iron pipe; the cause therefore was not mechanical, and a defect of manufacture or the effects of induction or charge must have caused a short circuit. In the last three it was not possible to define the cause with certainty, the iron and lead formed a molten mass; it is very probable that the accident should be attributed to the presence of organic matters in the soil. The new Friedrichstrasse cable was placed in a layer of clay. We remember, in this connection, that we laid in 1885, in a clayey mass, the electric cable which traverses the Grand Place at Brussels; it has remained absolutely intact to the present day. Without wishing to take part in this discussion, we will say that it appears to replace the asphalted jute insulator which separates the lead and iron by a more compact composition, which, while increasing the insulation, offers an opposition to the introduction of any humidity between the two sheaths, as also between the lead and copper. We have had a long experience, and are certain as to the manner in which India-rubber resists damp; but it is improbable that the insulator employed in Siemens cables, round the copper, is equal to India-rubber. The preservation of the leaden cover should therefore be complete and assured. The outer tarred covering appears to us not more than strong enough to guarantee the iron, when one reflects on the inevitable accidents which arise during the carrying and the laying, and, lastly, by the frequent excavations in the streets of a city. It would be preferable to dispense with this tarred covering, and to replace the iron spirals by a leaden sheathing of a certain thickness; then, to guarantee these cables against chemical action in laying them in a compact mass, clay or bitumen, and against the accidents arising from excavations in the streets, by means of a covering of thicker materials. We once used, with the latter object in view, simple tiles.

The

Long experience as to the manner in which, under public thoroughfares, iron or lead branches behave, induces us to say that an iron armature for electric cables is an excessive precaution against mechanical shocks, and, on the other hand, insufficient against chemical deteriorations. The oxidation of iron in the soil is very rapid, whatever the precaution taken to preserve it. It appears that at Paris what are called Flemish tubes are used. These are of fir balks, more or less deeply grooved, and closed by a lid. The wood used is subjected to an injection of sulphate of copper. A similar means has been employed in America, the wood being creosoted. It was found, however, that the creosote attacked the lead, which caused it to be replaced by sulphate of copper. When there are a certain number of cables, small cement drains are used in Berlin, in the interior of which are placed the naked conductors, borne by insulators. drain is made by partitions in cement 4 or 5 centimètres thick, the core of which is a trellis of strong iron wire. The experience of these cement canalisations is not sufficiently advanced to allow of an estimate to be formed yet. At Paris, also, naked conductors are employed in conduits of cement. The armed conductors at Berlin were in the earth at a slight depth. street crossings there were, as junctions, large square metal boxes, 75 centimètres long by 25 centimètres high, furnished with tubes for the passage of the cables. These boxes are completely filled with an insulating oil, and closed by a bolted lid. The branches are made by means of smaller metal boxes of an elongated shape, and on an analogous system. The general potential in the line of distribution is 100 volts. In order to determine the dimensions of the cables, and recognise the necessity of an auxiliary cable or feeder of the line of supply, the central bureau has constructed in miniature a similar line to the real line, in giving exactly to all the conductors a proportional resistance to the real resistance. By this means, as soon as the delivery increases at one point of the line beyond the limits anticipated, account is easily and exactly taken of the modifications it is necessary to make. We enquired as to the manner in which the project for electric lines in Berlin was drawn up. Several diagrams were traced relative--1. To the consumption of gas; 2. To the

At the

[JULY 19, 1889.

number of burners in use; 3. To the number of burners placed; 4. To the assessment of the land tax paid by the inhabitants. This work was done street by street, and from the combination of these different diagrams a total diagram has been deduced. This was, however, only a first indication, from which it was necessary, in reality, to deviate now and then considerably. A circular was addressed to the inhabitants asking them for useful information relative to lighting and motive power; this circular was accompanied by a tariff showing the conditions on which the electric currents would be supplied.

