and the permanent installation commenced. From one point of view, however, it seems somewhat natural that Carlow should take the lead among Irish towns. If we mistake not, Prof. Tyndall, whose name stands in the front rank of scientific worthies of the nineteenth century, first saw the light "just a stone's throw away from Carlow's environs, in her twin borough-old Leighlin," and will be one of the first to recognise the suitability of electricity to assist in utilising the waste water power of the district. According to Mr. Brophy, in his "Carlow Past and Present," the town ought to be termed the "Athens of Leinster," because "it has more the appearance of a city than of an ordinary Irish country town"; its streets are not straggling and irregular; the leading streets converge from four different points on the exact centre, the public buildings assume classic styles of architecture, and so ongood reasons to an Irish author, but, like many other statements, hardly convincing. We must admit, however, that the streets are fairly favourable to electric lighting, much more so, indeed, than is the case in many old and in not a few modern towns. Again, the town is fairly compact, an advantage not to be despised when the cost of mains is considered. Returning now to our visit. Given a warm, sunny day, pleasant companions, pretty scenery, and what is more enjoyable than a river journey? One feature in connection with the Barrow was noticeable. There was absolutely no other traffic upon its waters, and weeds were rapidly blocking the stream-thanks to a strike in Dublin, whereby those who usually worked the barges, and those who cleaned the stream, were idly standing at the bridge, or to be found under worse conditions elsewhere. Arriving

cables are installed over about five miles of streets, and are carried on posts set up at the edge of the footpaths, and some of the lamps higher than the others carry the arc lamps. The lamps, in fact, are nearly 50ft. above the street level. They are of the Brockie-Pell type, some fitted with globes, and some with lanterns. Those of the lantern shape seem to find most favour.

The public lighting of the streets has hitherto been carried out by 100 oil lamps of 10 c.p. each, and costing the Town Commissioners £104 per year for a total light of 1,000 c.p. It is now carried out by 13 arc lamps of 1,200 c.p. each, and 40 incandescents of 16 c.p. each, giving a total light of 25,840 c.p., or 25 times the former amount, and for this the Commissioners pay £170 a year. The present plant provides, in addition to the public lighting, for about 1,200 incandescent lamps in shops and private houses, and these are charged at a fixed rate per annum, calculated to be about 5 per cent. less than the customer's former gas bill,

The transformers which transform the current from the high-pressure form, necessary for carrying it to a distance, to the low pressure of 50 volts at which it is utilised, are fixed upon conveniently selected posts at intervals throughout the town. No transformer is in any building or

Oil Insulators for carrying Line and Return.

at Milford, the dynamo-room, in the old mill belonging to Major Alexander, was visited. Here is an Elwell-Parker 50-kilowatt alternator with its exciter, driven by belts from a shaft driven by the huge waterwheel of the old mill. The waterwheel is about 15ft. diameter by 20ft. in length, and under present conditions all the power required can be easily obtained, but in flood time the tail rises till the head of water available is only about 5ft., so arrangements are rapidly approaching completion, when a couple of turbines will be available, and these, together with the waterwheel, which could still be used, would supply some 300 h.p. We illustrate the plan of the dynamo-room, which is fitted with the usual switchboard and measuring apparatus, with a transformer to run the lights required in the works. From the switchboard the mains run to an upper floor, leaving the mill high up, are carried across the river, and run, 20ft. high, on poles along the towpath of the Barrow river, the use of which has been granted at a nominal rent by the Barrow Navigation Company. Fowler-Waring cables are used, and, to make doubly sure, both line and return are carried on JohnsonPhillips oil insulators. The cables fulfil the Board of Trade requirements, which many people think too stringent. The current is generated at 2,500 volts, and transformed down to 50 volts for use. The loss in transmission is now found to be about 2 per cent., but the calculations have been made to allow of a loss of 10 per cent. when the whole of the public and private lighting is in full swing. The cables are, as we say, brought overhead into a small switchhouse in the centre of the town, where the controlling apparatus for the town lighting is situated, and from whence the circuits can be tested. The distributing

Street Lamppost, carrying Transformer.

private property, or in any way within reach of the public. This is an important element of safety.

The low-pressure system of mains consists of bare copper ropes or strands carried on porcelain insulators, and these are fixed partly on the same posts that carry the highpressure wires, and partly on the fronts of the houses.

Messrs. Gordon and Co. contend that in the ordinary system of placing transformers it is not profitable to supply a customer unles he will take 15 or 20 lamps, but by the system introduced into Carlow the small customer using one, two, or three lights is, pro rata, as good a customer as anybody else, and there seems to be much truth in this contention. We trust that experience will go to prove that many private residents will install a few lights when only a few are really required, so that the summation of these installations will lead to demand to the full capacity of the works.

