handsomely moulded arrangement for ordinary house installations for dynamos and accumulators, in carved work, with switches, instruments, and cut-outs, both solidly and tastefully arranged. Lampholders are of course illustrated. The Keys' Company have a speciality in incandescent lamps which they term the "Star," of which 5,000 a day are made. They are made for export only in England in 4, 6, 8, 10, 16, 20, 25, 32, 50, and 100 candle-power. The "Luna" arc lamp seems simple and easily adjusted; several arrangements of suspension gear are shown. Amongst the more particular specialties are the "Berlin" dynamos, electric motors applied to a greater variety of purposes, a very complete set of electric lighting arrangements for theatres including stage regulators, group regulators, temporary connections, supplementary lights, three-light stage effects, hanging lamps, etc. The catalogue of the very ingenious and manifold physical apparatus designed by Dr. Edelmann for research and laboratory purposes is a perfect mine of description of valuable and interesting instruments. Egremont.-Messrs. Nicholson and Jennings, electric engineers, Newcastle-on-Tyne, have been in communication with the Egremont Local Board as to electric lighting by water power, for which 40 brake horse-power would be required. At the last meeting of the Board the clerk said Mr. Boyd, the surveyor, supplied the following particulars, which were forwarded to Messrs. Nicholson and Jennings "I have, as requested, seen Mr. Head, the millwright, with reference to the power that can be got from the River Ehen at Egremont, and his opinion is that the paper mill in the parish of St. John's, belonging to Mr. Thos. Grice, of Bootle, and at present occupied by Jos. Ramsay, is the best and most suitable place. There is a good waterwheel ready, only requiring a little repair, and he calculates that in summer, at least 30 h.p. is available and in winter 60 h.p. On the 11th inst. I gauged the quantity of water going over the weir at this mill at 11 a.m., and found it to be about 3,000 cubic feet per minute, and there is 10ft. of fall at the wheel, which gives 34 h.p. On the same day at 12 noon I gauged the water passing at the Bleach Green weir and race, and found it to be 2,500 cubic feet per minute. This, with 10ft. head, would give 28 h.p. The water in the river had fallen considerably between 11 and 12 o'clock, which would no doubt account for the difference in the two gaugings. The Bark Mill would be of no use for the purpose intended, as it can only have the water when not required by the corn mill, and the present wheel is only 6 h.p. or 8 h.p. At Little Mill, by putting up a turbine, 25 h.p. in summer and 30 h.p. in winter might be got. From the above information, I think the paper mill is the most likely place, and could be fitted up at least cost." Messrs. Nicholson and Jennings, in reply to this, said the power was too near that required, 40 h.p., but the number of lamps might be reduced, each lamp taking 1 h.p. They added: "As long as you are sure of getting 40 actual horse-power, you would be quite safe. We would suggest your sending the particulars to Gilbert Gilkes and Co., late Williamson Bros., Canal Iron Works, Kendal. They have had very considerable experience in this class of work, and have put up some very efficient low-fall turbines, and will be only too glad to give you an opinion, and if necessary the price of a turbine." The following, from a letter from the Keswick Electric | Lighting Company, was also read: "The electric light is used in private houses, shops, and hotels, and is found quite satisfactory. The power is acquired by a Victor turbine, with 20ft. head of water giving 50 h.p., and steam power 50 h.p. in case of water running low either in dry or frosty weather. In front of the Keswick Hotel there is an arc lamp of 1,000 c.p., which is calculated to take 1 h.p. to supply. The front space has occasionally been used for a night drill of the volunteers." A committee was appointed to consider this correspondence, with power to call in professional assistance if necessary. correspondent of the Standard, that one of the first schools Liege University. It is a curious fact, says the Paris for teaching the science and applications of electricity to industry was opened at the University of Liège, the town to which the poor joiner's lad Gramme, born in 1826, at Jehay Bodegnée, Belgium, came to work, and at the same time to study geometry and mathematics at the free classes for adults. Had it not been for the knowledge he thus acquired at Liège, he would never have been able to understand the theories of the Italian savant Paccinotti, and to apply them in an invention which has made his name celebrated in every civilised country. One of the first schools of electricity was opened in 1883 at the same university. The initiative in this creation was taken by M. Montefiore-Levi, the Belgian senator and philanthropist, who is almost as well known throughout Europe and America as in his own country. In endowing the University of Liège with an electro-technical section, M. Montefiore-Levi had the double object in view of opening up a new and lucrative