The most practical means, according to the Berlin engineers, was to found their basis almost exclusively on the number of gas burners lighted at once in important establishments. For private houses a lamp or a half lamp per lineal mètre of street was allowed, according to the class of the street. As to the establishments which have their own installations of electric light, Berlin prices are so far favourable that the addition of the greater number of these installations to the general line is looked for at no distant date. The supply of the electric current is continued during the 24 hours of the day. It is measured by Aron meters, the working of which appears to be satisfactory. During the night a single station performs the service of the whole line. Towards the evening the supply increases very abruptly; the curve of the ampères varies in a more considerable proportion than that known for gas. The present actual supply (November, 1888) of the Berliner Elektricitäts Werke Company is 2,200,000 watts, or the equivalent of 36,000 16-candle-lamps. A third of this total is taken by arc lamps. These figures do not include the Kaiser Galerie Station nor private installations; among the latter there are several theatres. The Berlin gas administration gives in its annual reports some information on the whole position of the electric lighting of the city. We take therefrom the subjoined figures :

For the application to electro-motors a remission of 25 per cent. is granted when the subscriber instals a special meter.

The applications of electricity as a motive power appear likely to become of importance. A steam motor or a gas motor do not work, in general, so economically as when they work at full charge. Thus, in a printing office, the fire must be kept up and the boiler must work as well for one machine as for 10. With the electric current small electro-motors can be applied to each machine, if wished, and only the motors requisite need be worked. The prime motor and numerous transmissions are done away with; no mechanic or boiler is wanted. The Berliner Elektricitäts Werke balance sheet for the period ending June 30th, 1888, its fourth year of existence, showed a profit permitting the distribution of a dividend of 5 per cent. on the share capital of 3,000,000 marks. We notice in this balance sheet the following figures for the different redemptions -Personal property, 15 per cent.; appliances, 40 per cent.; lands, per cent. ; engines, 15 per cent.; canalisation, 4 per cent. There was also carried 2 per cent. of the net receipts to the renewal fund and 5 per cent. of the profits to the reserve fund. The contract by which the City of Berlin has conceded the working to the said company is a non-exclusive concessionthat is to say, the city simply grants authority to utilise the streets for laying the cables. The annual rent to be paid by the company is 10 per cent. of the net receipts, plus 25 per cent. of the net profit exceeding 6 per cent. on the capital employed. The concession is granted for 30 years, but the city can purchase it after October 1st, 1895, on certain conditions. The security deposited by the company was 25,000 marks.

The public lighting of Unter den Linden is one of the most successful installations. Arc lamps of 15 ampères, enclosed in opal globes, are placed 40 mètres apart and 8 metrès in height, along the footways. In the promenade, which occupies the central part of the thoroughfare, the lamps are suspended to chains, attached each side to candelabra. The latter are of a very artistic model, decided upon after a competition. instituted by the city. The number of arc lamps is 108. For the service, the lamps are lowered by the aid of a cable with a counterpoise, placed inside the candelabrum. The conductors rise in the candelabrum midway; thence they are visible and movable so as to allow of the working of the lamp. The reflector is fixed and protects the globe against rain and snow. The lamps are placed in series on nine different circuits, fed by dynamos placed at the central stations ; five circuits work up to midnight only. The extinction of all the lamps of a circuit would present no serious inconveniences, the circuits being alternate. The extinction of. a lamp introduces, moreover, an equivalent resistance, so that the chances of the total extinction of a circuit are much reduced. We gathered no unfavourable information on this point, save in the offices of the city's gas service, where we were told that one or two general extinctions of the whole lighting had occurred. On account of the great number of separate circuits, worked three by three, by completely independent motors, general extinction is an evident impossibility, and we regard this information as erroneous. We hope one day to see our boulevards (Brussels) lighted thus. What proves the incontestable superiority of electric lighting over gas lighting in large streets and public places is the lighting of the façades. With gas the houses remain in great darkness, broken in some places by light from the lamps. With the electric

