THE PHYSICAL LABORATORY 115 



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 cur- 

 rent 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 propa- 

 gated 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 re- 

 ception of intelligence from ships in distress, but for overland communi- 

 cation in certain remote regions of the earth that last summer a confer- 

 ence 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 govern- 

 ment 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 sensa- 

 tional 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 an- 

 nouncement that Professor Rontgen, of Wiirzburg, 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 



