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"1. At what price you will be prepared to supply energy for public lamps, and the mode in which the charge will be ascertained.

"2. To what class of lamps for street lighting is your system applicable.

"3. The quarterly charge to be made to private consumers for electricity supplied per Board of Trade unit, stating clearly how such charge will be arrived at in proportion to the number of hours' consumption in each case of the maximum supply applied for by each consumer, adding the cost of rent of meter quarterly."

The Vestry Clerk also added that preference might probably be accorded to such company as, other advantages being equal, would confine its operations within the limits of Paddington, so as to facilitate at any future period the purchase of the works by the local authority.

In reply to these questions, answers were reported by the committee as having been received from Mr. Sydney Morse; the Westminster Electric Supply Corporation, Limited; the House-to-House Electric Light Supply Company, Limited; the Electricity Supply Corporation, Limited; and the Kensington and Knightsbridge Electric Lighting Company, Limited.

Mr. Morse, in his letter, wrote:

"1. My clients will either be prepared to supply energy to public lamps at 8d. a unit or by special agreement, but I must point out that until the question whether my clients are to treat on the basis of an order for the whole of the parish or for part only has been determined, it is impossible to give a more definite answer as to what agreement might be arranged with you.

"2. The system to be adopted is applicable to all classes of lamps, both arc and incandescent.

"3. In reply to 3, my clients will propose to charge in accordance with the amount of electricity supplied, as certified by a proper meter (rented at, say, 5s. a quarter).

"The quarterly minimum charge would probably be 25s., but, if the minimum is meant by the question, to be in proportion to the maximum, my clients consider that if the maximum required per quarter is 100 units, the minimum should be 40, and so on in proportion."

Mr. Frank Iago (the secretary of the Westminster Electric Supply Association, Limited) replied:

"1. We are prepared to supply energy for public lamps at sixpence per unit.

"The charge could be estimated by measuring the exact quantity of energy supplied by meter, or by a calculation based on the amount of current required to burn the carbons at any specified candle-power your vestry may desire the lamp to give, and the number of hours the lamps would be in operation. A monthly, quarterly, or yearly rate would be quoted when our Board are in possession of your requirements. It is suggested that it would be desirable for your vestry to appoint a committee to inspect our lamps for street lighting before coming to any decision.

"2. The company will undertake to supply current adaptable for any class of lamp your vestry may decide upon.

"3. The company are prepared to charge private consumers, either at a fixed charge per light, to be hereafter agreed upon, or by meter at 8d. per unit, charging to an ordinary consumer for meter rent, 5s. per quarter.

"The company are prepared to erect works in Paddington, and to keep separate accounts so as to facilitate at a future date the purchase of the works by the local authority."

On behalf of the House-to-House Electric Light Supply Company, Limited, Mr. H. St. John Winckworth wrote as under :

"1. The price at which we shall be prepared to supply energy for public lamps would be in accordance with the provisions of the provisional order granted to us by the Board of Trade, which has been fixed for the whole of London at the rate of 8d. per Board of Trade of electricity supplied. Although we should be

[SEPTEMBER 20, 1889.

quite willing to reduce this price very considerably, owing to the long number of hours the public lamps are burning, we are afraid that clause 20 of the Electric Lighting Act, 1882, prohibits us from so doing. The enclosed scale of charges, which we are at present adopting at Kensington, and is in use at Eastbourne, would work out equal to about 44d. per Board of Trade unit for public lighting. The mode in which the charge for electricity will be ascertained, is by the use of an accurate meter.

"2. The system this company has adopted at Kensington is applicable to either arc or incandescent lamps.

"The quarterly charge to consumers would, we presume, be at the rate of 8d. per Board of Trade unit, in accordance with the provisions of the model provisional order issued by the Board of Trade, irrespective of the number of hours' consumption, and the maximum supply demanded.

"Our charge for rent of meter, instruments, &c., is 3d. per light per quarter. This company would be quite willing to establish a special electric lighting station for the parish of Paddington, in order to facilitate at any future period the purchase of the works by the local authority. As, however, the Board of Trade have granted to this company a provisional order to light the northern portion of Kensington, adjoining the parish of Paddington, we should probably prefer to place our electric lighting station within this parish, in order to obviate any nuisance which might be caused to the residents of Paddington, by the establishment of a central station within the district."