light, on the contrary, the whole street is illuminated, and the houses appear throughout their height in the light, which recalls the aspect of the street during the day. The electric light will certainly produce the happiest effect with the white and neat façades of our Brussels houses. The old gas burners have been replaced on our boulevards by intensive burners. Many persons have not noticed the change, and yet the present lighting is five to six times stronger than the primitive lighting. Apropos of extinctions, Berlin has not yet dared to dispense with all precautions. Everywhere the lustres have retained their gas burners, either the old ones or new ones. But another reason than the fear of extinction guides the proprietors of public establishments; that is, that in winter the warmth produced by the burning of gas is very favourable to the rapid warming of rooms. During the evening, when the temperature has risen, the gas is put out and the electric lamps lighted. At Berlin, it is becoming more and more the fashion to place arc lamps outside the large shops, occasionally in considerable number, fixed on candelabra or hung to ornamented consoles. The shop of the Allegemeine Gesellschaft, in the Friedrichstrasse, is very interesting to visit. Besides a large collection of lustres for electric lamps, saw there electro-motors for small industries, notably, sewing machines, &c.

we

(To be concluded.)

A PECULIAR GROUND.*

By W. L. P.

A SHORT while ago an incident happened in connection with the Edison three-wire system under Boylston Street, Boston, which is interesting both to the electrician and the chemist. It was noticed that the horses were very uneasy and somewhat scared when passing over an area of, say 10 feet square, in the granite pavement of the street. An investigation by the Edison people seemed to show no trouble, and everything went right for ten days or more, when, during a rain storm, the same action of the horses was noticed.

Upon digging down to the wooden box which contained the three wires of the system, embedded in some kind of tar or bitumen compound, a spot was found where the box was eaten through, and a large mass of sticky stuff was found around the negative wire. The insulation of the wire was destroyed, and as the neutral is dead grounded in the station there was a leakage, causing a fall of potential in the earth about the leak which was sufficient to affect horses as well as men. The leak was a small one and did not show at the station.

Chemical examination of the lump showed that it was originally concentrated lye which had become partly converted into caustic soda by water, and that the action of the currents had, by electrolysis, formed a considerable quantity of metallic sodium throughout the mass. There was sodium enough present to make a fair display of fireworks when thrown into a pool of water, and it is fortunate the workmen did not get into trouble in handling it.

My theory of the affair is this: In some way a piece of lye tumbled into the kettle in which the insulating compound was made and was not noticed when the box was filled. In time surface water got at this lump and converted a part into caustic soda, which destroyed the box and insulation of the wire (it only came in contact with one wire, the negative).

The escaping current caused a difference of potential at the surface of the ground which disturbed the horses. Metallic sodium was set free and would tend to collect at the negative wire.

The voltage at the escape was in the neighbourhood of 105 volts, and it was estimated by the touch that there was over 50 volts within the space that a man could reach with both hands.

Electrical World.

64

THE TESLA SELF-STARTING ALTERNATING MOTOR SYSTEM.

As is well known, certain forms of alternating current machines have the property, when connected in circuit with an alternating current generator, of running as a motor in synchronism therewith; but, while the alternating current will run the motor after it has attained a rate of speed synchronous with that of the generator, it will not start it; hence, where these "synchronising motors," as they are termed, have been run, some means have been employed to bring the motors up to synchronism with the generator before the alternating current of the generator is applied to drive them. In some instances mechanical appliances have been utilised for this purpose. In others, special forms of motor have been constructed.

With the object of effecting the starting of the alternating motor and bringing it to synchronism without external aid, Mr. Nikola Tesla has devised a simple system in which he employs an earth return during the period of starting only. For this purpose he constructs a generator with two coils or sets of coils and a motor with corresponding energising coils or sets of coils. By means of two line-wires, one terminal of each generator coil is connected to one terminal of its corresponding motor-coil, while the opposite terminals of the generator-coils are joined together, and likewise those of the motor.

F

H

To start the motor an electrical connection is temporarily established between the points of connection, between the coils in the generator and those in the motor, so that the system becomes an ordinary doublecircuit system. When by this plan of connection the motor has attained the desired speed, the earth connection is severed, by which means the system becomes an ordinary single-circuit synchronising system. The accompanying diagram from the Electrical World shows the manner in which this is accomplished, G representing an ordinary alternating current generator having four field poles, A, magnetised by a continuous current, and an armature wound with two coils, C, connected together in series. M represents an alternating current motor with, say, four poles, D, the coils on which are connected in pairs and the pairs connected in series. The notor armature should have polar projections and closed coils, E.