career to the students of the university where he himself had been educated, and of encouraging the electrical industries by facilitating the recruiting of their personnel, who require to have a thorough technical knowledge of electricity. He commenced by placing a sum of 100,000f. at the disposal of the Government for the preliminary cost of the purchase of the necessary instruments and materials, but since then he has gone on giving annually larger amounts, in proportion as the needs of the new school grew with its rapid development. The Government, on its side, furnished the buildings, but as the University of Liège was being rebuilt the electrical section was at first housed in modern constructions in the courtyard of the main buildings. This year it has been allotted a thoroughly appropriate building, containing workshops and laboratories. It is, indeed, so spacious that it has been possible to provide a separate laboratory for every two students of electricity. On this occasion M. Montefiore-Levi has given 150,000f. to provide the workshops and laboratories with all the necessary instruments and materials to enable students to make, not only the experiments requisite for their studies, but also experiments for new discoveries and inventions. The practical utility of the institution has been already amply demonstrated. All the students who have in any way distinguished themselves at it are sought after by the chiefs of the electrical industry. It would also be easy to give a long list of the useful inventions made by former pupils; but as imitation constitutes the most valuable praise, it will suffice to note that the Italian Government has followed the example set at Liège by creating a similar electrical school at the University of Milan, and by placing Signor Zurini, one of the former students of the Liège school, at its head. But though the electrical section of the Liège University owes its existence to M. Montefiore-Levi, its success and rapid development have been due to the untiring exertions of Prof. Eric Gérard, who has presided over it ever since it was created. M. Eric Gérard is a distinguished electrician, well known throughout Europe as having been the delegate of the Belgian Government at almost all the electrical congresses that have been held for many years past. He is a comparatively young man, having been born at Liège in 1856. When 22 years of age, he left the University of Liège and completed his electrical studies at the Belgian Ecole Supérieure de Télégraphie. M. Gérard has also written largely on electrical science. It was The electrolytic cell (F, in Fig. 1) which I used, consisted of a box formed of strips of window glass cemented together with marine glue. Its length was about 16 cm., breadth about 10 cm., and depth about 5 cm. It was divided traversely into two compartments of equal length by a glass partition cemented so as to be water-tight. Through the centre of this partition passed a tube whose length was different in different experiments. cemented at right angles to the partition, and its ends were open. At each end of the box were two electrodes, one of platinum (P) and one of zinc (Z), side by side, but not in contact. They were square with narrow strips projecting above the upper edge of the ends of the box. They were of approximately equal area, having edges about 4.5 cm. in length. Wires passed from the upper ends of the strips to brass binding screws fixed in and supported by blocks of solid paraffin. The wires from the zinc electrodes were of copper and had been soldered to the zinc without the use of acid. Those from the platinum electrodes were of platinum and had been welded to the electrodes. In both cases the wires were so thick that their resistance relatively to that of the electrolytic cell was small and might be neglected. From the binding screws thick copper wires passed to mercury pools in blocks of solid paraffin. From contiguous pools other wires passed to the ends C and D of the arms B C and A D of the bridge; and by connecting the proper pools by means of wires, the electrolytic cell might be joined up as an arm of the bridge either by means of the platinum or of the zinc electrodes. The electrodes were in all cases placed as close as possible to the ends of the box. I did not attempt to place them at exactly the same distance, but satisfied myself by preliminary experiments that slight differences in the placing of the electrodes made no appreciable difference in the resistance of the cell. With this cell (1) it was the same mass of liquid whose resistance was measured, whether the platinum or the zinc electrodes were used to connect it with the other arms of the bridge, and (2) there being a large mass of liquid in the cell, the tube being in the centre of this mass of liquid, the time intervening between the completion of a measurement of the resistance when the platinum electrodes were used and the completion of a measurement made with the zinc electrodes being a small fraction of a minute, and the cell * A paper read before the Royal Society, Canada. being approximately at the temperature of the laboratory, the temperature of the tube must have been