The practical telephone handbook and guide to the telephonic exchange (1906) (14756098335)

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:

s taken of the fact that the resistance of some substances,especially a preparation of selenium, is affected by light.At the transmitting station a parallel ray of light is arrangedto fall on a polished vibrating diaphragm, from which thelight is reflected on to another reflector at the receivingstation, which concentrates the light on to the preparedselenium, the latter being included in a circuit containing abattery and a Bell telephone receiver. As the transmitting 6o PRACTICAL TELEPHONE HANDBOOK diaphragm vibrates, its polished surface curves, and so causesthe amount of light which falls on the selenium cell to cor-respondingly vary, and its resistance to vary proportionately,the sound being thus reproduced in the receiver. Fig. 44gives a sketch of the arrangement. In Tainters Radiophone the same effect is producedby heat-rays, these being absorbed by carbon in the form oflamp-black, which is used in the place of the selenium in thePhotophone, the other arrangements being similar.

Text Appearing After Image:

iRROft Fig. 44.—Arrangement of Photophone These are instances of Wireless Telephony, of which muchhas been heard lately,- but of which no very practicableapplication has yet been made. The later systems are similarto the Photophone, but more elaborated. Dolbear in 1880 invented a Condenser receiver whichdepended for its action on the variation of the attractionbetween two plates separated by air. when the differenceof potential between them was varied. One plate forms thevibrating diaphragm, and the other is fixed. The former isconnected to earth or return wire, and the latter plate to theline wire, in the circuit with which is an ordinary carbon trans- HISTORY 61 mitter and a battery. Variations of potential are caused onthe line when the transmitter is spoken into, and these affectthe diaphragm of the receiving condenser. Telephonic Exchanges.—The telephone at first was usedalmost exclusively for private purposes, but very early itwas recognised by Mr Hubbard, the father-in-law

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1906

Northeastern University, Snell Library

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public domain