From the common joint or union between the two coils of both the generator and motor an earth connection, F, is established, while the terminals or ends of the coils which they form are connected to the line conductors.

Assuming that the motor is a synchronising motor, or one that has the capability of running in synchronism with the generators, but not of starting, it may be started by the above-described plan by closing the ground connection from both generator and motor. The system thus becomes one with a two-circuit generator and motor, the ground forming a common return for the currents in the two line wires. When by this arrangement of circuits the motor is brought to speed, the ground connection is broken between the generator or motor, or both, and ground switches, K, K, being employed for this purpose. The motor then as a synchronising motor.

[JULY 19, 1889.

A SYNTHETIC STUDY OF DYNAMO MACHINES.

(Continued from page 11.)

VI. ARMATURES IN PRACTICE-(continued). 22. Armatures of Class 3 Machines.-In former articles we have treated of the armatures of Class 1 machines in which the current supplied to the outside part of the circuit is alternating in direction, also in later articles of the armatures of Class 2 machines in which the current is in the same direction but of a pulsating character. We have now to deal with the armatures belonging to machines of Class 3, which yield currents practically of steady flow.

In the machines of the second kind, which have occupied our attention in the last three articles, the total E.M.F. is the added E.M.Fs. of a few coils which may be always in circuit or thrown into the circuit only at regular intervals. Though these coils may be arranged in such a way as to make the fluctuation of the resultant E.M.F. a minimum by their positions of greatest activity occurring in regular succession, it will be obvious that the E.M.F. cannot be of uniform value unless the armature contains a large number of such coils. It is quite conceivable that we make a dynamo having on its armature 36 coils, wound in twice as many sections, instead of the two coils wound in four sections, as shown in fig. 111. Such a machine would undoubtedly give an E.M.F. practically uniform; but when we reflect that if constructed with split-ring commutators it would require no less than 36 of them, having as many pairs of brushes connected in series, we see at once that the mode of construction is impracticable, and that for the collection of currents from machines which are to give a uniform E.M.F., some simpler device must be resorted to. But that this device must be in some way equivalent to a number of commutators, such as we have described, is also apparent.

We have seen that the E.M.F. induced in each coil or section is in a two pole machine reversed in direction twice per revolution; and from this it follows that in all the active wires extending over half the circumference of the armature, the E.M.F. is induced in the same direction, while in all the wires extending over the other half, the induction is in the opposite direction. This is true so far as the conductors are concerned, whatever the number of coils or sections and however connected to the commutator. In the diagram, fig. 118, N and S are north and south poles,

A being the armature core and the small circles on its exterior representing the active wires. The motion of the armature being in the direction of the arrow, all the conductors on the half circumference, a, c, b, will have the induction in such direction as to send a current into the paper, as shown by the black circles while in the wires on the half circumference, a, d, b, the induction will be such as to make a current flow in the opposite direction, as shown by the white circles. A section may, of course, consist of any number of these conductors connected together.

The function of the commutators, shown in fig. 111, is

character to that obtained from one coil of the arrangement in fig. 111, but the E.M.F. is now halved, since it is due to one section only instead of two in series. Double the current could, however, be carried by this arrangement. Now, imagine that the whole of the ring is wound over with wire in a large number of sections lying close together. If constructed with split ring commutators there would be for each of the two sections, on diametrically opposite sides of the ring, one commutator, and the arrangement might be represented as at fig. 120, where A, B, C, D, E and F represent the six adjacent commutators for an armature of twelve sections, G, H, J, K, L, &c., being six adjacent sections occupying half the circumference of the armature. The connections of the sections to their respective commutators are clearly shown, and for each commutator there is one pair of brushes marked 1, 2; 3, 4; 5, 6, &c., the pairs being joined in series, 2 with 3, 4 with 5, and so on. The circuit through the armature

Fig. 121.

