Date: October 18, 1887
Creator: Foster, George W.
Description: Patent for a new and improved electric call or signal apparatus. This design consists in "a telegraph or telephone circuit, the combination, with a polarized electro-magnet and a short circuit around the same, which is closed when the magnet is transversed by a constant current of a given polarity, of a battery having the proper pole to line, a switch for connecting the line and battery circuits, and a telephone in the battery circuit, whereby the telegraph or telephone line may be tested" (lines 41-49).
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