earnestly now than in his days, what is the ultimate reality behind the reality of the perceptions? Are they only the pebbles of the beach with which we have been playing? Does not the ocean of ultimate reality and truth lie beyond?

RECENT PROGRESS IN THE USE OF ELECTRIC MOTORS.*

BY PROF. G. FORBES, F.R.S.

In any comparatively new industry, as electrical engineering, a great deal of mental "striction" must be got over to get people to adopt new methods even when known to be an improvement.

Lord Rayleigh in his presidential address in 1884 expressed his astonishment that while no addition to our electrical knowledge of 50 years previously was required to develop the dynamo, it was so slow in being introduced. The same is true in England now, even of electrical inventions which have been proved by long and extensive experience in other countries to be economically desirable.

It is the duty of engineers who see and inspect such work abroad, to urge upon people at home the importance of their inventions, and point out the troubles which have been met and overcome elsewhere so as to avoid failure, and to point out the directions in which different inventions are being adopted, modified, or rejected, as the result of extensive practical experience. Even in electric lighting, I am sure more than one company will admit that in following this rule some of us have saved them from buying costly experience in the past. In saying this I recognise the fact that all countries look upon England as having improved the dynamo more than any other country. In the application of electric motors I have noticed three directions in which this country needs the testimony of independent and impartial people to assist the value of applications which in some other countries are generally adopted. These are (1) electric rail ways, (2) replacing shafting in shops, especially for cranes, by electric conductors and motors, (3) transmitting power to a distance from waterfalls by means of electricity.

My remarks on these heads are largely founded on experience gained in visits to the United States, and also from a very thorough investigation of the utilisation of water power in all parts of Switzerland, undertaken this summer in conjunction with Prof. Unwin.

1. Electric Railways. These are thoroughly established in America on the cheapest system-i.e., electricity supplied from a central station by overhead wires. The extensive adoption of electric tram lines in America, and the small number in England, is entirely due to the fact that they allow these overhead conductors and we do not generally do so. The electric lines in America are one-half of the horse car lines in number, and are rapidly ousting horse lines as well as steam and cable lines; and yet it is extremely difficult to get correct figures of the cost. The most trustworthy estimates seem to vary between 4.18 and 6.00 cents per car mile, including coal, attendance, land, buildings, machinery, line, oil, water, and waste. The question of repairs is serious and must be reduced. Most of the lines adopt spur gearing to reduce the speed from the electric motor to the car axles. They generally use two pinions and two spur wheels. This introduces great friction. It is very generally accepted that 8 h.p. is lost in gear friction, though this seems somewhat incredible, being about 30 per cent. These cars are large, and the motors are 30 h.p. This enormous power is absolutely demanded to enable them to start on a gradient with facility, and they do this. There is no crawling about these cars. You feel that there is plenty of power for the work. The noise on these cars used to be very considerable, and the injury to watches through magnetisation was at one time an objection. The noise from the gearing, especially when worn, has been deadened by enclosing the motor and gearing in cast-iron boxes. The magnetisation of watches is prevented by adopting a suitable type of motor. The type first advocated, I believe, by Eickmeyer in America, and myself in England, in which the magnetising coils are wound round the armature when we want the magnetism instead of round the field magnets, is now being adopted by the Thomson-Houston Company, which has done such splendid work in street railways.

Another source of trouble in motors used to be the brushes, for sparking is liable to be very violent with the variable load of a tram motor, and the commutators wear away rapidly. Since my carbon brushes have been introduced this difficulty has entirely disappeared, and the motors can be used with any variation of load, and can be reversed without wearing of the commutator and with very little sparking. Even in stationary motors they are now generally adopting these brushes, and also in dynamos.

The loss in double reducing gear and the wear and tear led to all the important companies turning to single reducing gear with rather heavier motors. It would at first appear impossible to go further, and adopt armatures on the wheel axles without sacrificing the great advantage of gearing which allows the motors to be independently supported without being subjected to the same shocks as the wheel axles. In spite of this, the Westinghouse Company has introduced a gearless motor, which has strength enough to stand the shocks. But other inventors had the idea of fixing the armature alone on the axle and supporting the field magnet wholly on springs-to support it partially on springs is of little value. Now, with ordinary motors the armature cannot have up and down motion relatively to the pole-pieces. But Mr. Short, of the Brush Company, introduced a motor with pole-pieces, Paper read before the British Association.

the sides of which allows an up and down motion without fear of the armature windings striking the pole-pieces. If the difficulty of end thrust is overcome, this ought to be an important step. But in this direction the most important and promising plan seems to be that adopted by Eickmeyer and Field. They support the whole motor in guides on springs, and connect the motor axle and the wheel axle by cranks and a coupling bar, the cranks on the right and left sides being at right angles to each other. This serves to reduce gearing friction to a minimum, while completely obviating shocks.