The reply of the Electricity Supply Corporation, Limited, was :—

"1. Energy for public lamps, if within the area of private supply, will be supplyed at 25 per cent. at least under the rate charged to the public, subject, however, to this condition :-that the price shall not be an undue preference within the Electric Lighting Act of 1882.

"2. The E.P.S. system is suitable for all classes of public lighting, whether by arc, high candle-power, glow, or ordinary incandescent lamps.

"3. The minimum quarterly charge for electricity will be 13s. 4d., and the maximum price per Board of Trade unit will be 8d. The amount will be arrived at by certified electricity meters, added to a rental of about 3s. per quarter per 100-light meter.

"4. The whole of the works to be executed under the Paddington provisional order, will be erected in the parish of Paddington, and we are willing to conform to all reasonable demands of the vestry."

Mr. R. S. ERSKINE, the secretary of the Kensington and Knightsbridge Electric Lighting Company, Limited, replied to this effect:

66

1. At 10 per cent. discount off the price we charge to private consumers under our present licence, which is 8d. per Board of Trade unit of 1,000 watts per hour.

"2. Either to large incandescent or to arc lamps. The former may be of any candle-power up to 200. The latter, from 500 candle-power upwards, as may be asked for.

"3. We do not make a quarterly charge, except in the sense that we send quarterly accounts for the quantity of electricity used, measured by meters fixed in the consumers' premises.

"Our meter rent varies from 5s. a quarter upwards5s. a quarter, meter suitable for 36 10-C.P. lamps. 68. 75 10-C.P. lamps. 108. 150 10-C.P. lamps.

99

"4. In case this company succeeds in obtaining powers to light Paddington parish, it would be prepared to put down a separate generating station and complete system for the parish, which might be worked in combination with the existing Kensington and Knightsbridge stations, or not, as may be hereafter desired."

In addition to the reply to the questions asked on behalf of the vestry, the letter of Mr. Winckworth contained a long and interesting enclosure as to the terms of supplying electricity to private consumers. Particu lars being given of the supply and cost of light, of

SEPTEMBER 20, 1889.]

"It is admitted on all hands that our houses are not at present satisfactorily lighted. The excessive heat of our rooms at night is a subject of universal complaint, and the injury to health and eyesight, and the damage to books, pictures, decorations, &c., by ordinary illuminants, is a formidable objection to their use.

"It can unhesitatingly be claimed that by the use of he electric light, supplied from central stations, the whole of the disadvantages connected with lighting by other means can be done away with. It may, indeed, be justly considered a perfect light, since it will stand he test of purity, cleanliness, coolness, convenience, teadiness, beauty, and safety.

"Purity, Cleanliness, and Coolness.-The greater or esser brilliancy of the light from other illuminants lepends upon the greater or lesser amount of oxygen which is the one ingredient in the atmosphere necessary to sustain life) which they abstract from the air. In the production of light by their use, oxygen is used p (a) in combination with hydrogen in the burning dame, and (b) in combination with carbon, the particles of which, when raised to incandescence, give out the Light.

66

The result of the first-mentioned chemical action (a) s the formation of vapour, which, being dispersed through the rooms, is condensed in the form of water, and deposited on the walls, ceiling, carpets, furniture, books, pictures, &c. The result of the second chemical action (b) is the formation of carbonic acid, to the presence of which in our rooms at night may be traced many of the ailments with which adults are afflicted. Six gas jets in a room of average size produce more deleterious effects on the atmosphere than thirty human beings, each jet consuming more pure air than five persons.

66

Moreover, a certain number of carbon particles pass unconsumed through the flame, and settle down in the form of smuts. These, and the fumes of sulphuretted hydrogen and carbon disulphide, given off by gas, blacken ceilings, wall paper, furniture, &c., and tarnish gilding, silver, &c.

"On the other hand, the incandescent electric light produces no such effects, for the reason that it is obtained by the heating to incandescence of a thin filament of carbon contained in a glass bulb hermetically sealed.

"There are some who object to the electric light on account of its coolness, and who say that gas is of service in a house for the purpose of heating the rooms. But when people realise that gas can only raise the temperature by distributing noxious fumes, they will prefer to heat their houses by more healthy methods."

