i'm no longer inquiring about the simple tin can telephone but one commercial used in the 1900s that uses springs... the description I found says:
"However, later in the 19th century, “mechanical phone” systems — essentially elaborate versions of “two cans and a string” were actually used in areas not served by Bell’s phone system (and which evaded any of Bell’s patents). Some were complete exchanges with operator switchboards, such as Lemuel Mellett’s “Pulsion Telephone” invented in 1888 for use on American railways.
A newspaper article from 1889 reads as follows: “The Pulsion Telephone was a mechanical telephone which really seems as if it might rival the ordinary telephone, at any rate for moderate distances, has been recently exhibited on a 3 miles line, between Finchley-road and Hendon, on the Midland Railway [Editor’s Note: near London], under the name of the ‘Pulsion Telephone.’ It is the invention of Mr. Lemuel Mellett, of Boston, U.S. [Editor’s Note: Actually he was from Newton and then Somerville, Massachusetts.] The principle seems to be to have on the resounding-plate a number of small coiled springs held at one end only; these respond to various harmonic vibrations, and the vibration of the wire is taken up and reinforced, giving great distinctness of utterance. It seems not to matter much whether the wire is twisted or passes through loose earth. One peculiarity is that it can be tapped at any point by resting a hat upon the wire, a useful quality in case of accident, though evidently unfitting it for private messages.”
I can't find illustration of it. Anyone got any picture of "the resounding-plate a number of small coiled springs held at one end only"... this is just for historical curiosity.
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