Electrical Discharge. 353 



jars so very different in its action from the others, that I was led 

 to strip off the coating in order to examine the precise condition 

 of the surface beneath. Having done this, I found a thin sheet 

 of paper pasted upon the surface of the glass, which being an 

 imperfect conductor became a source of obstruction in the circuit. 

 When this paper was displaced, and the coating applied imme- 

 diately to the glass, the jar acted in every respect like the others. 

 Every kind of cement, therefore, employed to attach the coating 

 to the glass would cause some resistance to the free translation 

 of the charge, according as it is more or less insulatuig, or of 

 greater or less thickness ; when consisting of any resinous sub- 

 stance, such as common bees-wax, the increased resistance is very 

 considerable. 



20. If we coat a jar with an imperfect conductor, such as 

 water, as in the original experiments of the Germans and Dutch, 

 the resistance to discharge is especially marked. In this case 

 the heating effect of a given quantity of electricity accumulated 

 and discharged from such a jar is almost inappreciable by the 

 thermo-electrometer as commonly employed ; so that if the ori- 

 ginal experiment had been perpetuated under the form first given 

 by the Leyden experimentalists, we should have known very little 

 of the heating effects of the ordinary electrical battery on me- 

 tallic wires. I recently gave a jar 30 inches high and 10 inches 

 in diameter, a coating of 5 square feet of water, the un coated in- 

 terval being carefully varnished, and charged it with a measured 

 quantity of electricity. The indicated "intensity" or "density," 

 according to M. Riess, of the charge, as measured by a statical 

 electrometer, was nearly the same as that of a similar jar coated 

 with metal and charged with the same quantity of electricity. 

 Still the heating effect of the discharge from the water-coating 

 was scarcely appreciable by the thermo-electrometer then em- 

 ployed ; it was certainly not the one-thirtieth part of the effect 

 of the discharge of the same quantity of electricity from the me- 

 tallic coating, although on introducing a tube of water into the 

 circuit, the discharge readily set fire to inflammable matter such 

 as gunpowder. 



21. We find therefore always some resistance to discharge, 

 arising out of the necessary construction of the jar itself, a 

 resistance altogether independent of the resistance proper to the 

 extent of the circuit of discharge, and which it is requisite to 

 consider, and add as a constant whenever we desire to calculate 

 the total resistance. If, for example, we would seek to discover 

 the comparative resistance of metallic circuits varying in length, 

 we must add to the resistance of each circuit this constant 

 resistance in the battery itself, more especially if the quantity of 

 electricity be small and the given circuits of small extent. It is 