practically the same at the times of both measurements. The only available box of resistance coils was a small one made by Stoehrer, of Leipzig. The coils were arranged so as to form three arms of a Wheatstone's bridge. Two of them contained two coils each of 100 and 10 Siemens units respectively. The third contained a number of coils ranging from 500 to 1 Siemens units. I had no galvanometer well adapted to the experiments. I therefore extemporised one by combining the core of one Thomson's dead beat galvanometers (made by Elliott) with a pair of coils from a Wiedemann's galvanometer (made by Stoehrer). Both these coils were differentially wound; and thus I could vary the resistance of the galvanometer by combining them in different ways. Nevertheless, I was not in any case able to give the galvanometer the resistance which it ought to have had to attain the maximum sensitiveness in the bridge. The lightest mirror which was available weighed, with the magnet attached, about 0.06 gramme, just about twice as much as that used by Mr. Ewing and myself in our experiments. The diameter of the mirror was about 9 mm. My extemporised galvanometer had another defect-viz., that the inner windings of the coils were about 4 cm. from the magnet. In making observations by the two methods, I in all cases first used the method under test, the cell being connected with the other arms of the bridge by means of the platinum electrodes, and immediately afterwards I determined the resistance with the cell connected up by means of the zinc electrodes. In this way I avoided bias. I varied the resistance of the cell by changing the strength of the solution, or by introducing short glass rods into the tube, or by using tubes of different lengths. The resistance of the cell was in these ways made to vary from about 100 to about 4,000 Siemens units. It would be useless to give the values of the resistance which the cell was found to have in the different observations made, as these values have no permanent importance. The general results were as follows: 1. As was to be expected, the resistance was almost invariably found to be greater when determined by the method under test than when determined by the other method. 2. When the resistance of the electrolytic cell was great say from 3,000 to 4,000 units, its value as determined by our method differed from its true value, as given by the use of the amalgamated zinc electrodes, by from 0.1 to 0.4 per cent. There was rarely so great a difference as 0.4 per cent., and in many cases the differences were less than 0.1 per cent. When, however, the resistance of the cell was small, say from 100 to 200 units, the differences were much larger, amounting even in some cases to 6 and 7 per cent. This unsatisfactory result, however, was clearly due to the fact that my box of resistance coils was so small that when the electrolytic cell had a small resistance I could not sufficiently reduce the current flowing through it without so increasing the resistance of the battery as to diminish seriously the sensitiveness of the bridge. The best test of the method under consideration, therefore, is given by the observations above referred to, with the cell so constructed as to have a high resistance. The agreement of these observationss seems to me to be very satisfactory, especially when we consider that, as pointed out above, the galvanometer with which the observations were made was so seriously defective. With galvanometer of proper construction, the error would undoubtedly be reduced to a still smaller magnitude. It requires to be reduced only to 0.054 per cent. to become as small as the difference found by Kohlrausch and Grotrian † between the resistance of a tube of zinc sulphate solution as determined by their admittedly satisfactory method and as determined by the use of amalgamated zinc electrodes. a * I think, therefore, we may conclude that the galvanometer has already been constructed by the aid of which the method under consideration may be applied to give Magnet-mirrors are now made I believe with moments of inertia of only 6.108 C.G.S. units. The one I used had a moment of inertia of 2400·10 C.G.S. units. +"Pogg. Ann.," Bd. cliv. (1875), p. 10. of the current. This is one of the most delicate of all the operations to be carried out on a central distributing system. At the places where the cables from the customers' houses are joined to the distributing mains it is usual to enclose the junctions within cast-iron chambers, termed serviceboxes. Figs. 21 and 22 allow the operations to be understood. The connection between two cables is made by a piece of copper (Fig. 22) having two collars between two clamps, of which the extremities of the cables to be connected are gripped by means of two bolts or screws. The conductors, M and N, which it is desired to attach to the branches, P and Q, are bared for a short length, m, n, p, and q. These parts are gripped by the connectors and screwed up tightly, after which an insulating substance is poured in, filling up the lower part of the cast-iron box-which, in most cases, is in two parts-and then the whole chamber is closed by a screw-down lid. The service mains coming laterally from the box pass through a sort of stuffing-box (Fig. 26). In this latter figure, the lateral wall is represented at A; a truncated opening is formed therein, into which is introduced an indiarubber plug, B, compressed by a screw-plate, C. Figs. 23 to 26 show the various forms of boxes, the construction of which is all upon the same principle. Every precaution is taken to ensure perfect watertightness in all the different parts. (To be continued.) EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICATION TO METHODS OF ARTIFICIAL ILLUMINATION.