Faraday to Henry Minchin Noad   c.1854–1855¹

The same difference will in every case exist between the balls nn’, Fig 96, when a spark is ready to pass. Thus, suppose the unit jar has about one tenth of the electric capacity of the large jar J, Fig. 97, and that being charged up to its discharging point, it contains ten of positive Electricity; then these ten will pass on into the large jar as a discharge spark, and none will remain within the unit jar. Now, the conductor of the machine, the outside of the unit jar, and the ball and wire of the large jar, will all appear positive to a carrier ball. But when the machine is turned, although a rise in positive condition will gradually take place on all the surfaces, still the mutual relation of n and n’ to each other will be the same as before, and the mutual relation of the inner and outer coating of the unit jar will be to each other absolutely as before; for no external relation can alter their mutual relation, though it may affect the outer coatings, both of the large jar and of the unit jar. So the machine must exert a higher charging power than before, which is shown by placing an Electrometer on its conductor; and when then units have been thrown into J, then, if after the eleventh the machine conductor be discharged, the jar J will be discharged back between n and n’, because of the re-action backwards. Still, whenever a spark does pass from n to n’, the Electricity passing must be equal; because the inductive relations of the coatings to each other through the glass, and the like relations of the balls n n’ to each other, remain absolutely the same. This is, as I think, a rigid consequence of the principles of inductive action.