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"The sounder is a telegraphic receiver consisting of an electromagnet, and a pivoted armature that plays up and down between its stops as the circuit is alternately made and broken. the message is 'read by sound,' i.e., from the clicks made by the armature, substantially as indicated [before]." -Avery 1895

Telegraph Sounder

"The sounder is a telegraphic receiver consisting of an electromagnet, and a pivoted armature that plays…

"A variation of the telegraph sounder that uses a pool of mercury to close the circuit to produce the sound when a click is received." -Avery 1895

Telegraph Sounder

"A variation of the telegraph sounder that uses a pool of mercury to close the circuit to produce the…