Just about that time the newspapers reported that a young Italian student by the name of Marconi, while experimenting with Hertzian waves, had demonstrated that a Hertzian oscillator will send out electrical waves which will penetrate much longer distances when one of its sides is connected to earth. “Of course it will,” said I, “the grounded oscillator takes the earth into closer partnership.” When as a herdsman’s assistant on the pasturelands of my native Idvor I stuck my knife into the ground and struck its wooden handle, I knew perfectly well that the ground was a part of the vibrating system, and that the sound-producing stroke was taken up by the ground much better than when I struck the knife-handle without sticking the knife into the ground. But I also knew that unless the boy who was listening pressed his ear against the ground he would not hear very much. It was, therefore, quite obvious to me that the best detector for a Hertzian oscillator which is grounded must be another Hertzian oscillator which is also connected to the ground. Grounding of the sending and of the receiving Hertzian oscillators was in fact the fundamental claim of the Marconi invention. Marconi, in my opinion, was unwittingly imitating the young herdsmen of Idvor when, figuratively speaking, he stuck his electrical knives into the ground for the purpose of transmitting and receiving electrical vibrations, but the imitation was a very clever one; very obvious indeed as soon as it was pointed out, like all clever things.
Every now and then we are told that wireless signals might be sent some day to the planet Mars. The judgment of a former herdsman of Idvor considers these suggestions unscientific for the simple reason that we cannot get a ground on the planet Mars and, therefore, cannot take it into close partnership with our Hertzian oscillators. Without that partnership there is no prospect of covering great distances. A very simple experiment will illustrate this. Scratch the wood of a pencil and ask your friends who are sitting around a table whether they hear the scratching. They will say “No.” Put the pencil on the table and scratch it again; your friends will tell you that they can hear it faintly. Ask them to press their ears against the table and they will tell you that the scratching sound is very loud. In the third case the pencil, the table, and the ears of your friends are all one closely interconnected vibratory system. Every herdsman of Idvor would interpret correctly the physical meaning of this experiment. “If Marconi had waited just a little longer I should have done his trick myself,” I said jokingly to Crocker, and then I temporarily dismissed the matter from my mind as if nothing had happened. But I was fairly confident that my electrical resonators would some day find a useful application in this new method of signalling, and Crocker was even more hopeful than I was. I turned my attention to another problem and would have completed its solution, if my work had not been interrupted by the announcement of a most remarkable discovery made in Germany, I mean the discovery of the Roentgen rays.
I cannot describe the effects of this epoch-making discovery without referring again to great Helmholtz. It was due to his initiative that Hertz took up the research of electrical oscillations, which suggested to Marconi their technical application. This started a new technical art, wireless telegraphy, which developed into the radio art. Without Helmholtz, not only the experimental verification of the Faraday-Maxwell electromagnetic theory but also the radio art might have been delayed quite a long time. I shall point out now that the great discovery of the Roentgen rays also was due in a great measure to the initiative of Helmholtz.
While in Berlin I was conducting a research upon vapor pressures of salt solutions. For this purpose I needed the assistance of a clever glass-blower. A Herr Mueller was recommended to me by the people of the Physical Institute. I paid frequent visits to him, not only because I liked to watch his wonderful skill in glass-blowing, but also because he knew and entertained me often with the history of a remarkable physical research which had been carried out by Doctor Goldstein, a Berlin physicist, under the auspices of the German Academy of Sciences, Herr Mueller, the glass-blowing artist, assisting.
