Discoveries and Inventions of the Nineteenth Century

known to break down a structure that would have supported their mere weight many times over, because they were all marching together and with a step corresponding in time with the oscillatory period of the bridge. It is now always enjoined in the military orders that troops in crossing a bridge must “break step.” Another familiar illustration of the accumulation of small synchronous impulses is the experiment of singing into a glass goblet the note corresponding with its vibration period. The singer merely by sustaining this note for a short time often succeeds in shivering the glass into fragments. M. Tesla believes that he has already succeeded in agitating the earth’s ether to some extent; he does at least obtain flaming purple streamers passing into the air from one end of a coil, while the other is connected with the earth. These discoveries and theories appear likely to lead to many unforeseen results, valuable for both science and its applications, and such as may far surpass the expectations of those who take less enthusiastic views of the matter than M. Tesla and his friends do. The theoretical properties of the ether and the conditions of it, which are held capable of making it the scene and the medium of all the hitherto so-called ponderable and imponderable forces, have not been completely worked out. The experiments that have been already made show that disturbances of very different kinds may be propagated in the ether by undulations of any length from less than 160000th part of an inch, as in the case of violet light already spoken of, to the 1,200 miles attributed to certain electrical conditions. The foregoing sentences, describing the discoveries of Hertz and others, had not long been penned before it had become possible to announce that they had borne fruit in as extraordinary an invention as could have distinguished the close of an extraordinary century. It is the realization of what the most accomplished electrician would not long before have pronounced a dream—namely, wireless telegraphy. The general principle of it should not be obscure after the account of the “Hertzian waves”; but our space does not permit a description of details of its working out in a practical form by a young Italian electrician, Signor Marconi. We have already seen that a Geissler tube, when its circuit is properly attuned, can be lighted up by the magneto-electric disturbance propagated without material contacts, and this itself would constitute a method of signalling to a distance. On the same principle, a discharge may be determined by the “wave” between conductors in certain adjustable conditions of electric tension, and in this way local circuits may be brought into play, and ordinary telegraphic effects produced, as described in the following article. The actual apparatus to receive the ethereal impulses is extremely simple—merely a little fine metallic dust (nickel and silver) in a glass tube included in the resonator circuit by a wire at each end, touching the dust. This gathers together, or coheres (hence the apparatus is called the coherer), under the magneto-electric influence, a local battery discharge then passes, completing a circuit, and the dust has to be shaken loose again by a mechanical agitation. Marconi has been able to signal over a distance of forty-three miles. 547 Fig. 281.—Portrait of Professor Morse.