This point is absolutely essential if electricity is ever to cease to be a luxury of the rich and to become the poor man's light.

Messrs. Gordon claim that they have solved the question, and have brought the light within the reach of anyone who is able to afford gas.

The machinery was started for the first time a few minutes after midnight on Wednesday, June 24 and has

run without a hitch or difficulty from the moment of starting.

Messrs. Gordon's engineer-in-charge, Mr. Meredith (son of Mr. George Meredith, the well-known novelist), together with an English foreman, has carried out the work entirely by local labour. The whole of the erection of poles, placing of machinery, wiring of houses, etc., has been done by the ordinary labourers of the district, of whom between 40 and 50 have been employed ever since the work was commenced in December last.

We have in a previous issue referred to the inaugural banquet, and it only remains to add that the various deputations seemed highly pleased with the installation, and went away with the view to use their best endeavours to get the light introduced into the various towns represented by them.

It is difficult to calculate what effect this introduction of a new enterprise may have upon the future political and social development of Ireland.

It is expected that the next town that will be completed by Messrs. Gordon will be Larne, the rising sea port and holiday resort near Belfast, the importance of which is rapidly increasing since the opening of the new Larne and Stranraer mail route, a portion of which will be lighted up on August 1st.

Negotiations are in progress with various other important

towns.

NIBLETT'S SOLID ACCUMULATOR.

Of late years many attempts have been made to overcome that inherent weakness of all known electric storage batteries--viz., the warping, buckling, and rapid disintegration of its elements-but so far but little real advance seems to have been made. The want of a really good, inexpensive, mechanically strong cell of high capacity and small weight has been keenly felt by all those who have been associated with electric tramcar work, electric launches, and the almost innumerable other purposes where some form of portable means of storing electrical energy is an essential. The many suggested plans for producing locomotion by means of electricity are just now attracting much attention, and there is every prospect that at no very distant period this branch of electrical engineering will become fully as important as the electric lighting industry is at present. Much may be said in favour of the suggested methods of conveying the electrical energy through overhead conductors, the utilisation of the road rails, or separate insulated high-conductivity conductors as the leads, or the mode of "picking up" the current from underground mains. If, however, a secondary battery can be produced which shall be capable of withstanding the excessive electrical strain incidental to a rapid and irregular rate of discharging, and the mechanically disruptive effect which always seems to attend concussion and jolting, and greatly tells upon all forms of accumulators when used for traction purposes, then the self-contained storage battery system would be found to compare most favourably with any of them, both in point of simplicity and economy.

There can be but little doubt that there is at the present time an enormous field for a cell which will combine large capacity with small weight, and great mechanical solidity. Some little time ago great hopes were entertained that the solidity problem had been solved by the introduction of Dr. Schoop's solid electrolyte. In this country some practical trials have been made with Mr. BarberStarkey's method of forming solid cells, by substituting for the fluid electrolyte a mixture of wood sawdust and plaster of Paris, which, when set, was moistened with dilute sulphuric acid. In America, the semi-sclid batteries of Messrs. Hatch and Wiswell, and Mr. Pumpelly, are said to be doing good work. One great drawback to the employment of a viscous, gelatinous, or solid porous electrolyte resides in the fact that when such substances are interposed between the plates no free circulation of the liquid is possible. In all secondary cells the activity of their elements depends entirely upon chemical action; and as the electrolyte is the medium through which all the

a

necessary reactions take place, it seems highly probable that anything which prevents its free access to the active material, or in any way impedes its circulation, must be detrimental, and lead to loss of efficiency and capacity. Some new forms of mechanically solid storage cells have recently been devised by Mr. J. T. Niblett, which, in addition to their absolute mechanical solidity, possess the advantages of simplicity of construction, high current capacity, and the property of being able to withstand very high rates of charge and discharge-most important points in storage cells when used for traction or portable purposes. The new cell in its simplest form is of the Planté plain lead type, but the same method of construction has been applied to the lead, lead-peroxide, lead-zinc, copper-zinc, and many other combinations with the acid or alkaline electrolytes. Each element consists of a highly cellulous mass of material which is capable of absorbing sufficient quantity of the liquid electrolyte for the due performance of all the possible and necessary chemical reactions. Between each electrode is placed a thin highly porous inert diaphragm, which is found not to materially increase the internal resistance, and which serves to complete the solid character of the cell. In one form an outer metallic containing chamber constitutes one electrode of the couple, and when the cells are joined up to form a battery, an extension of one side of the metal case serves as the electrode of the opposite polarity in the following cell, and so on throughout the series. The cellulous metal which constitutes the elements is prepared by a very simple mechanical process, and it is made electrically active either by the ordinary "forming" operation, by chemical means, or in some cases by the electrolytic deposition of chemically spongy metal. The method of formation will naturally depend upon the nature of the materials which constitute the cell.