It may be well to give the result of American experience as to the injuries from shocks to the motor. In the first place, every manufacturer there has had to buy his own experience on one head-viz., that all loose wires such as those which join field magnet coils, or those passing from armature to commutator, are fractured by vibration. This experience has been universal, and the South London Electric Railway has also bought the same experience. The remedy lies in making such loose connections of flexible stranded wire. The other serious result of vibration is that the insulation, especially of the armature, is broken off, and short circuits occur. In America spur gearing is almost universal, but in Switzerland the Oerlikon Company are introducing worm gearing, which has been so much approved by M. Reckenzaun. Storage batteries have not generally been successful in America, but some trials have worked very well. In the last few years I have scen several of them in the States which seemed to promise well, but nothing has come of them.

The Thomson-Houston Company are now experimenting with heavy locomotives to drag trailer cars. They have not yet decided to adopt them, and in the plans proposed for rapid transit in New York I see a tendency to go in for separate motors on all the axles of a train, which is the only plan that utilises all the characteristic advantages of electric motor propulsion for long and rapid trains. We thus abolish the excessive weight of a locomotive, we are able to use lighter and less expensive rail, wear and tear of permanent way is diminished, and grinding action in going round curves. If trains are supplied by sufficient power they are not limited by rail friction to going up slight inclines, nor to getting up speed slowly, On a line with many stops the time occupied in a complete journey is thus largely reduced.

2. Replacing Shafting by Electricity.-The benefit of replacing

on cranes.

shafting by electric conductors and motors has been thoroughly appreciated in America. Everyone knows of the hundreds of motors for small work which are supplied with electricity by central stations in Boston and New York besides other places, and of the large number of electric lifts supplied by the Otis Company, with the electric motors designed by Eickmeyer. I will only place before English manufacturers two of the establishments where a statement of what has been done is enough to bring conviction to the mind of every shrewd and sensible employer of power. In the great works of William Sellars and Co., shafting has been abolished as far as possible. I saw seven motors at work, chiefly I saw a 15-h.p. Sprague motor working a 30-ton travelling crane, which has been in continuous use for the last two years. They, of course, use carbon brushes, and the motor has never given any trouble. Ordinarily working at 200 volts and 60 amperes, the latter have been increased to 110 for a short time without injury. There are also electric connections all over the shop, by means of which motors can be used at any time. The second establishment is Baldwin's locomotive factory, where 16 to 20 locomotives are sent off every week, and where space is 90 valuable that there is no room for shunt lines, and where a 100-ton travelling crane picks up one out of these 20 and puts it down where wanted. This fine travelling crane and every other crane in this huge part of the works are driven by electric motors.

3. Transmitting Power to a Distance. With regard to transmission of power to a distance from waterfalls, I have seen little to chronicle in America, and what there is seems rather antiquated, but in Switzerland important work has been done by continuous and alternating currents. The high-tension electrical work in connection with continuous currents that most impressed me was what has been done by Cuenod, Sautter, and Co., Geneva. Their six-pole machines, with Gramme commutators, up to 2,000 volts, designed by M. Thury, seem to work admirably and sparklessly, and I must here state my conviction, which I did not previously have, that the insulation of such a machine can be made perfect, as there done, by supporting the dynamo or motor on a number of alternate slabs of vulcanised rubber and porcelain, and by connecting the shafts by Raffard couplings. This consists of a disc in the end of each of the two shafts to be coupled, which are as nearly in line as possible. Each disc has half-a-dozen steel pins on a circle near its periphery. In one of the discs the circle of pins is, say, lft. diameter, and in the other Ift. 6in., and the two circles of pis are in the same place and are connected in pairs by indiarubber rings.

This avoids the necessity of perfect alignment and ensures perfect insulation At Oyonnax, a small village with artisans who make combs and wooden pipes and other articles, the lathes are driven by electric motors from a low-pressure supply. To get this power, a waterfall six miles distant is used. Each turbine, of 120 h.p., drives a dynamo of 1,800 volts, which is sent by overhead conductors to Oyonnax, where it drives a 1,800-volt motor, which drives a low-tension dynamo which supplies three three-wire circuits-one for power, one for public light, and one for private light. They have supplied similar plant in many other places.

