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"Now, my string galvanometer shows not only the effects of these moving and talking pictures on the emotions, but also, as it was really designed to do, the state of the heart with reference to normality. It shows to me plainly the effect of disease on the heart, even if it is latent in the subject.
The latter has curious magnetic properties; a magnetic needle brought alongside of it will be found placing itself at right angles to the wire bearing the current. On this principle is made the galvanometer for measuring the intensity of a current. Moreover, if a piece of wire is coiled round a bar of steel, and a powerful electric current pass through the coil, the bar will become a magnet.
He continued to work on the delicate apparatus with its thread stretched between the stationary magnets of the galvanometer, a thread so delicate that it might have been spun by a microscopic spider, so light that no scales made by human hands could weigh it, so slender that the mind could hardly grasp it.
Now then, as the electrical needle, moving across the copper plate, made electrical contacts of different degrees of strength, it worked a delicate galvanometer on the receiving end. The galvanometer caused a beam of light to vary to grow brighter or dimmer, according as the electrical current was stronger or weaker.
But Bell's greatest contribution to the search for wireless telegraphy was not his direct work in this field, but the telephone itself. His telephone receiver provided the wireless experimenters with an instrument of extreme sensitiveness by which they were able to detect currents which the mirror galvanometer could not receive.
One of the galvanometer wires was passed twice or thrice loosely round the brass axis of the plate, and the other attached to a conductor, which itself was retained by the hand in contact with the amalgamated edge of the disk at the part immediately between the magnetic poles. Under these circumstances all was quiescent, and the galvanometer exhibited no effect.
The sudden application of cold water or cold air to the surface of the nude body and the inhalation of cold air into the lungs have the effect of increasing the amount of electromagnetic energy in the system. Now let this person inhale suddenly fresh, cold outside air. At once the galvanometer will register a larger amount of electromagnetic energy.
On turning the handle of M the current is generated, and on closing the key K it circulates from the terminals of the machine through the bridge and the lightning-rod joined with the latter. The needle of the galvanometer is deflected by it, until the resistance in the box R is adjusted to balance that in the rod. When this is so, the galvanometer needle remains at rest.
"Yes, sir, I remember it well," responded Robin, "the room into which the conducting-wires from the ends of the cable are led to the testing-tables, on which are the curious-looking galvanometers and other testing machines." "Just so," returned Smith, pleased with his pupil's aptitude. "Well, on that table stands Professor Thomson's delicate and wonderful galvanometer.
By locally raising the temperature of an inconceivably fine strip of platinum serving as the conducting-wire in a circuit, the flow of electricity is impeded at that point, and the included galvanometer records a disturbance of the electrical flow.
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