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Dead medium: Pneumatic Telegraphy
Source(s): 'Manfacturer and Builder', Volume 3, Issue 6, June, 1871.
From: Tim Howgego
Date: Sun, 3 Dec 2000 20:49:19 -0000

(((Comments from Tim Howgego in the text are /in shashes/ -- tomj)))

"The pneumatic signal apparatus ... is founded on the property of a column of air enclosed in a tube to transmit rapidly any impluse of pressure produced at one end to the other, whether the column be short or many hundred feet in length. Air being a perfectly elastic body, it is evident that any compression produced at one end of the tube will transmit itself by compressing the successive portions, and will travel forward like a wave - in fact, identical to a wave of sound, and with the same velocity as sound, that is, about 1100 feet per second."

The apparatus was based on experiments and observations made by Regnault, in Paris, 1863.

"Fig. 1 in our cut [a large cube shaped box with a display of some kind on the front] shows the annunciator to which the apparatus is applied when used in hotels and large buildings. Besides the arrangement above described for sounding the bell, another causes the number or name of the room to be shown. In all other respects, this annunciator is the same as that in ordinary use. Fig. 2 [a cylindrical pedestal, with an array of buttons on the top surface /last seen in the Tardis (Doctor Who)/] is a woodern pedestal. At B [the top of the pedestal] are a series of buttons, each communicating to one of the bulbs used to transmit the signal. Pipes from these extend to various parts of the building where the bells are placed. This arrangement would prove very useful, situated in the office of a factory or any large building, to which calls are frequent. Fig. 3 [a turntable with ticker-tape wrapped around it on the right, with some kind of pen or plotter device mounted to the left, into which a pipe runs from bulb A, an oval shaped ball, with talons of some kind hanging from it] shows the apparatus as used for a recording telegraph. The hammer, the end of which is furnished with a needle or pencil, instead of striking the bell, is made to touch or press against a constantly unwinding roll of paper. By slight, sudden compression of the bulb [A], a dot is made, while a steadier pressure produces a line - so that the ordinary morse alphabet can be easily used. /hmmm.../ Fig. 4 [a 'bulb' attached by a pipe to a bell] is a form of hand bell; A the bulb for communicating the impluse. The membrane which acts on the hammer, is contained in the letter box on the upper part of the bell."