When a customer enters a telephone booth and closes the door, a switch located in the ceiling and connected to the door by a rod turns on the light. In some booths it starts a ventilating fan. Switches heretofore used for this purpose were mechanical ones which had moving parts to wear out and which made what Bell Telephone Laboratories considered a disagreeable noise.
Described in Bell Laboratories Record last week was a booth switch in the form of a small glass tube containing a pellet of mercury, which is a good conductor of...
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