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When the galvanometer shows the desired deflection, the needle, T, will indicate upon the dial, in decimal fractions of an inch, the exact distance through which the strip has been moved.
But if this smaller spiral be placed at a different angle to the larger one, it is, as you observe by the deflection of the galvanometer, again affected. This experiment is analogous to the one illustrated by diagram 6, which represents the result of an experiment made to ascertain the relative strength of capability or producing inductive effects of different parts of a straight electro-magnet.
Abandoning the Morse instruments and the high voltage, recourse was then had to Professor Thomson's instruments, which proved entirely effective with ordinary battery current. Because of the effect of induction the current is much delayed in traveling through a long submarine cable and arrives in waves. Professor Thomson devised his mirror galvanometer to meet this difficulty.
"Back of this screen," he went on, indicating it in the corner of the room, "I have placed what is known as the string galvanometer, invented, or, perhaps better, perfected by Dr. Einthoven, of Leyden.
With such an instrument as the above, Edison demonstrated the existence of heat in the corona at the above-mentioned total eclipse of the sun, but exact determinations could not be made at that time, because the tasimeter adjustment was too delicate, and at the best the galvanometer deflections were so marked that they could not be kept within the limits of the scale.
"This expectation was confirmed; for on substituting a small hollow helix, formed round a glass tube, for the galvanometer, introducing a steel needle, making contact as before between the battery and the inducing wire, and then removing the needle before the battery contact was broken, it was found magnetized.
But I guess we can solve the problem. Did you bring me the galvanometer?" "Yes, and all the other things," and the young inventor proceeded to take the articles from the bundles he carried. Mr. Swift looked them over carefully, while Tom walked about examining the submarine, for such was the queer craft that was contained in the shed.
In 1870 the siphon recorder, for tracing a cablegram in ink, instead of merely flashing it by the moving ray of the mirror galvanometer, was introduced on long cables, and became a source of profit to Jenkin and Varley as well as to Sir William, its inventor. In 1873 Thomson and Jenkin were engineers for the Western and Brazilian cable. It was manufactured by Messrs.
After a galvanometer deflection has been obtained through the expansion or contraction of the strip by reason of a change of temperature, a similar deflection is obtained mechanically by turning the screw, S, one way or the other. This causes the vulcanite strip to press more or less upon the carbon button, and thus produces the desired change in the resistance of the circuit.
It was shrilling in a thin scream of terrific speed, a speed that should have torn its windings to fragments under the lash of centrifugal force. Contentedly it said throatily. "Settled." The galvanometer spoke again in its peculiar harsh voice. "Therefore, move." Abruptly, without apparent reason, the stubborn relay clicked open.
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