Capacity Of Electric Conductors

Saturday, February 9, 1901
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222 Februtu'y9 1901 ELECTRICAL WORLD Arm ENGINEER. V°'»- XXXVU-, NG. 6- SYNTONIC AND MULTIPLE WIRELESS TELEGRAPHY. In the Digest of last week a concise account was given of the Slaby system of tuned and multiple wireless telegraphy, which system has recently been the subject of some successful experiments in Germany. As will be seen, the selective or syntonic feature consists first, in corresponding stations working with the same wave length, and in the employment at the receiving station of a vertical wire equal in length to a sub-multiple of the wave length agreed upon. By this means the, receiving instrument will not respond to wave signals sent from the same or other stations where this condition is not complied with. Moreover, by a certain disposition oi the aerial conductor it is made possible to receive simultaneously at a station messages of different wave length-this part of the system thus corresponding to multi- plex wire telegraphy. Another`part of the system consists in an "intensitier" arrangement corresponding to the local battery circuit of an ordinary telegraphic system, by means of which the potential of the received wave is increased, resulting in an increased effect on the coherer. The work of Prof. Slaby forms the most important contribution recently made to wireless telegraphy, and the system also appears to be a practical one. In tests made some weeks ago before the German Emperor, simultaneous messages were success- fully received irom two stations, one eight and the other two and one-half miles distant from the receiving point. The waves from the more distant station had to pass across the city of Berlin and were naturally attenuated by the high buildings and chimneys in its path, which effect, however, was counteracted by the application of the "intensitier" principle. The work of Dr. Slaby above referred to received considerable prominence in cable newspaper dispatches, and-not unexpectedly- Mr. Nikola Tesla now comes forward with a claim of priority. In a letter to the New York Sun, Mr. Tesla says he has read with "deep astonishment” the statements made in his lecture before the Em- peror by the Charlottenberg professor, who, moreover, had acknowl~ edged that he-Tesla-is the "father of wireless telegraphy." Mr. Tesla also expresses disappointment that Dr. Slaby does not give him credit “for a beautiful invention which he [Dr. Slaby] calls the ‘multiplier.’ " "Have I not tirst described this device," he says, “and given rules for its construction and attunement? Was I not the first to apply it to wireless transmission P" For obvious reasons we have not been able to keep pace with all the numerous newspaper ascriptions to Mr. Tesla of revolutionary discoveries in electrical science, which probably explains our ignorance of the claim that he is the “father of wireless telegraphy," or indeed that the art of wireless telegraphy has-in any manner benefited from his labors. If Mr. Tesla would do what may fairly be asked of a man of his prominence-prepare a paper for the American Physical Society or the American Institute of Electrical Engineers covering the work he has accomplished in this branch-we shall be able to repair our own seeming neglect in not laying before our readers hitherto the record which would entitle him to be called "the father of wireless telegraphy.” CAPACITY OF ELECTRIC CON DUCTORS. In our issue of last week we quoted from a letter over the signa- ture of Mr. Nikola Tesla in the New York Sun of Jan. 30, in which it is stated that the capacity of a lixed insulator conductor is not a fixed quantity, but varies with' the hour oi the day, with the season of the year, that it is inlluenced by moonlight, etc. lt is also intimated that in consequence of this newly discovered fact a large part of technical literature will have to be rewritten.` May we venture to express our doubts upon these propositions, with all due deference to Mr. Tesla. So'far as text books are concerned, they are only stepping stones, and not keystones, in the structure of our

Fesizuuv 9, I@I. ELECTRICAL WORLD AND ENGINEER iaith. The sooner they have to be cancelled, amended and rewritten, the healthier and more sturdy the growth of the science to which they relate. but the evolution of text books and of the knowledge they disclose must be like all other evolution, in a definite and order- ly manner, in obedience to certain rules. We have every reason to believe that the capacity of the con- densers in our laboratories is within certain small limits a dehnite and constant quantity. The capacity of aerial wires insulated on poles and supported many feet from the ground seems to be a sub- stantially constant quantity from day to day and year to year, pro- vided that the surface of the earth is uniformly conducting. It has long been known-though not, it would seem, by Mr. Tesla-that when the surface of the earth is dry and ill-conducting, the apparent capacity of single wires supported above it is less than when the earth is wet and well-conducting. If, therefore, Mr. Tesla refers to variations of capacity between a fixed aerial conductor and the ground due to variation in the conductivity of the surface soil, he is virtually repeating a known proposition. Concerning the variation in capacity of a conductor relatively to the earth with elevation above the earth, it is not a discovery that there must be a change of some sort in capacity. The experimental knowledge we possess concerning the capacity of very elevatedcon- ductors, is, however, so limited that there is room for valuable technical results to be observed in this direction, and if Mr. Tesla has made reliable observations of this character the science would awe him so much the more for their announcement. We hope that Mr. Tesla will publish any results which he may have obtained, in such form as may be available to electrotechnical workers, It is quite clear that not only is no substantial technical informa- tion imparted to electrical engineers by articles of the nature which Mr. Tesla communicates so frequently to the daily press, but also that it is impossible for an electrical engineer to judge from such ar- ticles of the validity of the conclusions which are therein reached. It is quite possible that the apparent capacity of very elevated conduct- ors might vary in a manner not generally appreciated or understood, and yet that the' capacity of the ordinary conductors in the neigh- borhood of good conducting ground should be as fixed and constant a quantity as has always been supposed.