Having quoted the remarks at the British Association of Mr. W. H. Preece as to the beauty and hygienic qualities of the electric light, the letter pointed out the convenience of turning the current on and off, and its steadiness, and then proceeded thus to refer to its beauty and safety :

66

Beauty. It is sometimes urged that a room never looks so well as when it is lighted by wax candles, or by oil lamps suspended from the ceiling, but though architects have been slow to treat the artistic arrangement of incandescent lamps, they are now awakening to the fact that they are capable of the most artistic handling. In themselves they are beautiful objects requiring little external decoration, and, where care is exercised, the most pleasing effects may be produced. They may be hung from the ceiling by silken cords, which conceal the wires conveying the current, or placed in the centre of sconces on the walls so as greatly to add to the artistic effect of the rooms. The wires conducting the electricity may be entirely hidden, but when exposed they are not more unsightly than the wires or cords by which pictures are usually hung.

"Safety.-Though the gas industry has been in process of development for more than fifty years, serious accidents through its use occur almost daily; indeed, the frequency of their recurrence causes little attention

333

to be paid to them, and the Press satisfies itself with very meagre reports of calamities which have long ceased to be novelties. Houses are frequently burned to the ground from the ignition of escaping gas, the upsetting of oil lamps, or the careless use of matches and candles. In the case of the electric light explosions and accidents of this kind cannot possibly occur.

"In the early days of the electric light much importance was attached by its opponents to the danger arising from the touching of wires conveying the electricity; but the incandescent lamps used in house lighting can only take a low tension current, which is absolutely innocuous. Not only so, but the wires are necessarily carefully covered throughout with an insulating material, making it impossible for any one to come into contact with them.

"With regard to the danger of fire, the insurance companies consider that premises lighted by electricity are much safer than those otherwise lighted. The lamps can be placed in any position and used in any place, even in close proximity to combustible materials, such as cambric, muslin, or bed curtains, without doing any harm and without incurring the slightest risk. If, by any accident, a lamp be broken, the oxygen of the outside air rushes in and instantaneously extinguishes the light before even the most inflammable material can be set on fire."

The special committee, in their report, also included a letter received from Mr. A. W. Slater, electrical engineer, giving his reasons for recommending that the vestry should undertake both the public and private lighting of the parish. Those reasons were :

"1. To keep the streets and roads entirely under the control of the vestry.

"2. To secure economy to the consumers, as all the office expenses, &c., of a public company would be saved, and to a certain extent the necessary work of collecting the rates, &c., would be done by the vestry's present officials.

"3. To enable any profit which might result to be used to reduce the ordinary rates on the whole parish, as is done in Belfast and other large towns in the case of gas lighting, and in this way attract new residents into the parish.

"4. The parish of Paddington being, perhaps, the wealthiest parish in London, it should be the most paying place for electric lighting, or, in other words, the light should be far cheaper than in any other part of the metropolis, if undertaken by the vestry, who have no directors or dividend to pay.

"5. In the case of gas lighting, is is almost invariably found that when the works are in the hands of the local authorities the quality of the gas is excellent and the supply very good. This should apply with regard to electric lighting."

Mr. Slater further stated that in such a populous and wealthy parish as Paddington he believed that electricity could be supplied to private consumers at a rate equal to 4d. to 5d. per Board of Trade unit, and that Paddington was particularly well suited for the supply of electricity from a central station.

The very important report of the special committee concluded with a copy of a letter addressed to the authorities of Hastings, Brighton, Eastbourne, Taunton, and Exeter for any information they could give on the subject, and the replies received from those bodies.

Mr. J. I. Minchin proposed: "That the report of the electric lighting committee be received, and that the same be considered at a special meeting of the vestry on Tuesday next."

Mr. W. Clarke seconded the resolution, and it was carried.

Electricity in Pennsylvanian Mines.-The New York correspondent of the Manchester Courier says that electricity will be shortly used as a means of traction at the bottom of the mines. At the Erie Colliery of the Hillside Coal and Iron Company in Forest City a dynamo has been fixed for this purpose, and the railway will shortly be inkoperation.

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INTERNATIONAL CONGRESS OF ELECTRICIANS HELD AT PARIS, 1889.

(Continued from page 307.)

Standards of Capacity.

