that the nature of the charge in 

 the jar was the same with the induction coil as with the machine, 



• I next proceeded to examine the effect of varying the extent of 

 .surface; and as my object was more to compare results with 

 ,'each other, under the action of the induced current, than to 



establish any connexion between these phsenomena and those of 

 "the common electrical machine, I resumed the use of points in 

 ^the discharger, which, from the greater length of spark obtain- 

 "•ible by them, enabled me to vary the striking distance over a 

 greater extent, and thereby more closely to examine the differ- 

 i-*iences of effect.' ^»if'f '^^'^^ oie/j s.Ur'xMnjqx*) lo • 

 i 15. A' jar containing 3 s(|Tiare feet of surface was employed, 

 Yand the thermo-electrometer gave an indication of about 90 de- 

 grees, falling 3 or 4 degrees as the points were withdrawn to the 

 greatest striking distance nearly 0*3 of an inch, but rising again 

 as the distance lessened, until they were brought so near that the 

 negative point became heated, at which time the fluid fell 20 or 

 80 degrees, the diminution of temperature in the electrometer 

 being greater as the negative point became hotter. As soon as 

 the negative terminal became heated, the noise of the sparks was 

 much less, and they assumed a more diffused and flame-like 

 '• eharacter. On withdrawing the points again from each other, 

 the temperature in the electrometer increased as the heat of the 

 negative terminal diminished ; and when the points had been so 

 far withdrawn that the negative terminal ceased to be heated, 



• the sparks suddenly resumed their noisy character, and the fluid 

 -^^^ suddenly rose to about 90 degrees. 



16. A jar of 1 square foot, but of rather thinner glass, pro- 