In figs. 120 and 121 the armature winding is in two parallels, the E.M.F. being that induced by half the exterior wires connected in series. This is rendered more clear in fig. 122, which shows the armature with its 12 sections joined up to 12 commutator bars, and also the collecting brushes, A and B. It will be seen that just at the moment when the direction of the induction is reversed in a section, the bars terminating its ends pass under the brush, its connections relatively to the brush being consequently reversed. The current splits into two equal portions, half going through each half of the helix, as shown by the arrows. That there is no essential difference between the arrangements shown in figs. 120 and 122, will now be apparent. But for a large number of armature sections the latter construction is essential, while for an armature having few coils the former is most suitable.

N

A

has its terminations at brush 1 and brush 12. Clearly the function of the intermediate brushes is to connect the sections together that they may all combine to send the current in the same direction. Brush 2, for instance, being connected to brush 3, joins the end of section H with the beginning of section J, while 4, being connected to 5, joins the end of J with the beginning of K. The combination of commutators and brushes has the effect of converting the winding of the armature thus composed of sections into one endless helix, and that the E.M.Fs. of the separate sections may be added, it is only necessary that the segments terminating the ends of diametrically opposite sections should be brought under the brushes when these sections occupy in the magnetic field the position of reversal. For the complicated arrangement in fig. 120 we can substitute a much simpler device, which will fulfil the essential condition of reversing at the right moment the connections of the section to the external part of the circuit. This device consists in substituting for these split ring commutators a number of parallel bars, as shown in fig. 121. These are carefully insulated from each other, and form, when laid together, a polished

THE ELECTRIC LIGHTING SCHEMES.

Petitioners Before the Commons Committee.

LONDON ELECTRIC SUPPLY ORDER GRANTED.

ON Tuesday last, before the following Select Committee of the Honse of Commons: Sir George Trevelyan, Sir H. Roscoe, Mr. Duncombe, and Mr. StoryMaskelyne, a considerable number of petitions were heard against the Bills which had been read a second time, and under which Provisional Orders for electric lighting had been granted by the Board of Trade. By these Orders power was given to the London Electric Supply Corporation, Limited, to light the parish of Chelsea, part of St. Mary Abbot, St. George's, Hanover Square, St. James's (Westminster), St. James's and St. John (Clerkenwell), part of St. Martin-in-the-Fields, part of St. Margaret and St. John the Evangelist, part of Lambeth, part of St. Mary, Newington, and the districts of St. Saviour, St. Olave, Rotherhithe, Bermondsey, and Greenwich. The Order of the Westminster Electric Supply Corporation comprised the area of St. George's, Hanover Square, and part of St. Margaret and St. John (Westminster); that of the Electricity Supply Corporation, Limited, included the parish of St. Martin-inthe-Fields; that of the House-to-House Electric Supply Company, Limited, gave power to lay mains in the parish of St. Mary Abbot, Kensington; that of the Kensington and Knightsbridge Electric Lighting Company, Limited, also to light a portion of St. Mary Abbot and the parish of St. Margaret, Westminster, to the west of St. George's, Hanover Square; that of the Notting Hill Electric Lighting Company, Limited, to light also a portion of the parish of St. Mary Abbot, Kensington; that of the Chelsea Electricity Supply Company, Limited, to light certain large squares and crescents in South Kensington; to the Metropolitan Electric Supply Company, Limited, was apportioned for lighting the parish of Lambeth and the parts of the parishes of Streatham and Clapham, in Wandsworth, the St. Giles (Bloomsbury), Holborn, and Strand districts, and the parish of St. Marylebone. Two important provisions in the Orders are as to overhead wires and the protection of telegraph and telephone companies. The first is: "The undertakers shall not, without the express consent of the County Council, place any electric line above ground, along, over, or across any street or public place, or (except in the case of any electric line so placed by themselves before the commencement of this Order, and during the time limited by this section for the removal thereof) supply energy by means of any electric line so placed. Seven days before commencing to lay down any electric line, or to supply energy through any electric line, in any manner whereby the work of telegraphic or telephonic, or electric signalling, communication through any wires or lines lawfully laid down or placed in any position may be injuriously affected, the undertakers shall, unless otherwise agreed between the parties interested, give to the body or person for the time being entitled to such wires or lines notice in writing specifying the course, nature, and gauge of such electric lines, and the amount and nature of the currents intended to be sent along the same, and the extent to and manner in which (if at all) earth returns are proposed to be used; and the undertakers shall conform with such reasonable requirements as may from time to time be made by such body or person as aforesaid for the purpose of preventing the communication through such wires or lines from being injuriously affected as aforesaid."