I will not take up time with describing different works of this kind, but I will now say something about the use of multiphase or rotary currents, about the prospective use of which so much has been published. I have seen the machines and transformers in course of construction at Oerlikon, and the insulators which

have been used, and the mechanical design is excellent. This plant is now about to be tried at Frankfort over a distance of 112 miles. Tests will be made, and we shall soon know something definite about their working. I have not seen the Dobrowolski machines, but both these and the others have been described in the technical journals. The principle employed by Mr. Brown, of Oerlikon, is the fact, discovered by Wilde, that an alternating dynamo used as a generator will drive a second similar machine as a motor; but three separate circuits are put on the armatures, SO that three separate currents travel along the line and reach the electric motor in succession, so that there is alway one circuit at least on the armature of the motor, tending to drive it round. Now these three currents in the line will interfere seriously with each other-just as it was found at New Orleans, that two circuits in unusual proximity for 1 miles, and fed by two separate alternators, interfered with each other so much that the lamps on both circuits flickered badly. I find that, in order to prevent this, it is necessary that along the whole line the three conductors shall be at the corners of an equilateral triangle. I can quite understand the difficulties of regulation of three currents referred to by Dobrowolski, but I think there are further points upon which information is much wanted. I want to know-for hitherto I have entirely failed to see-the advantages of this three-phase synchronising alternator over the simple alternators which do such excellent work. I have been told that Mr. Brown's machine has 96 per cent. of efficiency as a dynamo. Well, I reply that an ordinary alternator without iron, not having the hysteresis of Mr. Brown's machine, ought to have a higher efficiency. In the next place, I am told by Mr. Brown that while you cannot switch one of these three-phase synchronising motors with its load on to an electric circuit and expect it to get up to the synchronising speed, yet it will do so along with the electric generator of electricity if the latter be also started from rest. In this it certainly has the advantage over the synchronising alternator with iron, but none whatever over those without iron, which will act in precisely the same way unless the motor happens to be stopped on dead centres-i.e., with the centres of coils (in a Mordey alternator, for example) halfway between poles of the field magnets.

If this is the only gain over single-phase alternators with selfinduction, and if there be no advantage gained over alternators without large self-induction, I fail to see the merit of the complication of three phases. I would not have drawn attention to the absence of advantage, but would have preferred to await the experiments before expressing an opinion, were it not for the great attention directed to the scheme by the Press, altogether out of proportion to the results which Mr. Brown and the Oerlikon managers hope to obtain. The great experiment about to be tried at Frankfort, which interests electricians all over the world, is not to prove that transformation is efficient, but to prove that 30,000 volte can be carred along 112 miles of overhead conductor. The Dobrowolski motor does not resemble the synchronising motor, but is a modification of the Tesla motor, except that the number of currents of differing phase is increased. Here also I fail to see any cause of better work, but I await any trials that may be made with interest, and I speak as one who has worked with and made tests with the developed type of Tesla motor at Pittsburg. Mr. Dobrolwolski, however, says that whatever load may be put on this motor there is no serious difference in phase between the potential difference applied to the motor (and there is no appreciable lag) and the current. If this be so, it would be a decided improvement, but I shall require strong proof before I accept the multiphase motor as a great advance over the Tesla machine. The only advantage which it possesses over synchronising alternators without iron in the armature, and with large momentum, lies in its power to start with load on. But I do not see that in large applications this advantage is to be compared with what it loses by its want of synchronism. All shops ought to be driven at a steady speed, but in some trades, such as weaving with sensitive looms, it is essential, and even the best turbines driven at nearly constant fall, if not governed, cause the breaking of threads in a loom to be a serious drawback. On the whole I would prefer the synchronising type. But Mr. Dobrowolski claims that these machines have the further advantage over the synchronisers that they will not stop when overloaded. Now this prevalent prejudice requires examination. For my own part, after having tested Mr. Mordey's synchronising alternators on many occasions, and after having very much overloaded them, I have a strong conviction, almost amounting to a feeling of certainty, that it is impossible to put them out of step in ordinary conditions by merely increasing the load. The more you increase the load, the more current goes through them to keep them in step. They would rather get red hot than get out of step. They behave just as a continuous-current motor, or a Tesla motor, or a Dobrowolski motor behave under the same conditions. It gets hots, but it does not stop. At this stage I must say that it is much to be deplored that no conclusive experiments by any independent authority have as yet been made on the Mordey alternator as to its efficiency when used as a motor.

In concluding my remarks about the Frankfort experiment, I wish to express the admiration that electricians feel for the men who have undertaken to prove that 30,000 volts can be practically transmitted overhead for 112 miles; and for the engineers who have so ably designed such excellent mechanical machines to do the work.

