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G. E. Dering, in the year 1856, at Messrs. Searle's yard, on the River Thames; it was worked by a motor in which rotation was effected by magnets arranged within coils, like galvanometer needles, and acted on successively by currents from a battery.
Sounds and voices seemed to emerge as if from the very screen itself. There, before us, we saw a gambling joint operating in full blast. It was not the Forty-eighth Street resort. But it was strongly reminiscent of it. From the talking machine proceeded all the noises familiar to such a scene. Garrick had moved behind the screen that cut off our view of the galvanometer.
Suddenly, at 3:15 a.m., when exactly eighty-four miles of cable had been laid out, he who observed the galvanometer saw the speck of light glide to the end of the scale, and vanish! If a speck of fire had been seen to glide through the key-hole of the powder-magazine it could scarcely have created greater consternation than did the disappearance of that light!
But it is not so with the lines of magnetic force, for it matters not how much their power is increased they appear in no way to affect us. Their presence can, however, be made manifest to our eyes or ears by mechanical appliances. I have already shown you how this can be done by means of either a galvanometer or a telephone in circuit with a spiral wire.
If the two poles of the battery were connected by the long conductor of six hundred and sixty miles, the precaution having been taken to divide it into two portions of equal length, it was observed, on connecting the two free extremities of these two portions in order to close the circuit, that the galvanometer placed in the middle was the first to be deflected, whilst the galvanometers placed in the vicinity of the poles were not deflected until later.
The iron will now be removed, but the spirals left in the same position as before, and by increasing the speed of the reversals you see a higher deflection is given on the galvanometer. Now, on again interposing the iron plate the deflection falls to a little less than one-half, as before. I wish this fact to be carefully noted.
There was the Thomson reflecting mirror galvanometer and electrometer, while nearby were the standard cells by which the galvanometers were adjusted and standardized.
The strip expanded or contracted when exposed to heat or cold, and thrust itself upon the button more or less, thereby varying the electric current and deflecting the needle of the galvanometer to one side or the other. The instrument was said to indicate a change of temperature equivalent to one-millionth of a degree Fahrenheit.
The current is made to pass into the series of voltameters by means of a commutator, and its intensity is shown by a Deprez galvanometer. The voltameters, as shown in the diagram, are mounted in derivation in groups of two in tension. The spirits traverse them in two parallel currents.
The marker consisted of a light platinum wire, constantly emitting sparks from a Rhumkorff coil, so as to perforate a line on a strip of moving paper; and it was so connected to the movable needle of a species of galvanometer as to imitate the motions of the needle.
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