* BY NIKOLA TESLA. (Concluded from page 161). The ideal way of lighting a hall or room, would, however, be to produce such a condition in it that an illuminating device could be moved and put anywhere, and that it is lighted, no matter where it is put, and phenomena mentioned, one may observe that any insulated conductor gives sparks when the hand or another object is approached to it, and the sparks may often be powerful. When a large conducting object is fastened on an insulating support, and the hand approached to it, a vibration, due to the rythmical motion of the air molecules, is felt, and luminous streams may be perceived when the hand is held near a pointed projection. When a telephone receiver is made to touch with one or both of its terminals an insulated conductor of some size, the telephone emits a loud sound; it also emits a sound when a length of wire is attached to one or both terminals, and with very powerful fields a sound may be perceived even without any wire. very How far this principle is capable of practical application the future will tell. It might be thought that electrostatic effects are unsuited for such action at a distance. Electromagnetic inductive effects, if available for the production of light, might be thought better suited. It is true the electrostatic effects diminish nearly with the cube of the distance from the coil, whereas the electromagnetic inductive effects diminish simply with the distance. But when we establish an electrostatic field of force, the condition different, for then, instead of the differential effect of both the terminals, we get their cojoint effect. Besides, I would call attention to the fact, that in an alternating electrostatic field, a conductor, such as an exhausted tube for instance, tends to take up most of the energy, whereas, in an an electromagnetic alternating field the conductor tends to take up the least energy, the waves being reflected with but little loss. This is one reason why it is difficult to excite tion. I have wound coils of very large diameter and of an exhausted tube, at a distance, by electromagnetic inducmany turns of wire, and connected a Geissler tube to the ends of the coil with the object of exciting the tube at a distance; but even with the powerful inductive effects producible by Leyden jar discharges, the tube could not be excited unless at a very small distance, although some judgment was used as to the dimensions of the coil. I have also found that even the most powerful Leyden jar discharges are capable of exciting only feeble luminous effects in a closed exhausted tube, and even these effects upon thorough examination I have been forced to consider of an electrostatic nature. without being electrically connected to anything. I have been able to produce such a condition by creating in the room a powerful, rapidly alternating electrostatic field. For this purpose I suspend a sheet of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal being preferably connected to the ground. Or else I suspend two sheets as illustrated in Fig. 30, each sheet being connected with one of the terminals of the coil, and their size being carefully determined. An exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere, even a certain distance beyond them; it remains always luminuous. In such an electrostatic field interesting phenomena may he observed, especially if the alternations are kept low and the potentials excessively high. In addition to the luminous "Lecture delivered before the American Institute of Electrical Engineers at Columbia College, New York, May 20. How, then, can we hope to produce the required effects at a distance by means of electromagnetic action, when even in the closest proximity to the source of disturbance, under the most advantageous conditions, we can excite but faint luminosity? It is true that when acting at a distance we have the resonance to help us out. We can connect an exhausted tube, or whatever the illuminating device may be, with an insulated system of the proper capacity, and so it may be possible to increase the effect qualitatively, and only qualitatively, for we would not get more energy through the device. So we may by resonance effect obtain the required E. M.F. in an exhausted tube, and excite faint luminous effects, but we cannot get enough energy to render the light practically available, and a simple calculation, based on experimental results, shows that even if all the energy which a tube would receive at a certain distance from the source should be wholly converted into light, it would Hence the hardly satisfy the practical requirements. |