I now have a word to say on the alternating synchronising motor, which it seems so difficult to get people to believe in. I have for some time past been working at its theory. I will not go into the mathematics of it now. I will content myself with stating the conclusions, and replacing analytical or geometrical proofs by a

mechanical analogy. People seem to be strangely at a loss to explain why it is that some alternators work well as motors while others do not. It has been shown that self-induction will assist this action. So many people have rushed to the conclusion that self-induction is the cause, and many a machine has been thrown away that was built on these lines. Mordey overthrew these views by showing that his machine, having less self-induction than most alternators, synchronised the best. Then, when we compare the Siemens or Ferranti alternator with the Mordey one, we see that they are electrically identical, especially as to self-induction. Why, then, does the Mordey work so well as a motor and not the Ferranti? The explanation is simply that the former has a large momentum and the other has not. I announced this explanation of the difficulty at a meeting of electricians in Paris last February, and found that M. Hospitalier had arrived at exactly the same conclusion and quite independently. I feel confident in predicting that the Ferranti dynamo, if supplied with a heavy enough flywheel, will be found to work as well as the Mordey machine as a motor. The reason of this is that the motor has dead centres to get over, just like a steam engine During the alternations the current is reduced to zero twice during each complete period, so also is the back E.M.F. of the motor, and at each of these points we have dead centres beyond which the motor cannot move except by fly. wheel action. During a considerable part of the complete period the motor has higher E. M. F. than the generator, and is consequently retarded. There is another point-viz., that the rotation of such a machine is not perfectly uniform. It is 1etarded when doing work, and accelerated when work is being done upon it, and the less the momentum the greater is the variation of speed. I will not go further into the theory, which I propose to give fully elsewhere, but the consideration of these views will be made clearer by a mechanical illustration.

Imagine two wheels on independent axles connected by a coupler which is not rigid, but consists of a piston attached to one of the wheels and a cylinder attached to the other; the piston working in the cylinder. If one of these is driven and slowly increased in speed, the other will rotate with it, but if it be loaded with a brake it cannot get over the dead centres unless it has momentum. Here the air friction, varying as the relative velocity of piston and cylinder, is the force which moves the motor wheel, and this corresponds to the electric current conveyed in the electric motor analogy. It is supposed that the wheels are so distant_that_the coupler is always parallel to the line of centre. The E.M.F. of either machine is represented by the inclination of the line of the coupler to tangent of the wheel at its point of attachment.

In the electrical problem, if 0 and 01 are the phases of generator and motor, and if v and v are their velocities at the moment, and if M and M1 are the strengths of field, then, omitting self-induction altogether, their E. M.F.'s are proportional to

tion of electric energy through that class of conductors known as electrolytes.

The propagation of electric energy along metallic conductors is invariably found to produce the following four phenomena:

I The electric energy is propagated with the velocity of light. II. An electromagnet field is produced.

III. Induced currents are produced in neighbouring conductors. IV. Heat is produced in the conductor uniformly along its length proportional to the strength of the current and the resistance of the conductor.

These four phenomena are also produced during electrolysis. They are, however, accompanied by a fifth phenomenon-namely, chemical decomposition at the electrodes, and this chemical decomposition is strictly proportional to the strength of the current, but not to its intensity.

Hence, by infinitely increasing the potential and diminishing the strength of the current, we can make the absorption of electrical energy due to chemical action as small as we please; and thus we can establish so complete an analogy between the propagation of electric energy along metallic conductors and along electrolytes that any views brought forward to explain the phenomena in the one case must perforce apply to the other.

The theory of the propagation of electric energy along metals has been thus concisely defined by Prof. J. J. Thomson:

"The velocity of transmission of an electric impulse along a wire is, according to Maxwell's theory, equal to the velocity with which light passes through the dielectric in which the energy resides, and the function of the wire seems merely to be that of guiding the discharge which travels at a rate fixed by the dielectric."

Prof. H. Hertz has recently shown that when an electric oscillation travels along a wire the electric force produces a mechanical effect at right angles to the wire, whilst the magnetic force which accompanies it tends to repel a ring brought into its vicinity; thus there are two vibrations perpendicular to each other, the nodes of the one coinciding with the antinodes of the other, passing along the wires, whence he concludes that "from the above experiments with conductors of very simple form it is evident that a conductor of any form, when placed in the path of electromagnetic wires, is subject to forces of a very complex character."

Since a guiding conductor surrounded by dielectric is required (according to the above theory) for the propagation of electric energy in definite directions, the question arises, "How can an electrolyte act as such a guiding conductor?"

For this there are two possible explanations. Either (I.) the bulk of the electrolyte might be considered the conductor, and the surrounding medium the dielectric, such as glass or air, or (II.) in the electrolyte itself a rearrangement of molecules is produced, some (i.e., the best conducting) forming the guiding conductors along the lines of force between the electrodes, other dielectric tubes surrounding the same.

The first proposition is untenable, for although it explains how an electromagnetic field may be produced outside the electrolyte, it utterly fails to explain how a fairly uniform field is produced inside it.

Molecular chains have formed the basis of every theory of electrolysis since they were first proposed by Grotthus, although the mode of action of the molecules has been explained in a great number of different ways.

The molecular arrangement required for the second proposition i.e., molecular chains surrounded by dielectric tubes-was first proposed by Prof. G. Wiedemann, who brings weighty proofs in its favour, but who also, like his predecessors, assumes that the current passes through the lecular chain. He has, however, provided the requisite mechanism for the application of Clerk Maxwell's theory to electrolysis.