THE standards of capacity are condensers graduated in microfarads and fractions of a microfarad; they are formed of sheets of tin, or sometimes tinfoil, alternating with sheets of some insulating material. This insulating substance varies according to the constructors; those most often employed are mica, paraffined mica, paper paraffined or covered with other insulating materials, and, lastly, ebonite cut into thin sheets.

The standards of capacity are as yet much more imperfect than the standards of electromotive force. They nearly all present, in a greater or less degree, three defects: 1, the charge is not rigorously in proportion to the difference of potential at the terminals; 2, they retain a residual charge; 3, the insulation is imperfect. Moreover, the capacity varies somewhat rapidly with the temperature.

When a condenser retains a residual charge its capacity is only clearly defined in two cases: that in which the discharge succeeds the charge with sufficient rapidity for the penetration of the electricity into the dielectric to be nil, and that in which the charge lasts sufficiently long for the penetration to have reached its maximum. But in the use of condensers it is often difficult to realise these conditions. In particular, if we wish to measure the charge of the condenser, on sending it through a galvanometer, by the impulsion of the needle, we use a formula which is only accurate if the discharge is produced in a sufficiently short time for the needle not to be appreciably displaced during its duration ; now this is not what takes place if the penetration reaches its maximum, the total discharge requiring a time comparable to that of the charge.

The only condenser that could really be considered as a standard would be a condenser with an air plate. Unfortunately, it seems difficult to realise conveniently condensers with a plate of air having a capacity of the order of the microfarad; two circular trays, 60 centimetres in diameter and 025 centimetres apart, form a condenser equal to about th of a microfarad.

The determination of the absolute value of a capacity in electro-magnetic units is most frequently effected. by methods in which the measurement of the capacity is reduced to the measurement of a resistance and of a time, such as the Maxwell method,* or its modifications, by J. J. Thomson † and R. T. Glazebrook, or else by methods in which the measurement of the capacity is reduced to that of a resistance and of a coefficient of mutual induction, such as that employed by M. Riöti in his study of various condensers that had figured in the Universal Exhibition at Antwerp.§

The measurements by M. Röiti and other physicists show that the real value of the capacities in commercial use rarely differs from their nominal value less than 1 per cent., and that often the error amounts to 4 per cent.

Before bringing this report on electrical standards to a close, we should like to make a suggestion. The standards of mutual induction, resistance and intensity of current, which we have called principal standards, because their absolute value can be determined independently, without having recourse to other electrical standards, possess, when properly constituted, an invariability comparable to that of a standard of length or volume. The necessity of fixing a legal standard of resistance has been recognised; why is it not the same with the two other principal standards?

The question is especially of importance as regards the intensity of currents, and now the way seems to be

[SEPTEMBER 20, 1889.

sufficiently paved for it. The International Bureau of Weights and Measures possesses already prototype standards of length, volume, and electrical resistance: everything seems ready for the adoption of a balance electro-dynamometer, which would serve as a prototype standard apparatus in the measuring of intensities, and with which the other instruments might be compared. The currents measured by the prototype electrodynamometer, according to the formula = A √ pj. in which A represents the constant of the instrumen: determined by measures of length, would be estimated by a conventional ampère, which would only differ from the theoretical ampère by a quantity certainly less than the difference between the legal ohm and the theoretical ohm; it is very probable that this difference would be less than oth. We should besides be able to control this error by the difference between the indica tions of this instrument, and those of M. Pellat's abso lute electro-dynamometer.

Many would think that it would be simpler for the comparison of currents, to indicate the mass of silver deposited in a second by an ampère. We may remark that the conventional ampère thus fixed would not be defined with sufficient exactness; electrolysis is, in fact, an exceedingly delicate operation, involving causes of relative error at least 10 times as great as the con parison of two balance electro-dynamometers. We will give the last results obtained for the electrolytic eqcivalent of silver:

Now the discrepancies which we note between the results in this table do not greatly exceed those which the same experimentalist finds in two electrolytic operations made under conditions as similar as possible as to measure of intensity, density of current, concentration of the solution of azotate of silver, &c. On the contrary, we have already said that the comparison of two balance electro-dynamometers can be made with a degree of precision within booth. This fact clearly shows the inconvenience of the definition of a conventional ampère based upon electrolysis.

10000

MEASUREMENTS OF ENERGY.

Report of M. A. POTIER.

Chief Engineer of Mines, and Professor at the Ecole Polytechnique.

