thing that it was ten years ago, save that improvements in manufacture have rendered the product somewhat more uniform. Chief among these we must reckon the almost universal use of the squirted cellulose filament and the introduction of the chemical method of final exhaustion. Various efforts have been made to introduce incandescent lamps of about double the usual voltage. The difficulties of construction of such lamps, their relatively low efficiency and the use with which an alternating distribution at the usual voltages is effected constitute ample reasons for the small use of these high voltage lamps; while the vigorous objections of the fire underwriters have discouraged any extensive exploitation of them. The greatest change of recent years in general lighting has been the introduction of the enclosed arc lamp, which has worked a revolution in indoor lighting at constant potential as well as in street lighting. It has on the whole stimulated incandescent lighting, however, by raising the common standard of brilliancy, and by aiding in the unification of service. Considerably more than half the arc lights in use are enclosed, the bulk of the open ones being used for street lighting by companies not yet quite ready to undertake re-equipment. Of the alternating arcs more than nine tenths are of the enclosed type, a result due almost to necessity. The introduction in recent years of series alternating arcs fed from constant current transformers is responsible for most of the use of alternating current arcs, and practically all such are enclosed. Through all these years of progress the incandescent lamp has held its own and has grown in relative popularity. The same virtues that gave it its start in life have kept its fortunes in the ascendant. With all its failings in points of efficiency it is to-day, as it was in the beginning, the best available illuminant in point of quality and general usefulness. Within very recent years determined efforts have been made to obtain other electric lamps of equally good qualities and of higher efficiency, but up to the present these efforts have not been crowned with success. The Nernst lamp, most admirable in some respects, is at its best in competition with the arc rather Vol. 7-11 than the incandescent lamp, and is still a rarity, not yet seriously to be considered in the grand total of electric illumination. The mercury arc, another recent candidate for lighting honors, has little yet to show in the way of results, and its color is so hopelessly bad that unless remedied by some very radical step, the lamp will entirely fail of material usefulness as a general illuminant. If the public could be educated up to the point of liking the color of the mercury arc, it would already have welcomed the incandescent gas mantle to the exclusion of nearly everything else. The incandescent lamp is then to-day as it has been all through its history, the mainstay of modern illumination so far as interior lighting is concerned. It may in due season be supplanted by something better, but that something will have to be equally steady and simple and convenient and good in color. At the present time there are nearly twenty million incandescents in lighting service from central stations in this country alone-how great a harvest from the seedtime of 1879! Electric lighting has won its way into the front rank of American industries, and there it is likely to stay. Its full history cannot be written apart from that of the country's industrial growth with which it has more than kept pace. THE TRANSMISSION OF ELECTRIC ENERGY WITHOUT WIRES. BY NIKOLA TESLA. [Nikola Tesla, electrician; born Smiljan, Lika, 1857; educated in the public schools of Gospich; graduated from Real Schule, Karlstadt, 1873; studied at Polytechnic school, in Gratz, to become a professor of mathematics, but later changed and completed the engineering course; studied languages and philosophy at Prague and Buda-Pesth; was for a time assistant in government telegraph engineering department, where he invented several improvements; afterwards became engineer for a lighting company in Paris; afterwards came to the United States and was employed by Edison company; later became electrician for the Tesla Electric Light company and established the principle of the rotary magnetic field embodied in the apparatus used in transmission of power from Niagara Falls; inventor of various forms of dynamos, induction coils, transformers, etc.] Copyright 1904 by McGraw Publishing Company Towards the close of 1898 a systematic research, carried on for a number of years with the object of perfecting a method of transmission of electrical energy through the natural medium, led me to recognize three important necessities: First, to develop a transmitter of great power; second, to perfect means for individualizing and isolating the energy transmitted; and, third, to ascertain the laws of propagation of currents through the earth and the atmosphere. Various reasons, not the least of which was the help proffered by my friend Leonard E. Curtis and the Colorado Springs Electric company, determined me to select for my experimental investigations the large plateau, two thousand meters above sea level, in the vicinity of that delightful resort, which I reached late in May, 1899. I had not been there but a few days when I congratulated myself on the happy choice and I began the task, for which I had long trained myself, with a grateful sense and full of inspiring hope. The perfect purity of the air, the unequaled beauty of the sky, the imposing sight of a high mountain range, the quiet and restfulness of the place-all around contributed to make the conditions for scientific observation ideal. To this was added the exhilarating influence of a glorious climate and a singular sharpening of the senses. In those regions the organs undergo perceptible physical changes. The eyes assume an extraordinary lim |