The electric energy in being propagated through these dielectric tubes along the chain of conducting molecules produces these magnetic and electric effects, which act chemically on the dielectric, decomposing the molecules into atoms or weakening their affinity along the zones of intense electric action surrounding each molecular chain. A similar view was already suggested by Faraday, when he considers the electric current to be "an axis of power having contrary forces exactly equal in amount in opposite directions," modifying the chemical affinity of the electrolyte in directions parallel to the axis, and providing the conditions for the transfer of electro-positive and negative ions in their respective directions.

That there is a tendency for a strong electric field to produce molecular decomposition is evident from the action of the silent discharge and the electric, and also from such observations as those made by Bouty of electrolytic action on the surface of condenser plates.

The view proposed, which considers metallic and electrolytic conduction as identical, finds strong support in the following investigations.

Prof. J. J. Thomson finds, as the result of experiments, "that the velocity of propagation of a rapidly alternating current along an electrolyte surrounded by air cannot differ much from the rate along a wire"; and in examining the resistance of electrolytic alternating currents, "The results obtained agree sufficiently well to enable us to say that the relative resistance of electrolytes is the same when a current is alternating a hundred million times a second as for a steady current."

Prof. Mengarini, of Rome, in a very exhaustive paper on electrolysis by alternating currents, formulates the following law: "4. A limiting value to the rapidity of alternations exists, beyond which decomposition does not take place," which he proves both theoretically and experimentally; and he finds that at the limit "the

voltameter only becomes heated by the passage of the current like an ordinary metallic conductor. He also states in his conclusions: "6. A voltameter traversed by an alternating current behaves like a metallic conductor possessing self-induction.

A committee appointed by the British Association has also investigated a series of solid compounds-such as sulphides and selenides some of which conduct purely metallicly, others purely electrolytically, and others in both ways at the same time, and declared themselves unable to draw any marked line of distinction between these bodies.

To resume. The number of the molecular chains formed will depend on the strength of the electric field and on the concentration of the electrolyte, whilst the cross-sectional area of each zone of decomposition will depend on the strength of the current and number of chains, and the current density will be measured by the number of such chains in the cross-section of the electrolyte.

The existence of these zones explains

I. How the atoms can travel along molecular chains towards their respective electrodes without recombination.

II. Why the atoms are given off as molecules at the electrodes only, because there the electric field, being weakest, and atoms of one kind preponderating, they combine and are given off.

By artificially weakening the electric field by introducing a metallic plate into the path of the molecular chains, such plate acts similar to an electrode. Mr. A. Tribe, by interposing silver plates in a copper sulphate cell, obtained one end coated with copper, the other with protoxide of silver, and found the boundary line of the zone of deposition to be at right angles to the line of flow of the current. This enabled him to observe the refraction of this line of flow by interposing a porous vessel with water, whose parallel sides were inclined at an angle of 45deg. to the sides of the rectangular electrolytic trough, a most important verification of the directive tendency of the current in an electrolyte.

Prof. J. J. Thomson has also shown that an electric field is weakened in the presence of a solid dielectric, because the surface tension is increased. Hence, if a solid dielectric is intruded into a zone of intense electric action, by sending the current through a porous diaphragm or a cracked glass plate, the fields will be weakened and atoms liberated, as abundantly proved by the experiments of Grotthus, F. Braun, Ostwald, Tamman, Overbeck, and others.

III. Why the atoms cannot escape through out of the liquid is explained by the directive force preventing the atoms escaping laterally out of the decomposing zones.

It is obvious that only an exceedingly small E.M.F. would be required to produce the minimum zone of decomposition necessary for electrolysis along a single or few molecular chains, and, since a weak electric field could only have a few lines of force, there would only be a few such rows, and this gives us an expla nation for the electrolysis produced by the infinitesimal currents observed by Helmholtz, M. Deprez, and others.

Also, if two bad conductors of slightly varying conductivity be mixed-such as alcohol and water-the conditions are provided for electrolytic action, the better conducting forming the guiding conductors, the other dielectric tubes, whence a greatly increased conducting power is produced and observed; as witness the experi ments of Gladstone and Tribe, Overbeck, Pouillet, Ayrton and Perry, and others.

This also explains the action of exceedingly minute quantities of impurities on influencing the conductivity of electrolytes. The assumption that the solvent is primarily decomposed suffices to explain all the chemical phenomena observed in electrolytic cells, and was fully accepted by the older electricians, being specially worked out by Berzelius and his school.

The electrolysis of solutions by strong currents gives strong support to this view, for when constituents of the solvents are more rapidly generated than they can be absorbed by secondary chemical action they are given off in the free state. I have shown this to be the case for copper sulphate solutions, from which I have obtained oxygen and hydrogen by sufficiently increasing the strength of the current. Kohlrausch also states that in very dilute solutions water is decomposed.

