Doolittle tap bell telephone

One of many telephone innovations by Thomas B. Doolittle. Before the invention of the hand-cranked magneto (which generated its own electricity to ring a loud bell), early telephones relied on local wet-cell batteries. To call the operator or the other party, you would press a manual signaling key. This sent a pulse of current that caused a heavy cast-metal bell on the receiving end to give a single "tap." Doolittle's innovation was to stamp the bells from sheet metal instead, which made the telephones significantly lighter, cheaper, and easier to mass-produce. Doolittle's tap telephones were manufactured in Charles Williams Jr's shop.