File:The practical telephone handbook and guide to the telephonic exchange (1906) (14733256506).jpg

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

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to corresponding soundwaves. Liquid Barretter.—A receiver which has been much used byProfessor Fessenden is known as the liquid or electrolyticbarretter. This instrument is a small cylinder containing aconducting liquid, such as nitric acid, immersed in which is ametal diaphragm having a very small hole in the centre, oppositewhich hole is fixed a very finely pointed platinum wire aboutjVoo* ^ia. connected to the collecting aerial. The receivedwaves act upon the layer of liquid lying between the fine pointand the rim of the small hole in the diaphragm, causing theresistance to vary in proportion to the intensity of the waves. 542 PRACTICAL TELEPHONE HANDBOOK The barretter is shunted by a circuit containing a battery andan ordinary telephone receiver as shown in Fig. 492. The varia-tions in resistance produced by the varying strengths of theelectro-magnetic waves cause a reproduction of the originalsound waves in the telephone. It is claimed that this receiver, having a resistance of
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Fig. 492.—Barretter Receiving Circuit, Fessendens System 2500 ohms, will respond to notes of 5000 vibrations per second,to a high-frequency voltage of 000015 volt or to a high-frequency current of 0-00006 milliampere. FessenderCs Thermal Barretter has also been used as a receiverwith good results. This is made up like a small carbon fila-ment electric lamp, but in place of carbon a very short length ofplatinum wire, drawn down to a diameter of only 06 of a milis used. The electric oscillations from the receiving aerial aresent through several of these barretters, which are connected inparallel with a telephone receiver and a source of small electro-motive force. Variations of resistance caused by the heatingof the fine wire by the received oscillations cause the repro-duction of the sounds in the telephone. Such receivers of electric waves as those just described are current operated receivers and act continuously, as con- WIRELESS TELEPHONY 543 trasted with voltage operated receive

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