CHAPTER VI.
How to Select Batteries for Gas Lighting.
Before entering into a description of the various batteries used in electric gas lighting, it will be well to briefly consider a few simple electrical rules bearing upon the subject.
A current of electricity has electromotive force, or difference of potential figured in volts, and current figured in amperes.
For example we will use the water analogy (Fig. 49). Two tanks, A B, on the same level, are connected by a pipe C.
Supposing tank A be filled with water and the pipe, C, to be opened; the water will flow along C into B until the level in each tank is equal. So long as there is a difference of level, there will be a pressure in C, owing to the water behind it.
Replacing the tanks A and B by unequally electrified bodies, and the pipe C by a conductor of electricity, the flow of water is represented by the tendency of the electrified bodies to equalize themselves by a flow of current along the conductor, C.
To sum up: The difference of level is now difference of potential, the pounds pressure along the pipe being expressed as electromotive force in volts.
Fig. 49.