Conventional Symbols. The usual diagrammatic symbols for hand and
head receivers are shown in Fig. 59. They are self-explanatory. The
symbol at the left in this figure, showing the general outline of the
receiver, is the one most commonly used where any sort of a receiver
is to be indicated in a circuit diagram, but where it becomes
desirable to indicate in the diagram the actual connections with the
coil or coils of the receiver, the symbol shown at the right is to be
preferred, and obviously it may be modified as to number of windings
and form of core as desired.




CHAPTER VII

PRIMARY CELLS


Galvani, an Italian physician, discovered, in 1786, that a current of
electricity could be produced by chemical action. In 1800, Volta, a
physicist, also an Italian, threw further light on Galvani's discovery
and produced what we know as the _voltaic_, or _galvanic_, cell. In
honor of these two discoverers we have the words volt, galvanic, and
the various words and terms derived therefrom.

Simple Voltaic Cell. A very simple voltaic cell may be made by
placing two plates, one of copper and one of zinc, in a glass vessel
partly filled with dilute sulphuric acid, as shown in Fig. 60. When
the two plates are not connected by a wire or other conductor,