At the time when dynamo-electric machines made their appearance in industry, the measurement of their rendering was of quite secondary importance and purely theoretical. We merely required from them services that a sufficiently powerful battery might have rendered. and their superiority from all points of view was 80 evident that little trouble was taken to measure it exactly; and even now, in a large number of installations the power expended by the machines intended for lighting is only a small fraction of the motive fores of the factory, the excess of expense corresponding to a smaller rendering of the dynamo is swallowed up in much greater expenses amongst which it disappears, and all that is required of the machine is absolutely regular working. Now that the applications have become more numerous, and the distribution of energy to a distance has been conceived, now that special motors have been created instead of utilising forces which were, so to say, superabundant, and a more active concurrence has arisen among the different types of

*Sitz. des Phys. med. Ges, zu Wurtzburg (1884).

+ Journal de Physique, 2nd series, Vol. I., p. 100 (1882), and Val III., p. 283 (1884).

Phil. Trans. of the R.S.L., Part II., p. 411 (1884). § Société Francaise de Physique, March 15th, 1889.

SEPTEMBER 20, 1889.]

machines, the rendering has become one of the factors of the commercial value of dynamos.

Thus it now becomes expedient to define this rendering exactly, and to agree as to the methods by which it is to be measured.

We will call the rendering of a dynamo machine, whether receiver or generator, the ratio of the available energy to the energy expended; the electrical energy will then be measured at the terminals of the machine; as to the work, it is desirable, in order to avoid uncertainties occasioned by the transmissions, that it should be measured on the axle of the machine.

The rendering of a motor can generally be measured with accuracy; except at very great speed, the employment of the brake will give very exact indications if we take the requisite well-known precautions concerning its sensibility and its tarage; the electrical measurements may be made with a yet closer approximation than that given by the brake. The rendering of a generator is also easily measured when we have at our disposal a proper transmission dynamometer; unfortunately these complicated and costly apparatus cannot be obtained at a moment's notice like brakes, their indications may be falsified if the speed exceeds certain limits, so that each apparatus works usefully only within somewhat narrow limits of power. Moreover, the dynamometers by which we measure the difference of tension of the two straps of the belt do not seem very exact.

It has therefore been sought to determine the renderings of generators without having recourse to these dynamometers, especially for machines of great power. We may proceed by substitution; after having taken at the Watt indicator the diagrams giving the work of the steam upon the piston at different rates of working and the electrical power of the dynamo, we replace this latter by a pulley with a brake on which we proceed in the same manner. Admitting that the rendering of the steam engine and of the transmissions remains the same, with powers and speeds that we endeavour to make as equal as possible, we have the elements necessary for the calculation of the rendering of the dynamo. When we have to do with a system of two machines, the determination of the rendering may be obtained by Messrs. Hopkinson's method: the two machines are mounted on the same axle and connected electrically like two batteries in opposition, so that one works as generator and the other as receiver; a dynamometer, which may be of low power, measures the work transmitted to the system of the two machines, work which is entirely absorbed by the passive resistances, the parasitic currents and the heating of the wires of the machines. This method has been modified by Mr. Revenshaw, who suppresses the dynamometrical estimation of the work transmitted. For this purpose a third dynamo is introduced into the circuit of the two first, and is worked by the motor. The power which it supplies is estimated electrically. If we designate as C this third machine, and as B and A the two first, which are mounted on the same axle, the measurement of the ratio of the differences of potential at the terminals of the machines, A and B, gives the rendering of the system A, B. Let R, be this rendering, we should in the saine way determine by the simple comparison of two electrical measurements the rendering, R2, of the system of the machines, A and C; and lastly, the rendering, R1, of the system, B, C. If we call 1 2 3 the individual renderings of the machines, and, supposing that they are the same in the three exR2, R3 periments, we shall get r2 = It seems doubtful R12 whether this method can lead to exact results, for the rendering of a machine varies with the intensity of the current that traverses it, and with its speed; it does not seem possible to make the machines work in these three experiments at their normal charge and speed.