Owing to the cellulous nature of these elements the liquid contained within their pores is continually circulating throughout the mass, the slight evolution of gas which is continually occurring both during the charge and discharge being quite sufficient to effect this. Any expansion of the elements occurring in the formation or working, which in other batteries too frequently results in the buckling and disintegration of the plates, and consequent troubles due to shortcircuiting, has practically no effect on a battery constructed according to the improved plan, as the whole is solidly contained within a rigid casing, which may be of any strength requisite, and the elements are incapable of displacement. The cellular nature of the electrodes gives them the peculiar property of self-regulating their own internal resistance. If the cell be charged at a too high rate, or when it is on the point of receiving the full complement of its charge, the gas generated tends to drive the electrolyte from the pores of the electrodes, and itself to remain imprisoned therein, thereby greatly increasing the internal resistance. In the same way, as a discharge proceeds the occluded gas re enters into chemical combination, and allows the liquid to refill the pores, and thereby exposes more active surface. As a means of inserting a hydrometer to test the density of the electrolyte, one or more perforated metal tubes extend throughout the whole depth of the active material, the tubes being of such dimensions as to freely allow of the insertion of the density testing apparatus. By the adoption of Mr. Niblett's plan, any of the ordinary forms of electrodes, whether of the plain lead, the grid, or the compressed slab types, can readily be made up into the solid form without in any way decreasing their current capacity per pound of complete cell, or their general efficiency.

So far the new battery, in its commercial form, has not been put to any prolonged practical trials, but we understand that a battery, consisting of 12 experimental cells were constructed over two years ago, and these have been purposely subjected to much bad and improper treatment, the result being that at the present time the whole of the cells are in excellent condition, and show no signs whatever of deterioration. In the absence of the necessary data as to capacity, efficiency, internal resistance, and the E.M.F.'s of the various combinations, we are, of course, quite unable to say how these cells compare with other well-known forms; but we are assured that experiments have proved that they compare most favourably, both in point of capacity, efficiency, and weight, with any cell yet produced

There can be no doubt that an inexpensive, light, and mechanically solid storage battery is a great desideratum, as there is at the present time a large and increasing demand for portable batteries suitable for such purposes as safety lamps, such as are used in coal mines, petroleum ships, gunpowder mills, gas works, etc. For tramcar propulsion, electric buses, electric launches, and submarine boats, and also for supplying the energy for train, carriage, and other forms of portable electric lighting, a battery capable of withstanding a considerable amount of jolting and rough treatment is much needed. A large number of portable storage batteries are now being employed both in the army and navy, but it is found that the rough treatment they receive seriously tell upon them.

As the battery we have just described seems to possess most of the essentials of a really good portable medium for storing electrical energy, it should be found of much service for the purposes we have enumerated.

In the new cell the whole of the active material is held solidly in position, and cannot move, and it therefore follows that the necessary current collectors may be very light, and in practice it is found that a very high current capacity per pound of complete cell may safely be obtained. One of the small cells we were shown was constructed for traction purposes, and as an indication of its capabilities the following data is given:

Best rate of discharge

Working current capacity

...

5in. 33in.

1 in.

2lb. 10oz.

1 to 2 amperes. 0.5 to 10 ampere. 3 ampere-hours.

Working energy capacity 12 watt-hours. These batteries were of the Planté type, and were simply formed by the ordinary process of charging and reversing. Naturally, as the size and capacity increases the comparative weight decreases. The cells shown to us consisted of a light leaden chamber, forming the negative pole, and these were firmly cemented into a strong wooden outside case. Special terminals, which are really elongations of the electrodes, are used. As an example of the mechanical solidity of the Niblett accumulator, the cell exhibited was thrown with some violence several times to the floor without suffering the least injury.

ELECTRIC LIGHTING IN LONDON.

