. The telephone system of the British post office. A practical handbook . an exceedingly doubtful point. An explanation of the Principle of Action. 15 action lies in the fact that these loose contacts vary in resistance whenshaken by sound waves which are directed towards them—, theresistance of the arrangement varies in exact synchronism with thesound waves. Now, whether the explanation of the phenomenon lies inthe fact that when the joints are shaken the pressure on the nails is varied,and that, therefore, the resistance is varied, is somewhat doubtful, Thenails are not very efficient as
. The telephone system of the British post office. A practical handbook . an exceedingly doubtful point. An explanation of the Principle of Action. 15 action lies in the fact that these loose contacts vary in resistance whenshaken by sound waves which are directed towards them—, theresistance of the arrangement varies in exact synchronism with thesound waves. Now, whether the explanation of the phenomenon lies inthe fact that when the joints are shaken the pressure on the nails is varied,and that, therefore, the resistance is varied, is somewhat doubtful, Thenails are not very efficient as a transmitter, but such sounds as the tickingof a clock and the pitch of a note are reproduced, but the timbre is Hughes experimented with various substances, but finally foundthat carbon acted far better than any other substance. The most commonform of carbon instrument is shown in Figure 7. It consists of twocarbon blocks, between which is fitted a third carbon rod with taperingpoints. The carbon pencil is fitted loosely, touching both blocks. Sound. Figure 7. is perfectly reproduced by this instrument, notwithstanding its simple andprimitive look. The question now arises—Why should carbon behave somuch better than iron ? Shelford Bidwell investigated this subject, andcame to the conclusion that the effect was not solely due to the improve-ment and deterioration of the electrical contact between the twoconductors. The electrical resistance of carbon, unlike that of all metals,decreases when the temperature is increased. The passage of a currentthrough carbon decreases its resistance by increasing its increase of temperature is obviously greatest at the points of contactwhere the resistance is greatest. Let us consider what would take placewhen the contacts were slightly shaken apart by a sonorous , the contact is rendered worse, and the current is thereby reduced,therefore the temperature at the points of contact is reduced.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjecttelepho, bookyear1901