The complicated phenomena classed under polarisation are mainly due to voltaic currents arising from chemical changes taking place at the electrodes and their physical effects.

The phenomenon known as wandering of the ions has been shown by Profs. Wiedemann and Quincke to be due to three

as electrical endosmose.

It is obvious that these explanations may also be adopted in connection with the above expressed views.

In order to corroborate the theory of molecular chains, I have carried out a series of experiments with different apparatus to study whether the displacement of the molecular conductors would influence the conductivity. I found that the resistance of a jet of electrolyte, which was caused to flow at varying speeds between the electrodes, rose proportional to the velocity of the electrolyte up to a maximum of about 10 per cent. of the total deflection. In order to ensure the result being solely due to the velocity of the jet and not to diminution of the area of the conductor, the electrodes, carefully insulated except at the places where the jets, one to each electrode, impinged, were kept immersed in separate cells

Faraday has shown that an interrupted current flowing through an electromagnet is able to induce a current in a secondary coil made of an indiarubber tube filled with an electrolyte wound round the keeper.

Considering it to be of interest to have both a primary and secondary coil of electrolytic conductor, I constructed two flat spirals of indiarubber tubing filled with acidulated copper sulphate, and provided with copper electrodes; for the primary a continuous current of 90 volts was employed, which was simply interrupted by means of an electric bell worked from an independent

battery.

The secondary coil was connected with a Sir Wm. Thomson 60ohm reflecting galvanometer; a thermo current giving 10 divisions was observed, but the effect of the induced alternating current was to produce intermittently deflections of over 50 divisions on each side of the zero, thus removing all doubt of the success of the experiment.

The complete analogy between an electrolyte and a highresistance wire led me to suspect that if such a wire were inserted between the electrodes, electrolysis would be observed at the ends. On referring to the literature I found that Jacobi had obtained the desired result with a German silver wire in a copper sulphate solution, but did not obtain the result with platinum. Having some thin platinoid wire at hand I determined to repeat the experiment, coiling the wire to increase its resistance. Copper was deposited along about one half of it, beginning slowly at the negative electrode whilst the other half turned black by oxidation, and was gradually destroyed at the end nearest the positive electrode.

I know that the view I have ventured to bring before you leaves many facts connected with electrolysis as yet unexplained, but the same must be admitted for all other theories on the subject hitherto propounded, over which it has, I believe, the advantage that it brings the propagation of electric energy along electrolytes into harmony with the now generally accepted theory of Clerk Maxwell of its propagation along metallic conductors, and that it offers an explanation of the electrical as well of the chemical phenomena observed.

dt

Q=d&_d4 dy

where dG/dt stands for the total time-rate of change of G, the component of vector potential in the direction of y, and & denotes partial differentiation. Also since H, the component along z, does not perceptibly vary along x, if the direction of propagation be as taken here along z-8 G/dz, denotes magnetic induction through unit of area in the plane of y z. Hence any part of the total timerate of variation of - 8 G/8 z will denote the space-rate of variation, and space differentiations of the part are commutative. This is to in the direction of %, of an E. M.F. parallel to y, provided the time

be borne in mind in what follows.

Now, if the displacement of the ether particles from the undisturbed positions be taken as parallel and proportional to the electric displacement, and C be the component of magnetisation of the substance in the direction of z due to the existence of the molecular magnets, then, considering the electric displacement ƒ in the direction of x, the component magnetic force in the direction of a will be, approximately, e C8 f/8, and thus the magnetic induction through unit of area in the plane of yz is μe Cdfð =, where e is a coefficient of proportionality. The time-rate of variation of this is

where & denote component displacements of a portion of ether in two rectangular directions, perpendicular to that of %, taken as the direction of propagation.

It is suggested by the gyrostatic investigation that it ought to be possible to explain the magneto-optic rotation on the electromagnetic theory of light, as a consequence of the existence of the similarly oriented small magnets which are supposed embedded in the medium with their axes in the direction of propagation of the ray, and therefore producing the magnetisation of the medium in that direction. Such a theory, while analogous to the gyrostatic theory, would be quite independent of the latter.

In consequence of the motions of the ether, the directions of the chains of magnetised molecules, which are supposed to exist along the direction of magnetisation (here taken as axis of %), in the undisturbed state of the medium, are continually undergoing change at every point, and thus the direction of the axial magnetic force along each chain also undergoes alteration. It is obvious that if the displacements be everywhere small the actual magnitude of this force will sustain only a very small percentage of alteration, but that each such small change of direction will produce a component magnetic force in each of the two directions at right angles to the axis. The calling into existence of these components will produce corresponding E. M. F.'s tending to increase or diminish the electric displacement.

Abstract of a paper read before the British Association.