Mr. R. Percy Sellon, M.I.E.E., at the last weekly meeting of the Balloon Society in St. James's Hall, gave an address on the above subject. He gave a sketch of the early history of electric light, and of the first Electric Lighting Act of 1882. Six years later the Electric Lighting Act of 1888 was passed, extending the period of tenure from 21 to 42 years, which, though far from placing electric lighting on the favourable conditions under which gas started, has resulted in an immense development. Nine companies and one local authority are now supplying electricity over the greater part of London, with an aggregate capital of £3,000,000, and already some are paying dividends. The equivalent of half a million lamps of 8 c.p. are now distributed, and additions are being rapidly made; some of the largest have trebled and quadrupled their production within the last 12 months. Mr. Percy Sellon described very fully the contract entered into between the Commissioners of Sewers of the City of London and the Brush and the Laing-Wharton Companies, which con

stitutes a scheme of an unusually comprehensive character. As regards public lighting, it is the first instance in this country where a public authority has courageously determined to wholly abandon other illuminants in its streets, large and small, in favour of electric lighting. Arc lamps to be placed in the main thoroughfares, and incandescent lamps in the side streets. Then under an extensive scheme of private lighting, current will be supplied to offices, warehouses, and business premises. Upon the question of cost, Mr. Sellon expressed his opinion that the adoption or otherwise of electric light would turn less upon a question of actual cost in pounds, shillings, and pence per quarter than upon a higher standard of comfort among the people. The fact that the City authorities are willing to pay more than twice as much for public lighting by electricity as they have paid previously for gas, points to this conclusion. Mr. Sellon then dealt with the question of danger to life and fire risk, showing that the Board of Trade and fire office rules had rendered these less than than those of gas or oil. At the conclusion of the paper a resolution was carried that it was not desirable that the Legislature should unduly interfere with the development of the electric lighting industry.

EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICATION TO METHODS OF ARTIFICIAL ILLUMINATION.*

BY NIKOLA TESLA.

(Continued from page 64.)

But of all the views on nature, the one which assumes one matter and one force, and a perfect uniformity throughout, is the most scientific and most likely to be true. An infinitesimal world, with the molecules and their atoms spinning and moving in orbits, in much the same manner as celestial bodies, carrying with them and probably spinning with them ether, or in other words, carrying with them static charges, seems to my mind the most probable view, and one which, in a plausible manner, accounts for most of the phenomena observed. The spinning of the molecules and their ether sets up ether or electrostatic strains; the equalisations of ether tensions sets up ether motions or electric currents, and the orbital movements produce the effects of electro and permanent magnetism.

tensions

About 15 years ago Prof. Rowland demonstrated a most interesting and important fact-namely, that a static charge carried around produces the effects of an electric current. Leaving out of consideration the precise nature of the mechanism which produces the attraction and repulsion of currents, and conceiving the electrostatically charged molecules in motion, this experimental fact gives us a fair idea of magnetism. We can conceive lines or tubes of force which physically exist, being formed of rows of directed moving molecules; we can see that these lines must be closed; that they must tend to shorten and expand, etc. It likewise explains in a reasonable way the most puzzling phenomenon of all, permanent magnetism, and, in general, has all the beauties of the Ampère theory without possessing the vital defect of the same-namely, the assumption of molecular currents. Without enlarging further upon the subject, I would say that I look upon all electrostatic current and magnetic phenomena as being due to electrostatic molecular forces.

The preceding remarks I have deemed necessary to a full understanding of the subject as it presents itself to my mind.

Of all these phenomena the most important to study are the current phenomena, on account of the already extensive and ever-growing use of currents for industrial purposes. It is now a century since the first practical source of current has been produced, and ever since the phenomena which accompany the flow of currents have been diligently studied, and through the untiring efforts of scientific men

Lecture delivered before the American Institute of Electrical Engineers at Columbia College, New York, May 20.

the simple laws which govern them have been discovered. But these laws were found to hold good only when the currents are of a steady character. When the currents are rapidly varying in strength, quite different phenomena, often unexpected, present themselves, and quite different laws hold good, which even now have not been determined as fully as is desirable, though through the work, principally of English scientists, enough knowledge has been gained on the subject to enable us to treat simple cases which now present themselves in daily practice.

The phenomena which are peculiar to the changing character of the currents are greatly exalted when the rate of change is increased, hence the study of these currents is considerably facilitated by the employment of properly constructed apparatus. It was with this and other objects in view that I constructed alternate-current machines capable of giving more than two million reversals of current per minute, and to this circumstance it is principally due that I am able to bring to your attention some of the results thus far reached, which I hope will prove to be a step in advance on account of their direct bearing upon one of the most important problems-namely, the production of a practical and efficient source of light.

The study of such rapidly alternating currents is very interesting. Nearly every experiment discloses something new. Many results may, of course, be predicted, but many more are unforeseen. The experimenter makes many interesting observations. For instance, we take a piece of iron and hold it against a magnet. Starting from low alternations and running up higher and higher, we feel the impulses succeed each other faster and faster, get weaker and weaker, and finally disappear. We then observe a continuous pull; the pull, of course, is not continuous; it only appears so to us; our sense of touch is imperfect.

We may next establish an arc between the electrodes and observe as the alternations rise that the note which accompanies alternating arcs gets shriller and shriller, gradually weakens, and finally ceases. The air vibrations, of course, continue, but they are too weak to be perceived; our sense of hearing fails us.

We observe the small physiological effects, the rapid heating of the iron cores and conductors, curious inductive effects, interesting condenser phenomena, and still more interesting light phenomena with a high-tension induction coil. All these experiments and observations would be of the greatest interest to the student, but their description. would lead me too far from the principal subject. Partly for this reason, and partly on account of the vastly greater importance, I will confine myself to the description of the light effects produced by these currents.

In the experiments to this end a high-tension induction coil or equivalent apparatus for converting currents of com. paratively low into currents of high tension is used.

If you will be sufficiently interested in the results I shall describe as to enter into an experimental study of this subject; if you will be convinced of the truth of the arguments I shall advance, your aim will be to produce high frequencies and high potentials-in other words, powerful electrostatic effects. You will then encounter many difficulties, which, if completely overcome, would allow us to produce truly wonderful results.

First will be met the difficulty of obtaining the required frequencies by means of mechanical apparatus, and, if they be obtained otherwise, obstacles of a different nature will present themselves. Next it will be found difficult to provide the requisite insulation without considerably increasing the size of the apparatus, for the potentials required are high, and owing to the rapidity of the alternations the insulation presents peculiar difficulties. So, for instance, when a gas is present, the discharge may work by the molecular bombardment of the gas and consequent heating, through as much as an inch of the best solid insulating material, such as glass, hard rubber, porcelain, sealing-wax, etc., in fact, through any known insulating substance. The chief requisite in the insulation of the apparatus is, therefore, the exclusion of any gaseous matter.

In general, my experience tends to show that bodies which possess the highest specific inductive capacity, such as glass, afford a rather feeble insulation to others, which, while they are good insulators, have a much smaller specific

inductive capacity, such as oils, for instance, the dielectric. losses being no doubt greater in the former. The difficulty of insulating, of course, only exists when the potentials are excessively high, for with potentials such as a few thousand volts there is no particular difficulty encountered in conveying currents from a machine giving, say, 20,000 alternations per second, to quite a distance. This number of alternations, however, is by far too small for many purposes, though quite sufficient for some practical applications. This difficulty of insulating is fortunately not a vital drawback; it affects mostly the size of the apparatus, for, when excessively high potentials would be used, the light-giving devices would be located not far from the apparatus, and often they would be quite close to it. As the air-bombardment of the insulated wire is dependent on condenser action, the loss may be reduced to a trifle by using excessively thin wires heavily insulated. Another difficulty will be encountered in the capacity and self-induction necessarily possessed by the coil. If the coil be large-that is, if it contain a great length of wireit will be generally unsuited for excessively high frequencies; if it be small, it may be well adapted for such frequencies, but the potential might then not be as high as desired. A good insulator, and preferably one possessing a small specific inductive capacity, would afford a twofold advantage. First, it would enable us to construct a very small coil capable of withstanding enormous differences of

potential; and secondly, such a small coil, by reason of its smaller capacity and self-induction, would be capable of a quicker and more vigorous vibration. The problem then of constructing a coil or induction apparatus of any kind possessing the requisite qualities I regard as one of no small importance, and it has occupied me for a considerable time.

The investigator who desires to repeat the experiments which I will describe, with an alternate-current machine, capable of supplying currents of the desired frequency, and an induction coil, will do well to take the primary coil out and mount the secondary in such a manner as to be able to look through the tube upon which the secondary is wound. He will then be able to observe the streams which pass from the primary to the insulating tube, and from their intensity he will know how far he can strain the coil. Without this precaution he is sure to injure the insulation. This arrangement permits, however, an easy exchange of the primaries, which is desirable in these experiments.

The selection of the type of machine best suited for the purpose must be left to the judgment of the experimenter. There are here illustrated three distinct types of machines, which, besides others, I have used in my experiments.

Fig. 1 represents the machine used in my experiments before this institute. The field magnet consists of a ring of wrought iron with 384 pole projections. The armature comprises a steel disc to which is fastened a thin, carefully welded rim of wrought iron. Upon the rim are wound