"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. "When I made this discovery I was utterly astounded. I could not believe what I had seen was really true. It was too great a revelation of Nature to accept immediately and unhesitatingly." What Tesla had discovered, and soon announced to the scientific world, was the existence of stationary terrestrial waves of electricity, and its meaning was that an impulse sent into the earth was carried on these waves to the other side of the earth and rebounded without any loss of power. He had, in fact, discovered and turned to man's use the very heartbeats of our earth. "Whatever electricity may be," he continued, "it is a fact that it acts like a fluid, and in this connection, we may consider the earth as a great hollow ball filled with electricity." He goes on to explain that when an impulse is sent into this ball of electricity it proceeds to the opposite wall of the earth in waves and, finding no outlet it returns to the place it started, but in a series of waves exactly the opposite of the outgoing ones, so that the two cross and diverge at regular intervals as indicated in the diagram. [Illustration: A--Oscillator B--Opposite side of earth C--Waves in nodal and ventral intervals.]