Q=

8 G δι

e C 82 F 84 4π δε бу

&Q δι

=

82 G eC 83 F

812 4π διδα

But the displacement current in the direction of y is dg/dt, and this is K/4. 8Q/St. Also by the equations of currents & got 1/4 μ d2 G/ôz22. Therefore we have the equation

1

=

=

Απμ

K & Q 4π δι δι

These two equations are identical in form with those quoted above, as given by the gyrostatic theory, and, of course, lead to the same results; that is to say, the plane of polarisation of an electromagnetic beam would show a turning effect in a magnetised medium.

The theoretical view given above has been suggested by a reference in M. Poincaré's "Théories de Maxwell," to a note by M. Potier, in his French translation of "Maxwell's Electricity,' which appears to contain a similar theory leading to equations of the same form. I have not seen M. Potier's note, and it is possible that it has completely anticipated the present paper.

The fundamental assumption here made, that f, g, h are proportional to the ether displacements scems a reasonable one, and is in accordance with the view generally held (but not yet, so far as I know, proved) with respect to the electromagnetic propagation of light. If the theory given above be otherwise satisfactory, it seems to give, by accounting for the magneto-optic effect, some support to this view. It will be observed that theory, while independent of the gyrostatic one, is analogous to the latter, the transverse E. M. F.'s in the electromagnetic theory corresponding precisely to the gyrostatic reactions in the dynamical one.

REPORT OF THE COMMITTEE ON ELECTRICAL

STANDARDS.*

Report of the committee consisting of Prof. G. Carey-Foster, Sir William Thomson, Prof. Ayrton, Prof. J. Perry, Prof. W. G. Adams, Lord Rayleigh, Dr. O. J. Lodge, Dr. John Hopkinson, Dr. A. Muirhead, Mr. W. H. Preece, Mr. Herbert Taylor, Prof. Everett, Prof. Schuster, Dr. J. A. Fleming, Prof. G. F. FitzGerald, Mr. R. T. Glazebrook (secretary), Prof. Chrystal, Mr. H. Tomlinson, Prof. W. Garnett, Prof. J. J. Thomson, Mr. W. N. Shaw, Mr. J. T. Bottomley, and Mr. T. Gray, appointed for the purpose of constructing and issuing practical standards for use in electrical

Among these the coil B.A. No. 38-77 has a special interest. It is an original platinum-silver coil which formerly belonged to Prof. Balfour Stewart, and is now in the possession of Prof. Schuster, at the Owens College. According to the label on it, it was right at 16deg. 5. According to my observations, its value is one mean B.A. unit at 14-9. This coil, therefore, would appear to have risen in value since about 1867 by 0006 B.A. U., and this result is not in accordance with the conclusions deduced in 1878 from the observations on the other platinum-silver coils then examined.

Some further experiments have been made with satisfactory results on the air condensers of the association. A megohm resistance-box has been purchased for use in comparisons of capacity. With a view to testing the permanence of the resistance standards, it was thought desirable to compare them again with the mercury standards. This was done in December and January by the secretary. The coil that was compared with two mercury tubes constructed in 1884 by M. J. R. Benoit, which had been filled at Cambridge early in the year 1885 and had remained full since. An account of the comparison was read before the Physical Society, May 9, 1891, and appears in the Phil. Mag. for July, 1891. The coils were compared with the B. A. standards, if we take, as was done in 1885, for the resistance in B. A. units of a column of mercury 100 cm. long, 1deg. in section, the value '95412 B A.U. We have the following results for the resistance of the tubes in legal ohms:

No.

37

Value in 1885 found by R T b. 99990 99917

Value in 1891

found by R T b. 99986 99913

39 The differences are only 00004 legal ohm, which is too small to feel really certain of. If we accept for the resistance of mercury the value 95352, which (B.A. Report, 1890) appears the best value, then we have

Value found by

RTb in 1891. 1 00033 ⚫99959

These comparisons were made with Ha1, and lead to the conclusion that it has remained unchanged. In November, 1890, the association was invited by the President of the Board of Trade to nominate two members to represent the association on a committee "on standards for the measurement of electricity for use in trade." A meeting of the Electrical Standards Committee was held on December 2nd, and it was agreed to suggest to the council of the association the names of Prof. Carey-Foster and Mr. R. T. Glazebrook as representatives. These gentlemen were appointed by the Board of Trade, together with Mr. Courtenay Boyle, C.B., Major Cardew, Mr. E. Graves, Mr. W. H. Preece, Sir William Thomson, Lord Rayleigh, Dr. John Hopkinson, and Prof. Ayrton. This committee, after various meetings, drew up a report, a copy of which is printed as Appendix I. to this report. The standards of resistance, constructed in accordance with Resolution 6 of the * Report presented to the British Association.

report, are now in the hands of the secretary, and are being compared with the standards of the association. Numerous experiments on the methods of constructing Clark's cells and on the absolute E. M. F. of such cells have been made at the Cavendish Laboratory by Mr. Wilberforce, Mr. Skinner, and the secretary. These are still incomplete, but the experiments, so far as they have been finished, lead to the value 1·434 volts at 15deg. for the Ě.M.F. of the cell. The value found by Lord Rayleigh was 1435 at the same temperature.

