There is not the slightest intention on the part of the authors to detract in the least degree from the brilliant work of Hertz, but, on the contrary, to ascribe to him the honor that is his due in having given mathematical direction and certainty to so important a discovery. The adaptation of the principles thus elucidated and the subsequent development of the present wonderful art by Marconi, Branly, Lodge, Slaby, and others are now too well known to call for further remark at this place.
Strange to say, that although Edison's early experiments in "etheric force" called forth extensive comment and discussion in the public prints of the period, they seemed to have been generally overlooked when the work of Hertz was published. At a meeting of the Institution of Electrical Engineers, held in London on May 16, 1889, at which there was a discussion on the celebrated paper of Prof. (Sir) Oliver Lodge on "Lightning Conductors," however; the chairman, Sir William Thomson (Lord Kelvin), made the following remarks:
"We all know how Faraday made himself a cage six feet in diameter, hung it up in mid-air in the theatre of the Royal Institution, went into it, and, as he said, lived in it and made experiments. It was a cage with tin-foil hanging all round it; it was not a complete metallic enclosing shell. Faraday had a powerful machine working in the neighborhood, giving all varieties of gradual working-up and discharges by `impulsive rush'; and whether it was a sudden discharge of ordinary insulated conductors, or of Leyden jars in the neighborhood outside the cage, or electrification and discharge of the cage itself, he saw no effects on his most delicate gold-leaf electroscopes in the interior. His attention was not directed to look for Hertz sparks, or probably he might have found them in the interior. Edison seems to have noticed something of the kind in what he called the etheric force. His name `etheric' may, thirteen years ago, have seemed to many people absurd. But now we are all beginning to call these inductive phenomena `etheric.' "
With these preliminary observations, let us now glance briefly at Edison's laboratory experiments, of which mention has been made.
Oh the first manifestation of the unusual phenomena in November, 1875, Edison's keenness of perception led him at once to believe that he had discovered a new force. Indeed, the earliest entry of this discovery in the laboratory note-book bore that caption. After a few days of further experiment and observation, however, he changed it to "Etheric Force," and the further records thereof (all in Mr. Batchelor's handwriting) were under that heading.
The publication of Edison's discovery created considerable attention at the time, calling forth a storm of general ridicule and incredulity. But a few scientific men of the period, whose experimental methods were careful and exact, corroborated his deductions after obtaining similar phenomena by repeating his experiments with intelligent precision. Among these was the late Dr. George M. Beard, a noted physicist, who entered enthusiastically into the investigation, and, in addition to a great deal of independent experiment, spent much time with Edison at his laboratory. Doctor Beard wrote a treatise of some length on the subject, in which he concurred with Edison's deduction that the phenomena were the manifestation of oscillations, or rapidly reversing waves of electricity, which did not respond to the usual tests. Edison had observed the tendency of this force to diffuse itself in various directions through the air and through matter, hence the name "Etheric" that he had provisionally applied to it.
Edison's laboratory notes on this striking investigation are fascinating and voluminous, but cannot be reproduced in full for lack of space. In view of the later practical application of the principles involved, however, the reader will probably be interested in perusing a few extracts therefrom as illustrated by facsimiles of the original sketches from the laboratory note-book.
As the full significance of the experiments shown by these extracts may not be apparent to a lay reader, it may be stated by way of premise that, ordinarily, a current only follows a closed circuit. An electric bell or electric light is a familiar instance of this rule. There is in each case an open (wire) circuit which is closed by pressing the button or turning the switch, thus making a complete and uninterrupted path in which the current may travel and do its work. Until the time of Edison's investigations of 1875, now under consideration, electricity had never been known to manifest itself except through a closed circuit. But, as the reader will see from the following excerpts, Edison discovered a hitherto unknown phenomenon--namely, that under certain conditions the rule would be reversed and electricity would pass through space and through matter entirely unconnected with its point of origin. In other words, he had found the forerunner of wireless telegraphy. Had he then realized the full import of his discovery, all he needed was to increase the strength of the waves and to provide a very sensitive detector, like the coherer, in order to have anticipated the principal developments that came many years afterward. With these explanatory observations, we will now turn to the excerpts referred to, which are as follows: