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Three other sirens made to give vocal sounds or articulate speech. A device for projecting sound-waves to a distance without spreading and in a straight line, on the principle of smoke rings. A device for continuously indicating on a galvanometer the depths of the ocean.
Instantly a point of red light, surrounded by a vivid orange circle, appeared upon the screen, low down and to the left of center, and the timing galvanometer showed a wide positive deflection. "Hashed again!" growled Breckenridge. "I must be losing my grip, I guess. I put everything I had on that sight, and missed it ten divisions.
Moreover, these magnetically induced currents differ in no respects from other currents, for example, those produced by the voltaic pile, since, like the latter, they produce sparks, magnetize bars of steel, or deflect the needle of a galvanometer. In this manner Faraday solved the great problem. He had produced electricity directly from magnetism!
But Fortune seemed to be playfully testing the endurance of these cable-layers at that time, for, when the despair was at its worst, the tell-tale light reappeared on the index of the galvanometer, without rhyme or reason, calling forth a shout of joyful surprise, and putting an abrupt stoppage to the labours of the pickers-up!
Thermo-piles are interesting from a scientific point of view as a direct means of transforming heat into electricity. A sensitive pile is also a delicate detector of heat by virtue of the current set up, which can be measured with a galvanometer or current meter.
In the laying of light and power cables every joint, as made, should be tested for insulation with a Thomson galvanometer, as the insulation must necessarily be very high, and if one joint or section of cable is any weaker than another it may be very important in the future to know it. All tests must be made after the joint has cooled, for while hot its insulation resistance will be very low.
It is reported that on another trial the light from the star Arcturus, when focussed on the vulcanite, was capable of deflecting the needle of the galvanometer. When gelatine is substituted for vulcanite, the humidity of the atmosphere can also be measured in the same way. Edison's crowning discovery at Menlo Park was the celebrated 'phonograph, or talking machine.
Every department of mechanics was stimulated and benefited to an extraordinary degree. Copper for the circuits was more highly refined than ever before to secure the best conductivity, and purity was insisted on in every kind of insulation. Edison was intolerant of sham and shoddy, and nothing would satisfy him that could not stand cross-examination by microscope, test-tube, and galvanometer.
To these gifts of theory, electrical and mechanical, Thomson added a practical boon in the shape of the reflecting galvanometer, or mirror instrument. This measurer of the current was infinitely more sensitive than any which preceded it, and enables the electrician to detect the slightest flaw in the core of a cable during its manufacture and submersion.
The two most likely objections advanced against this conception by sceptical critics are as follows: " The mental vibratory motion, or vibratory waves, are not known to science, nor recorded on scientific instruments such as the galvanometer. What is the rate of such vibrations, and what is their general character?
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