Mr. Fitzpatrick has continued his experiments on the resistance of silver. An account of these will be found in Appendix II. The committee ask for reappointment, with omission of the names of Principal Garnett and Mr. H. Tomlinson, and addition of those of Dr. G. Johnstone Stoney and Prof. S. P. Thompson. They recommend that Prof. Carey-Foster be chairman, and Mr. R. T. Glazebrook secretary. They further ask to be allowed to retain an unexpended balance of last year's grant, amounting to £17. 48. 6d., as well as for a new grant of £10.

APPENDIX I.

Report of the Electrical Standards Committee appointed by the Board of Trade to the Right Hon. Sir Michael Hicks-Beach, Bart., M. P., President of the Board of Trade.

In compliance with the instructions contained in your minute of the 16th December last, that we should consider and report whether any, and if so what, action should be taken by the Board of Trade under Section 6 of the Weights and Measures Act, 1889, with a view to causing new denominations of standards for the measurement of electricity for use for trade to be made and duly verified, we have the honour to submit the following report: 1. Before coming to a decision as to the points referred to us, we were anxious to obtain evidence as to the wishes and views of those practically interested in the question, as well as of local authorities who are concerned in the administration of Weights and Measure Acts. 2. With this view we prepared draft resolutions embodying the proposals which, subject to further considerations, appeared to us desirable, and forwarded copies to the represen tatives of various interests for criticism. Copies were also for warded to the Press. We also invited the following bodies to nominate witnesses to give evidence before us: the Association of Chambers of Commerce of the United Kingdom, the Association of Municipal Corporations, the London County Council, and the London Chamber of Commerce. 3. In response to this invitation the following gentlemen attended and gave evidence: on behalf of the Association of Chambers of Commerce, Mr. Thos. Parker and Mr. Hugh Erat Harrison; on behalf of the London Council, Prof. Silvanus Thompson; on behalf of the London Chamber of Commerce, Mr. R. E. Crompton. The Association of Municipal Cor porations did not consider it necessary to offer any oral evidence, but the following resolution passed by the Law Committee of that body was adopted by the council of the association: "The committee are of opinion that, assuming that the science of electricity has advanced 80 far that it is now possible properly to define the three units referred to in the Board of Trade letter-i.e., the ohm, ampere, and voltand to construct an instrument for the purpose of standard measurement, the time has arrived for the Board of Trade to take action thereon." 4. In addition to the witnesses above referred to, the following gentlemen were invited to give evidence, and we are indebted to them for valuable information and assistance: Dr. J. A. Fleming, and Dr. Alexander Muirhead. 5. We also had the advantage of the experience and advice of Mr. H. J. Chaney, superintendent of weights and measures, who, at the request of our chairman, was present at our meetings. 6. After a careful consideration of the questions submitted to us, and the evidence given by the various witnesses, we have agreed to the following

resolutions:

"1. That it is desirable that new denominations of standards for the measurement of electricity should be made and approved by her Majesty in Council as Board of Trade standards. 2. That the magnitudes of these standards should be determined on the electromagnetic system of measurement with reference to the centimetre as unit of length, the gramme as unit of mass, and the second as unit of time, and that by the terms centimetre and gramme are meant the standards of those denominations deposited with the Board of Trade. 3. That the standard of electrical resistance should be denominated the ohm, and should have the value 1,000,000,000 in terms of the centimetre and second. 4. That the resistance offered to an unvarying electric current by a column of mercury of a constant cross-sectional area of one square milli metre, and of a length of 106.3 centimetres at the temperature of melting ice, may be adopted as one ohm. 5. That the value of the standard of resistance constructed by a committee of the British Association for the Advancement of Science in the years 1863 and 1864, and known as the British Association unit, may be taken as '9866 of the ohm. 6. That a material standard, constructed in solid metal, and verified by comparison with the British Association unit, should be adopted as the standard ohm. 7. That for the purpose of replacing the standard, if lost, destroyed, or damaged, and for ordinary use, a limited number of copies should be constructed, which should be periodically compared with the standard ohm

and with the British Association unit.

S. That resistances

constructed in solid metal should be adopted as Board of Trade standards for multiples and sub-multiples of the ohm. 9. That the standard of electrical current should be denominated the ampere, and should have the value one-tenth (0·1) in terms of the centimetre, gramme, and second. 10. That an a solution of unvarying current which when passed through nitrate of silver in water, in accordance with the specification attached to this report, deposits silver at the rate of 0.001118 of a