Among the earlier experiments, which in themselves were wonderful enough, were the transmission of an electrical current through one wire without return, to light several incandescent lamps. Advancing further along the trail of wireless transmission of power, Tesla lighted the lamps without any wire connection between them and his transmitter.
The oscillator, though simple in its construction, is one of the most wonderful of all electrical devices. "You see," said Doctor Tesla, "all that is necessary is a high power alternating dynamo which generates a tremendous alternating current. For our oscillator proper, we make a few turns of a stout cable around a cylindrical or drum-shaped form, and connect its two ends with the source of electrical energy. Then, inside the big cable, or primary coil, we wind a lighter wire in spiral form. One end of the secondary coil is sunk into the ground and connected with a plate, and the other is erected in the air. When the current is turned on, our oscillator sends these electrical impulses into the earth and air—or, as the scientists say, into the natural media. These oscillations create electrical waves and affect any device that is tuned to them—but (and this is very important) no device that is not tuned to them."
Continuing the explanation of his high tension experiments, Tesla tells us that the awe-inspiring electrical display, of which there is a picture on page [136], was made by his oscillator which created an alternate movement of electricity from the earth into a hollow metal reservoir and back at a speed of 100,000 alternations a second. The reservoir is already filled to overflowing with electricity and as the current is sent back to it at each alternation the terrific force makes it burst forth with a deafening roar, as great as the heaviest lightning detonation. The electric flames shoot out in every direction searching for something on which they may alight, just as lightning sent from the clouds searches for a conductor upon which it may alight and escape into the earth. The induction coils in the picture are tuned to these tremendous electrical explosions, and the flames shoot direct to them, a distance of 22 feet.
The flames shooting from the coil of the oscillator pictured on page [164] were nearly 70 feet across, represented twelve million volts of electricity, and a current alternating 130,000 times a second. These hair-raising experiments created such electrical disturbances that it was possible to draw great sparks more than an inch long, from water plugs over 300 feet from the laboratory. One of the most marvellous things about these experiments is that any human being could remain in the vicinity. The absolute safety of these discharges when properly harnessed is well illustrated in the picture shown there as the man seen amidst the flames felt no ill effects from his experience, simply because this power was so thoroughly harnessed by the wizard Tesla, that it could go only to the device tuned to receive it. Every boy is familiar with stories of lightning striking one person, but yet leaving another person right next to him unharmed. Such is the action of Tesla's high tension currents, only he directs them by induction just as he wants them to go.
"But this is just like lightning!" exclaimed the boy.
"So it is," calmly answered Doctor Tesla with a smile. "I have often produced electrical oscillations even greater than the energy of lightning discharges."
These experiments were marvellous enough, but they were surpassed in a short time by his famous discovery of July 3, 1899, which showed him that he could send his wireless waves to the opposite side of the earth just as well as a hundred feet away.
This revelation, as the scientist calls it, came about through his study of lightning. The scientist had set up in his Colorado laboratory many delicate electrical instruments to register various different electrical effects. Tesla noticed, however, that strangely enough his instruments were just as violently affected by distant electrical storms as by nearby disturbances.
"One night when meditating over these facts," said Tesla, "I was suddenly staggered by a thought. The same thing had presented itself to me years ago; but I had then dismissed it as impossible. And that night when it recurred to me I banished it again. Nevertheless, my instinct was aroused, and somehow I felt that I was nearing a great revelation.
"As you know, it was on the third of July that I obtained the first definite evidence of a truth of overwhelming importance for the advancement of humanity. A dense mass of strongly charged clouds gathered in the west, and toward evening a violent storm broke loose which, after spending much of its fury in the mountains, was driven away with great velocity over the plains. Heavy and long persisting arcs formed almost at regular intervals of time. My observations were now greatly facilitated and rendered more accurate by the records already made. I was able to handle my instruments quickly, and was prepared. The recording apparatus being properly adjusted, its indications became fainter and fainter with the increasing distance of the storm, until they ceased altogether. I was watching in eager expectation. Sure enough, in a little while the indications again began, grew stronger, gradually decreased, and ceased once more. Many times, in regularly recurring intervals, the same actions were repeated, until the storm, as evident from simple computations, with nearly constant speed had retreated to a distance of about two hundred miles. Nor did these strange actions stop then, but continued to manifest themselves with undiminished force.