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The high potential alternating current delivered by the secondary coil not only charges the spark gap electrodes which necessarily have a very small capacitance, but it charges the condenser which has a large capacitance and the value of which can be changed at will.
It prevents the current getting too strong at times and burning something out." "That's the way I understood it, too," said Herb. "And Dr. Dale said that in the larger sets they have what they call a variable condenser, so that they can get more or less damping action according to the strength of the incoming current waves." "I guess I get the idea," said Joe.
It was James Watt, mathematical-instrument maker, earning fourteen shillings a week, who brooded over his little model until the conception of the condenser burst upon him, as he was taking his Sunday afternoon stroll on Glasgow Green. Goodyear had a similar experience.
The problem was to reconcile these two conditions. At length the pregnant idea occurred to him the idea of the separate condenser. It came to him on a Sunday afternoon in 1765, as he walked across Glasgow Green. If the steam were condensed in a vessel separate from the cylinder, it would be quite possible to keep the condensing vessel cool and the cylinder hot at the same time.
The pipes of the cooling coils are much larger than those of the condenser, and as the fluid ammonia is forced in a fine spray into these large pipes and the pressure is relieved it expands or boils into the larger volume of vapour and in so doing extracts heat from the brine.
The experimenter will do best to take the wires at the start very long, and then adjust by cutting off first long pieces, and then smaller and smaller ones as he approaches the right length. A convenient way is to use an oil condenser of very small capacity, consisting of two small adjustable metal plates, in connection with this and similar experiments.
When a condenser is used in connection with experiments with such a coil, it should be an oil condenser by all means, as in using an air condenser considerable energy might be wasted. The wires leading to the plates in the oil should be very thin, heavily coated with some insulating compound, and provided with a conducting covering this preferably extending under the surface of the oil.
As for tuning, just as changing the length and the thickness of the prongs of a tuning fork varies the frequency with which it vibrates and, hence, the length of the waves it sends out, so, too, by varying the capacitance of the condenser and the inductance of the tuning coil of the transmitter the frequency of the electric oscillations set up in the circuit may be changed and, consequently, the length of the electric waves they send out.
Thus the theory of Lorentz, as well as that of Maxwell, leads us to foresee that if an insulating mass be caused to move in a magnetic field normally to its lines of force, a displacement will be produced in this mass analogous to that of which Faraday and Maxwell admitted the existence in the dielectric of a charged condenser.
This was the great object gained by James Watt, when, after various experiments, he gave up the idea altogether of condensing steam in its own or working cylinder, and then made use of a separate vessel, now called the condenser. The weight of steam is about 1800 times less than water.
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