This shows that the two **electricities** neutralize each other's effect when imparted equally to the same conductor.

Accordingly, since every tube sent out from a charged conductor must end somewhere on another charge of opposite sign, it follows that the two **electricities** always exist in equal quantity, and that it is impossible to create any quantity of one kind without creating an equal quantity of the opposite sign.

This theory of the Leyden phial Franklin supported very ingeniously by showing that the outside and the inside coating possessed **electricities** of opposite sign, and that, in charging it, exactly as much **electricity** is added on one side as is subtracted from the other.

Possessed opposite **electricities**, so that in charging the jar as much positive **electricity** is added to one side as negative to the other, led Franklin about 1750 to suggest a modification called the single fluid theory, in which the two states of electrification were regarded as not the results of two entirely different fluids but of the addition or subtraction of one electric fluid from matter, so that positive electrification was to be looked upon as the result of increase or addition of something to ordinary matter and negative as a subtraction.

- Alessandro Volta (1801) showed that although a separation of the two **electricities** was produced by the contact of two different metals (Volta Effect), which could be detected by a sensitive electrometer, a continuous current of corresponding magnitude could not be produced in a purely metallic circuit without the interposition of a liquid, because the electromotive force at one junction was exactly balanced by an equal and opposite force at the other.