The practical telephone handbook and guide to the telephonic exchange (1906) (14752935281)

Identifier: practicaltelepho00pool (find matches)

Title: The practical telephone handbook and guide to the telephonic exchange

Year: 1906 (1900s)

Authors: Poole, Joseph

Subjects: Telephone

Publisher: New York, Macmillan Co.

Contributing Library: Northeastern University, Snell Library

Digitizing Sponsor: Boston Library Consortium Member Libraries

Text Appearing Before Image:

f Hughes micro-phone. Edisons Loud-Speaking Receiver.—This was a very inter-esting instrument, and was much used at one time. It wasbased on the fact discovered by Edison, and utilised by himfor the construction of a telegraphic instrument, that thefriction between a metal and a substance subject to electro-lytic action varies in proportion to the strength of a currentpassing through the points of contact. The telephone re- 5* PRACTICAL TELEPHONE HANDBOOK ceiver constructed on this principle is shown in Fig. 43. Adiaphragm of mica, m, is mounted over an opening in a box,as shown, and a strip of platinum, c (only the end of whichis shown), is attached to its centre, and projects at right anglesfrom it. The end of c lies flat on the surface of a chalkcylinder, a, which is moistened with a solution of some easilydecomposed electrolyte, such as potassic iodide. The platinumstrip c and the metal supports of A are connected in circuitwith a battery and a carbon transmitter. On turning the

Text Appearing After Image:

Fig. 42 cylinder by the handle, w, so that the top moves away fromthe mica disc, the friction (which can be regulated by thescrew e) will cause the centre of the disc to be pulled inward.On a current passing, the friction at the contact will be reducedin proportion to the strength of the current, and the discwill partly recover its position. On passing the undulatorycurrents from a transmitter through the contact, and con-tinuously rotating the cylinder, the disc will be caused tovibrate and give out a sound similar to that directed to thetransmitter. In order to moisten the chalk cylinder, it wasarranged that on depressing a handle, G, a small absorbent HISTORY 59 roller, R, was lifted out of a reservoir, t, containing the electro-lyte solution, and brought into contact with the chalk. When properly adjusted, the instrument was a powerfulone, giving out sounds that could be heard all over a largehall. The tone of the instrument, however, being verynasal, left much to be desired, and

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1906

Northeastern University, Snell Library

http://commons.wikimedia.org/

public domain