The Electrical review Volume 6

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1878 Excerpt: ...practice, that we recognise distinctions in sound of a far more subtle character than that of pitch; and these finer distinctions have become so much more important for the purposes of human intercourse than the musical distinction of pitch, that many persons can detect the slightest variation in the pronunciation of a word who are comparatively indifferent to the variations of a melody. Now, the telephone of Professor Graham Bell is an articulating telephone, which can transmit not only melodies sung to it, but ordinary speech, and that so faithfully that we can often recognise the speaker by his voice as heard through the telephone. How is this effected? If the electrical part of the process consisted merely of alternations between current and no current, the receiving instrument could never elicit from it the semblance of articulate speech. What we want is not a sudden starting and stopping of the current, but a continuous rise and fall of the current, corresponding in every gradation and inflexion to the motion of the air, agitated by the voice of the speaker. The electric principle involved in Bell's telephone is that of the induction of electric currents discovered by Faraday in 1831. Consider first a conducting circuit, that is to say, a wire which after any number of convolutions returns into itself. Round such a circuit an electric current may flow, and will flow if there is an electromotive force to drive it. Consider next a line of magnetic force. This line, as Faraday first showed, is a line returning into itself, or, as the mathematicians would say, it is a closed curve. Now, if there are two closed curves in space, they must either embrace one another so as to be linked together, or they must not embrace each other. If the line of force as wel...