M. Fontaine has employed a more simple method, also based upon the employment of three machines; the machine, A, is mounted on the same axle as the

335

machine, B; the latter works as receiver, the current is sent into it by a third machine, C, but the machine, A, is outside the circuit, B, C, and closed upon a circuit of resistance variable at will. The resistance of this circuit is so regulated that the current is the same as in the circuit, B, C; the ratio of the differences of potential at the terminals of the machines, A and B, still gives the rendering of the system, A, B. When the two machines are identical in construction, M. Fontaine assumes that the rendering of each is the square root of the total rendering; this amounts to assuming, as is done in the modes of proceeding derived from the Hopkinson method, that the rendering is the same whether the machine is a generator or a receiver; with this hypothesis, it would be easy, by making three experiments, to determine the individual rendering of each machine. The two methods (Ravenshaw and Fontaine) seem very satisfactory, at least for the rapid comparison of the renderings of machines of the same type tried successively; but from the moment that the equality of the renderings is assumed the employment of transmission dynamometers becomes useless, and the trial at the brake ought to suffice when it is required to determine the rendering of a single machine. One reservation is, however, necessary on this point; it is not allowable to say that the rendering is the same for two similar machines working under the above conditions. The rendering of the system of two machines may be nil, for example, without that of the receiving machine that it works being nil; it seems more rational to admit that with equality of the magnetic field of the inductor, and of current in the armature, the losses due to parasitic currents and other causes are the same if the speed is equal. In M. Fontaine's method, for instance, if 100 -x is the rendering of the system, B, A, formed of two similar machines, the rendering of the receiver, B, 200 should be and that of the generator, A, 100

200

200

200

x

To carry this reasoning further, if rendering of a receiver, its rendering as generator, 100 2 x

under the same conditions, would be 100

x

If experiments made with care confirmed these conclusions, no series of trials at the brake-trials which mechanicians consider as susceptible of very great precision-would be sufficient to determine the renderings of a generator in the various conditions under which it is required to work. It would then be interesting to know within what limits we may consider as equal the renderings or the losses of the same machine working as motor or as receiver.

In workshops where several machines are at one's disposal, it would always be possible to determine the rendering of a generator without employing any transmission dynamometer. Experiment has shown that up to 50 H.P. at least, the maximum power that I have been able to try, a receiver is an excellent dynamometer. If we measure at the brake the work furnished by the dynamo, we always find within the limit of error the same rendering when the machine works under the same conditions of speed and charge, although the electromotive force is susceptible of slight variations; the machine being in its normal condition as to greasing. We may then take a receiver, and for a series of speeds form a table of the rendering corresponding to a series of intensities; this graduation being made with all possible care, the trial of a generator would be made simply by coupling it on the axle of the receiver, and comparing the numbers of watts furnished and absorbed by the two machines. It is evident that this method would be equally applicable to the measurement of the rendering of an alternating current machine; it has the evident advantage that the forces applied to the machine to be tried are

336

reduced to a couple merely. By the suppression of the belts we eliminate the error, which it is impossible to estimate, arising from the variable tension of that organ of transmission, and which the employment of dynamometers allows to remain.

If, on the occasion of the Universal Exhibition, competent persons prepared themselves to exchange their views on this question of rendering, and could arrive at the fixing of some uniform rules, it would be a great advantage to the constructors of machines, and to those who use them.

TELEPHONY.

Report of M. de la TOUANNE, Telegraph Engineer.

Telephony has, by wonderful good fortune, spread in less than 10 years over the entire world, and the instrument, received at first as a scientific toy, has become the foundation of an industry that extends its domain from the village to the most flourishing towns. But the very rapidity with which this industry has been developed is in itself a source of danger. Hardly has one system been adopted when another more practical and more ingenious is conceived, and we see in such and such a large town a company, mindful of its good reputation and of the services that it has to render, relinquish a system that was hardly fully established, abandon installations only just completed, in order to arrange the organisation afresh from its very basis and create anew, in all its details, a system in harmony with recent progress. Such a determination is only very exceptionally necessary; and if, in smaller proportions, these difficulties are every-day ones, they might in many cases be avoided by more frequent consultations amongst those who are charged with these enterprises; questions concerning the lines, apparatus, central stations and tariffs take a hundred different aspects, and while feeling our way as we are doing at present, it would be of great advantage if competent persons could consult together upon the solutions already attempted and on those already acquired. As to lines, it seems as if the question of the conductor is almost decided. Little by little copper and its alloys are being substituted for iron and steel. But still it is necessary to determine in what cases it is certainly advantageous to know the results obtained under the most varied circumstances possible with bronzes, with hard copper, and with annealed copper. The latter, owing to its feeble tenacity, seems reserved for cables, but even these have probably not arrived at their definite form. A large number of types have been proposed; but what are their precise specifications, advantages, inconveniences? What is practically the limit of resistance, of capacity? How many wires is it expedient to unite in a single cable? What modifications must be adopted in the fabrication of the cable according to whether the system is one of simple wires or of metallic circuits? What information does experiment give us on this point? With regard to these metallic circuits, what are the devices of construction employed in overhead systems? Is it not possible, as has recently been proposed, to reduce the number of conductors and to employ a single return wire for a group of wires on the single distance. In this case, what arrangements must be chosen as regards the juxtaposition, on the same supports, of several similar groups, &c. These are questions to which we shall obtain no answer worthy of credence unless a certain number of practical men, resting as far as possible upon facts, will discuss them fully, and relate their failures as well as their successes.

