and on certain Principles in Electrical Science. 463 



6. When we attempt to charge an electrical jar, J, fig. 3, 

 it is observable, that as the charge accumulates on the inner 

 surface, a corresponding quantity of electricity is forced off 

 from the, outer, and without this double effect takes place we 

 fail to accumulate a charge. 



{e). To render this evident, we have only to place the jar 

 on an insulator, as in fig. 3 ; we shall then find, that for every 

 spark we send into the jar, a similar spark will leave its out- 

 side, either from the coating directly, or from any distant 

 body c connected with it as in fig. 4. 



The outer coating J, therefore, and distant body c, may be 

 considered in their insulated state as being insulated con- 

 ductors under the conditions represented in fig. 2. 



{/). Suppose the jar charged, and that it remains insu- 

 lated ; then we may discharge it, either by one dense shock 

 through the rod /, fig. 4, or gradually, in the reverse way of 

 charging ; viz. by continuing to draw sparks from the knob 

 7)1, and add them to the coating J : the circumstance how- 

 ever of our being enabled to take a finite spark, from either 

 side alternately, whilst the jar rests on an insulator, is suffi- 

 cient to show, that the accumulated electricity is never ex- 

 actly balanced between the opposed coatings, so that there 

 will always be an excess of either positive or negative electri- 

 city over the neutralizing quantities themselves, disposed on 

 the coatings of the jar. 



{S )' ^hen therefore we discharge the jar, this excess of 

 free electricity will speedily expand itself over the outer sur- 

 fiice J, the discharging rod t, the knob of the jar m, or any 

 other body, c, fig. 4, connected with it, which, as in the case 

 of the simply electrified conductor, J, fig. 2, will cause aspiirk 

 to occur in either of those places. The intensity of this spark 

 however will depend on the capacity of the jar. It is less with 

 a large jar, and greater with a small one, the quantity of elec- 

 tricity discharged being the same. 



(Ji). When the jar has been discharged, the knob, the 

 outer coating, and all the bodies connected with it, will be 

 found in the same electrical state. We may make this state 

 either positive or negative, by taking a spark either from 

 the knob or coating previously to discharging the jar. 



{i). This small spark caused by the excess of free electri- 

 city, may be obtained even though the jar be connected with 

 the earth, provided we seize it before the conductors have 

 had time to operate in carrying off' the residuary accumula- 

 tion ; Professor Wheatstone having shown by his unrivalled 

 experiments on electrical conduction, that some portion of 

 time elapses in the passage of electricity through wires. 



