a rapid succession of Electrical Discharges. 331 



an almost corresponding increase of these effects, the mind is 

 naturally led to inquire whence this additional power is derived, 

 and whether any of the correlative physical forces operating to 

 produce it have undergone any material change in their cha- 

 racter. Here is an abundant field for inquiry, and the practical 

 determination of the nature of these mutations may serve to in- 

 dicate the extent to which the electrical developments resulting 

 from a given amount of inducing magnetic action may be carried. 

 So far as I have gone, they appear to be pretty nearly coincident 

 with the lengths of secondary wire employed, though certain 

 considerations would lead to the inference that the external 

 layers of the secondary wire would be less effective than the in- 

 ternal ones. One effect is worthy of remark in passing : it is 

 the apparent absorption of the magnetic intensity of the coi'c 

 under certain conditions of the induced current, as is evidenced 

 by the action of the vibrating spring, Avhose energy is much in- 

 fluenced by alterations in the character of the secondary circuit, 

 and whose vibrations become occasionally much enfeebled when 

 the circuit is quite closed. 



The thermal effect, then, of the current upon an external cir- 

 cuit will depend upon the quantity of electricity transmitted in 

 each wave, and the electrical capacity of the terminal or trans- 

 mitting conductors, up to the point at which they are fully 

 capable of containing all the electricity sent forward to them. If 

 of too small dimensions, the thermal effect produced will be only 

 equivalent to the quantity of electricity which they can contain at 

 the instant of the discharge ; and thus if the transmitted wave con- 

 tain more than they are adequate to appropriate, it is evident that 

 the effect of the whole quantity cannot be transmitted at once, 

 but must partake in some measure of the character of the stream- 

 like discharge from the terminal screws alone, one portion only 

 acting as a Leyden dischai'ge, and the remainder passing like a 

 stream which overflows a vessel already full. 



As the determination of the quantity of electricity developed 

 by the coil, and its comparison with some of the effects produced 

 by statical or frictional electricity derived from other sources, 

 appeared to be practicable and likely to afford some interesting 

 results, I instituted a series of experiments with a view to ascer- 

 tain this relation, and the results quite confirm the estimate 

 which I had previously formed of the extraordinary power of the 

 coil. The thermo-electrometer described (Phil. Mag. vol. xii. 

 p. 379. par. 4) appeared to afford a ready and efficient standard 

 of comparison for this purpose, since it was affected both by the 

 electricity of the coil and that of the electrical machine, and its 

 indications j)roved the identity of the two agencies. 



Witliout stopping to discuss the merits of the instrument as a 



