I" ELECTRICITY IN MOTION. 



The condenser acts in some measure on the same principle - 

 the electrophoru;, both instruments u< living tln-ir properties from 

 the . induction. The use of tlie condenser is to collect a 



k electricity from a lar^e substance into a smaller one, so at 

 to inak.-' its density or tension sufficient to he examined. A small 

 plate) connected with the substance, is brought nearly into con- 

 tact with another plate communicating with the earth ; in gi 

 a thin stratum of air only is interposed; but sometimes a noncon- 

 ducting varnish is employed ; this method i*, however, liable to 

 some uncertainty, from the permanent electricity which the var- 

 nish sometimes contracts by friction. The electricity is accumu. 

 lated by the attraction of the plate communicating with the earth, 

 into the plate of the condenser : and when this plate is first M pi- 

 rated from the substance to be examined, and then removed from 

 the opposite plate, its electricity is always of the same kind with 

 that which originally existed in the substance, but its tension is so 

 much increased as to render it more easily discoverable. This 

 principle has been variously applied* by different electricians, and 

 the employment of the instrument has been facilitated by several 

 r-uhordinatc arrangements. 



Mr. Cavallo's multiplier is a combination of two condensers; 

 the second or auxiliary plate of the first, like the plate of the 

 electrophorus, is rnoveable, and carries a charge of electricity, 

 contrary to that of the substance to lie examined, to the first or 

 insulated plate of the second condenser, which receives it repeat, 

 cdly, until it has acquired an equal degree of tension 3 and when 

 the two plates of this condenser are separated, they both exhibit 

 an electricity much more powerful than that of the condenser. 

 The force is, however, still more rapidly augmented by the instru- 

 s of Mr. Bennett and Mr. Nicholson ; although it has been 

 supposed that these in-truments are more liable to inconvenience 

 from the attachment of a greater portion of electricity to the first 

 plate of the instrument, which leaves, ior a very considerable time, 

 lain quantity of the charge, not easily separable from it. Mr. 

 Hennet employs throe varnished plates laid on each other, but 

 Mr. Nicholson has substituted simple metallic plate-, approaching 

 near together, so that there can be no error from any 

 accidental friction. In both of these instruments, the second plate 

 of a ; acquires an electricity contrary and very nearly 



equal to that of the first, by means of which it brings a third platv 



