The new physics - Softcover

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1884 Excerpt: ...from them with reference to this level. In the case of the cell we do not know why there should be this difference of potential between two different metals. It is not necessary at present to enter into theories in regard to the cause of the difference of potential which produces what is called electro-motive force. All we wish to know at present is, how we can connect the phenomena of energy, and measure them all by the same units of time, space, and mass. We can, however, think of a battery as an engine which is pumping up water through one pipe and delivering it through another. Suppose that the engine is in closed at A (Fig. 83), and that the water is lifted through one pipe/ and discharged through another, p'. Suppose that we can not study the mechanism of the engine at A. All we can see and measure is the difference and direction of the pressure in the two pipes p and /'. This difference of pressure is analogous to the difference of potential between the poles of an electrical battery or cell, which maintains in some unknown way an electro-motive force along the wire. We do not know whether there is any current in a wire like that produced by the flow of water in a pipe. We only know that there is a difference of level, and that there are conditions for the performance of work in an electrical circuit. If we could measure this work by the same units with which we measure mechanical work, or the work that is done, for instance, by a weight falling a certain distance under the effect of gravitation, we could compare electrical work or electrical engines with mechanical work, or the work done by machines. Before doing this, let us look more carefully at the way we measure work. We have seen that we can measure the work done by a body falling vertically u...