phenomenon by supposing that the current flowed in both directions in the form of a wave, taking longer to go to one ball than to the other, so that there would be a difference of potential between the balls, and hence the spark. This was corroborated by the fact that when the connection to the induction coil was at a point symmetrical to the two balls, there was no spark, for then the wave arrived at both balls simultaneously. This experiment was the first to show the propagation of electric current in the form of waves, and Hertz calculated the time of such a wave running back and forth in the wire as the one-hundred-millionth of a second. The possibility of making such rapid oscillations opened up a whole new field of research, which has been greatly exploited in the last twenty-five years. Not only did Hertz show that the current in a wire was propagated in waves, but he also showed that the electromagnetic effects which are able to induce currents in other wires are also propagated across free space in waves. These waves traverse various obstacles, and are stopped only by conducting bodies. Many persons undoubtedly had the idea that these waves traveling through space might be used for signalling purposes, but it was due to the patience and pertinacity of Guglielmo Marconi that these waves, sent by Hertz a distance of a few score feet, might travel across the Atlantic Ocean and still retain the power of exciting a current in a wire properly set up to receive them. It was only in 1895 that Marconi first began his experiments on electric waves, and in the short time of seventeen years wireless telegraphy has become so important to commerce, not only in connection with the reception of intelligence from ships in distress, but for overland communication in certain remote regions of the earth that last summer a conference was held in London where representatives of over forty nations met to negotiate a treaty for the regulation of wireless communications at sea. I had the honor of being a delegate of the United States government to this conference, and during the five weeks of our proceedings, noting the caliber of the delegates sent by the different governments and the seriousness with which every detail was threshed out in the most diplomatic language, I became vividly impressed with the importance of wireless telegraphy to civilization, and again I thought of the work of Faraday in 1830, Maxwell in 1864, Hertz in 1887, as crowned with a success that they could never have foreseen.
Leaving the domain of electrical waves let us turn to another sensational discovery of seventeen years ago. We have seen that wireless telegraphy had been prepared for by the work of nearly three quarters of a century. In December, 1895, the world was startled by the announcement that Professor Röntgen, of Würzburg, had obtained from vacuum tubes in which an electric discharge was passing a new sort of rays, which, though invisible, would yet affect a photographic plate and also possessed the startling power of being able to pass through many