The apparatus do not give rise to so many different questions that is, at least, if we abide by the results that are stated. Microphones, telephones, auxiliary sighals, come under only a few categories. The manifold models due to the fertility of imagination of inventors could only with difficulty be compared and classif; often the differences between them consist of il of merely commercial interest. The micro

som

[SEPTEMBER 20, 1889.

phones derived from the Hughes type have the very great advantage of being regulated once for all; those suggested by the Edison microphone are nevertheless retained in many systems; and lastly, the grain microphones were for a little while considered as an improvement. If the exact methods of measurement, now being studied, do not give, after a short delay, complete results, it will be desirable that the qualities of each kind, as observed by daily use, should be clearly stated. Telephones have also exercised the spirit of inven tion; the principle being known, the different forms of electro-magnets had necessarily to be tried; the inventors might frequently have even avoided presenting certain forms as new if they had consulted former works on electro-magnets, those of Nickles for example. In fact, at the present moment we believe that there are in existence several models of telephones very similar in value, and all good when they are well constructed. It is desirable, for the sake of future progress, that the exact relative influence of the parts constituting the instrument should be determined.

The auxiliary signals, bells, annunciators, &c., are modifications, sometimes happy, but not of capital importance, of telegraphic apparatus tried long ago. The same may be said of many combinations in which these accessories intervene-the Wheatstone bridge, differential mounting, &c., which have their origin solely in telegraphy; whether it a question of a Morse instrument, a bell, or an annunciator, there is no novelty in the matter. Innovation, which might be fruitful, appears very rarely, except in combinations where it is required to connect several consumers with the same wire of the central station, or in arrangements intended to procure communication with this latter automatically, after payment of the sum demanded for a conversation.

Amongst the accessories, one of the most important, the battery, is, perhaps, the one that leaves most room for doubt; the determinatiou of the most favourable element for transmissions would be useful.

With regard to the central stations, several points deserve special attention. In the first place there is the question of commutating tables; what facilities ought they to offer specially? For what number of consumers ought a central station to be furnished with that admirable system of multiple commutators which, coming originally from the new world, is gradually spreading over the old? These are elements, the knowledge of which is indispensable; the simplification and the certainty of the operations required of the employé are of capital importance when these operations are repeated several hundred times a day. The expense of the first installation then becomes secondary; indeed, often the greater part of the cost is more apparent than real. In any case, if it must be bought at the price of a temporary sacrifice, rapidity, which is the raison d'étre of the telephone, is the first thing to obtain. And the diversity of the systems is such, that, according to the type of table adopted, the number of communications established by an employé has increased from 200 daily to 200 an hour. These figures are not exaggerated, the maximum is higher still. Under these conditions, we can see that special care must be taken in the choice of material for a central station. Nevertheless, the fruit of this labour of installation would be partly lost if jndicious regulations did not ensure a good utilisation of it; it would therefore be very interesting to compare the regulations observed in the different systems, the instructions given, as much to the correspondents as to the employés, and to know the advantages or inconveniences which experience has shown in their application. To mention one detail only, in the New York system, every demand of communication is held to remain valid until it is satisfied; in the greater number of other systems it has to be renewed by the person concerned, when he has been informed that his order could not immediately be carried out. Of the two systems, the first gives correspondents an apparently incontestable advantage; but we must at the same time consider to what degree it impeded the service to the detriment of the fresh demands for communication :