The motion of electricity through rarefied gases was first extensively studied in Germany in the fifties and sixties by several investigators. Hittorf was one of them, and I mention him here for reasons given later. The English physicists took up the subject a little later, and among them Crookes did the most distinguished work. His tubes with a very high vacuum gave brilliant cathode rays, first discovered by Hittorf, which produced among other things the well-known phosphorescence in vacuum tubes made of uranium glass. In spite of the surpassing beauty of the electrical phenomena in vacuum tubes revealed by Crookes’s experiments, no final and definite conclusions could be drawn from them toward the end of the seventies. But he was undoubtedly the first who correctly inferred that the cathode rays were small electrified particles moving with very high velocity. This inference proved to be of very great importance. In 1893 Lord Kelvin said: “If the first step toward understanding the relations between ether and ponderable matter is to be made, it seems to me that the most hopeful foundation for it is knowledge derived from experiment on electricity in high vacuum.” This was the very opinion which Helmholtz had formulated fifteen years earlier, and he persuaded the German Academy of Sciences to make a special grant for a thorough experimental review of the whole field of research relating to electrical motions in high vacua. Doctor Goldstein was selected to carry out this work. Mueller was his glass-blower. The most important result of this work was the discovery of the so-called Canal Rays, that is, motion of positive electricity in the direction opposite to the motion of negative electricity, the latter being the cause of the cathode rays. To get that result Mueller had to make innumerable vacuum tubes of all sorts of shapes. He told me that if all these tubes could be resurrected they would fill the house in which his shop was located. “But the grand result was worth all the trouble, and I am proud that I did all the glass-blowing,” said Mueller, with a triumphant light in his eyes, and his beaming countenance testified that he felt what he said. He was an artisan who loved his craft; and, judging from his remarkable knowledge of all the vacuum-tube researches which had been conducted up to the time of his co-operation with Doctor Goldstein, I inferred that he was a unique combination of the science and the art involved in the job which he was doing for Doctor Goldstein. Mueller was the first to arouse my interest in the results of vacuum-tube researches, and I always considered him one of my distinguished teachers in Berlin. New knowledge is not confined to the lecture-rooms of a great university; it can often be found in most humble shops, treasured by humble people who are quite unconscious that they are the guardians of a precious treasure. Mueller was one of these humble guardians.
The importance of Goldstein’s work was due principally to the fact that it brought into the field three other German physicists of great acumen. The first one was Hertz. Several years after he had completed his splendid experimental verification of the Faraday-Maxwell electromagnetic theory, he showed that the cathode rays penetrated easily through thin films of metal, like gold and aluminum foil, although these films were perfectly opaque to ordinary light. It was a novel and most important contribution to our knowledge of cathode rays, and would have been followed up by more additional knowledge if Hertz had not died on January 1, 1894, at the age of thirty-six. Helmholtz died several months later. Science never suffered a greater loss in so short an interval of time. Helmholtz met with an accident on the ship on his return trip from the United States in 1893. He never completely recovered, although he lectured at the University of Berlin until a few days before his sudden death in the mid-summer of 1894. Autopsy revealed that one side of his brain was and had been in a pathological state for a long time, but nobody had ever observed that his intellectual power had shown any signs of decay. It is a pity that he did not live another two years; he would have seen what he told me during his visit here he longed to see, and that is an electrified body moving at a very high velocity suddenly reversing its motion. That, he thought, might furnish a direct experimental test of the mobility of ether. The discovery described below furnished such a body.
Hertz’s work was continued and greatly extended by Professor Lenard of the University of Kiel. He would have undoubtedly reached the final goal if Roentgen had not announced, in December, 1895, that he, experimenting with Lenard vacuum tubes, had discovered the X-rays. This discovery marked the last step in the survey which Goldstein, under the initiative of Helmholtz, had undertaken some fifteen years before Roentgen had entered the field of electrical discharges in high vacua. It was a great triumph for German science. The science of electrical discharges in rarefied gases was started in Germany and in less than forty years it had reached there its highest point. It is a science which may justly be said to have been “made in Germany,” just as the science of radiation. It started a new and most remarkable era in physical sciences by extending the meaning of the Faraday-Maxwell electromagnetic theory.
SIR J. J. THOMSON (1856——)
No other discovery within my lifetime had ever aroused the interest of the world as did the discovery of the X-rays. Every physicist dropped his own research problems and rushed headlong into the research of the X-rays. The physicists of the United States had paid only small attention to vacuum-tube discharges. To the best of my knowledge and belief I was at that time the only physicist here who had had any laboratory experience with vacuum-tube research, and I got it by overtime work in the electrical-engineering laboratory of Columbia College. I undertook it because my intercourse with Mueller, the glass-blower of Berlin, directed my attention to this field of research, and particularly because I did not see that with the equipment of that laboratory I could do anything else. I decided, as mentioned above, to leave the field to Professor J. J. Thomson, of Cambridge, and to watch his work. When, therefore, Roentgen’s discovery was first announced I was, it seems, better prepared than anybody else in this country to repeat his experiments and succeeded, therefore, sooner than anybody else on this side of the Atlantic. I obtained the first X-ray photograph in America on January 2, 1896, two weeks after the discovery was announced in Germany.