The counsel in this case were Mr. Pember, Q.C., Mr. Moulton, Q.C., Mr. Loyd, and Mr. Graham for the London Electric Supply Corporation; Mr. Pope, Q.C., Mr. Bidder, Q.C., and Mr. Danckwerts for the St. Margaret's and St. John's (Westminster) Vestry; and Mr. Freeman on behalf of the London County Council.

Mr. PEMBER opened the proceedings by saying a few words as to the procedure in the cases before the committee, and then explained the area which the London Electric Supply Corporation was authorised by

[JULY 19, 1889.

the Board of Trade to light. There would, he said, have been no opposition to the preamble of his Bill had it not been for the united parish of St. Margaret and St. John, Westminster. The capital of the company was a million and a quarter, of which £800,000 was subscribed, and £500,000 or £600,000 was paid up, and a half of that was spent. They began operations by taking the Grosvenor Gallery station, from which they supplied more than 33,000 lights. The experience gained there had led them to the conclusion that it was a bad thing to have generating stations in populous neighbourhoods. Their intending system, therefore, was to have one large generating centre outside London, at Deptford, with trunk mains coming up along the railway companies lines and over the bridges carrying the electricity at a very high pressure to local stations inside London, where the high pressure would be converted into a low tension, and the distributing mains, which would carry it from the conversion stations along the streets, would be connected by wires to the houses of consumers, where it would be converted again into a handy pressure, so as to enable it to be laid on to different rooms in the house. The system of lighting adopted by the London Company was the alternating system as opposed to the direct system of storage batteries. The new feature of the London Company's adoption of the alternating system was the generation of the electricity and its first distribution at a very high pressure indeed. The pressure in their trunk mains was a pressure of 10,000 volts at the converting station. The pressure was altered by a well-known instrument called a converter to a pressure of 2,500 volts, at which it was carried along the streets in the distributing mains. Wires then went off to single houses or buildings and the 2,500 pressure was reduced to 100 or 50 as it was required in a handy form, and there would be one converter for every 10, 20 or 30 houses. One of the great contentions of his company had all along been that they had never asked for an exclusive grant of an order to light any district, for they had never opposed competition. They were quite ready for any other company to come in provided his company was not excluded, for theirs was the best system, and the one which the customers would ultimately adopt. His company feared no competition and desired no favour. Mr. Pember proceeded to deal at length with the petition of the parish of St. Margaret and St. John the Evangelist, and was speaking of the crossing of Westminster Bridge, whereupon

Mr. POPE urged that it was stated that the crossing of Westminster Bridge as proposed was neither practical nor desirable.

Mr. PEMBER replied that he knew that the London County Council would ask for a clause prohibiting the use of any bridges unless the work was carried out in a manner approved by their engineer. He would contest their right to such a clause, although his company was perfectly willing to submit the matter to an independent arbitrator, supposing the work was not done satisfactorily by their own engineer. The provisional orders, Mr. Pember continued, did not grant any monopoly of lighting, so that the request of the opposing local authority for a postponement of the lighting of the united parishes of St. Margaret's and St. John was not necessary. The parish authorities did not want the electric light to be admitted into their parish.

Mr. POPE: They never said so, and do not think so. But they do object to this order.

Mr. PEMBER: They asked that the order should stand over for a year for further consideration. If that is not a refusal to admit the electric light into the parish I do not know what is. Mr. Pember then alluded at length to the following clauses in the petition : "Your petitioners humbly submit that the effect of the bill will be to authorise considerable interference with streets and thoroughfares under their control. Part of their parish will be allocated in connection with another area of London to the London Company, and part will be allocated to the Westminster Company.

"Your petitioners have no reason to believe that any considerable demand exists at the present time for the