Reis' telephone
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Reis' telephone, an invention by Philipp Reis by an inspiration from a French article in 1854 (by Bourseul) how to create a microphone-like devices. His first successful work was achieved in October 1861.
Microphone (I) Reis created this using a tensed circular swine-intestine membrane, with a small platinum brick mounted in its centre. Another platinum rod with a nail-like pin in one of its end, rested against the center-brick. Vibrations in the membrane caused the pin to temporary open and close the circuit, thus converting vibrations in the air into electrical signal. This is called a "Make-Break" transmitter, and is capable only of low-fidelity transmission of sound. With careful adjustment, this transmitter is capable of operating in a "loose contact variable pressure" or microphone mode, but Reis was unaware of that prior to his death, and always described the transmitter as "make break". If the platinum contacts are replaced with carbon, this microphone is no different than any other loose contact variable pressure microphone.
Loudspeaker (II) Reis speaker worked by magnetostriction. In his first receiver he wound a coil of wire around an iron knitting needle and rested the needle against the "F" hole of a violin. As current passed through the needle, the iron shrank and a click was formed. The image shown below is a more advanced version where the iron bar is clamped to a cigar box shaped resonator. This receiver is very insensitive; it produces weak sound but has good fidelity. It requires very high current and is a current sensitive device rather than a voltage sensitive device.
Reis was marginally successful. This instrument could transmit continuous musical tones but produced indistinct speech.
Source: Friedrich Georg Wieck, Otto Wilhelm Ålund "Uppfinningarnas bok" vol. II, 1874.