example of the five-wire system in England, the Manchester installation will have great interest for electrical engineers. Consulting Engineers.-Messrs. Morgan Williams and Frank King, whose commencement as consulting engineers we announced last week, are acting in this capacity to the Sydenham electric lighting station, now being carried out by Messrs. J. E. H. Gordon and Co., Limited. We believe they are also engaged in investigating and reporting upon a scheme for lighting a tunnel two miles long on the Rhondda and Swansea Bay Railway, and for lighting the trains by the use of neighbouring water power.

St. Helens.-Tenders are invited for erection of certain appliances and machinery for the supply of electricity to the Town Hall, St. Helens. Plans may be seen and specification and form of tender obtained on application to Mr. G. J. C. Broom, A.M.I.C.E., the borough engineer, on payment of one guinea, which will be returned on receipt of a bona fide tender. Sealed tenders to be sent in Sealed tenders to be sent in by 21st inst., addressed to the Chairman of the Parks, Markets, and General Purposes Committee, and endorsed "Tender for Electric Light, Town Hall."

Blackpool. The Blackpool town councillors are determined to do something practical with reference to the electric lighting question at once. At the last meeting Councillor Pearson was appointed chairman of the Electric Lighting Committee, and it was resolved that a short statement of particulars of electric lighting in selected towns be prepared under the directions of the chairman, Councillor Sergenson, and the town clerk; also that those members of the committee who can make it convenient should visit the towns so recommended by the sub-committee.

Fatal Accident at Lauffen.-We regret to learn that on Monday one of the engineers employed at the Lauffen generating station met with a fatal accident through touching a wire through which a high-tension current was passing. The deceased, whose name was Rau, was discovered lying dead on the floor of the transformer-house by the engineer-in chief. It appears that Rau, in defiance of the instructions given him, entered the transformer-room to attend to a defective lamp, and coming into contact with a high-tension wire was killed instantaneously. Jensen Electric Bells. We are informed by Messrs. Woodhouse and Rawson United, Limited, that Messrs. Hans Jensen and Jens Jensen, hitherto branch managers of the business carried on at 2, Gray's-inn-road, under the name of the Jensen Bell and Signal Company, are no longer connected with the company directly or indirectly. The whole of the patents are the property of Woodhouse and Rawson, and the bells will continue to be manufactured as before. It is intended to remove the business to the Cadby Hall Works, Kensington.

Telephone Charges.—A correspondent in the Scotsman, referring to the application of the Caledonian Telephone Company, of Glasgow, for a license from the Post Office to run telephone exchanges, expresses a hope that the license will be granted, as the public will then have the advantage of cheapness and efficiency, these coming with competition. He mentions that in Paisley an exchange connection is obtainable for £5 a year, and where two people use the same wire, each having their own instrument the expense is the mere trifle of £3 a year each.

Ulverston.-The Ulverston Local Board would probably be grateful for a little definite information as to the cost of electric lighting. It is necessary to do something to keep their provisional order, but they do not wish to absorb the dwindling profits of the gas works. One member expressed an opinion that electric plant for Ulverston

would cost £100,000! With the use of water power one or two thousand should do a great deal. The clerk is to communicate with the Board of Trade, and report again as to the steps to be taken to put the provisional order in force.

Teaching Languages by Telephone.-What are we coming to next? The question of teaching languages must indeed be pressing, if what is stated is not a joke. The French Minister of Public Instruction-noting that in learning English it is the pronunciation that is the most difficult part has decreed, in accordance with arrangements made with the Minister of Posts and Telegraphs, that after the 15th October the Paris-London telephone line is to be placed at the disposal of students of languages. Other international lines as erected are to be used in the

same way.

Sherborne.-Mr. E. R. Dale has been exhibiting the Maquay system of lighting by primary batteries with considerable success, fitted up in a tent at the rifle camp and at the water works, Sherborne, Dorset. An instance of the extended demand for small lamps is given in the fact that one firm ordered this week over £200 worth of the Maquay bicycle lamps. Mr. Dale is, we understand, fitting up a dynamo and waterwheel in another part of the town, and is also intending to hold a local exhibition with an improved gas engine, dynamos, and electric fittings. Exhibits on commission will be included of other makers' goods.

Fire at Bournemouth Telephone Exchange. It is not often we manage to set telephone exchanges on fire in England, but a case happened during the recent storm. About nine o'clock on Tuesday night a fire suddenly broke out in the switchroom at the Bournemouth central exchange of the Western Counties and South Wales Telephone Company. The whole apparatus became suddenly alight, and the night operator states that he had a narrow escape. He attributes the fire to the contact of the overhead electric lighting wires, caused by the boisterous wind that was prevailing. The fire was extinguished.

Grays (Essex).-The Grays Local Board have before them the question of improvement in the town lighting, and a report has been furnished by Mr. A. W. Boatman and Mr. J. Golden. The ternis offered by the gas company were considered too high. The committee think it would be advisable to have the entire control of the lighting under the Local Board, and suggest that, as the Board are about to erect a pumping station for the sewage works, it might be well to erect machinery at the same time and light the town by electric light. The question was adjourned, and a copy of the report was ordered to be sent to the gas company.

Another Blackpool Tramway.-Blackpool is to have another electric tramway, if proposed plans are carried out. At the last meeting of the Blackpool Town Council a letter was received from Mr. C. Chadwell, engineer, of Blackburn, enclosing plans showing the route of the proposed tramway for submission to the Highway Committee. The tramway will commence at Lytham and pass through St. Anne's to Blackpool. The cars will be worked by electricity or the cable system. It is intended to apply for a provisional order next session to construct and equip the tramway, and the Council are asked to assist by assenting to the Bill for obtaining the powers.

Sunderland.--At a special meeting of the Electric Lighting Committee of the Sunderland Corporation, held last Friday, the returns were presented from some eight or ten towns in which provisional orders had been obtained for electric lighting, and some of which had been in negotiation with private companies to take over the supply. None of them, however, had come to any definite arrangement.

After a long discussion it was decided to write to the various large electric lighting companies informing them that the Corporation were open to treat, and asking upon what terms any of the companies would be prepared to take over the powers of the Corporation for a limited number of years. The committee will be called together again as soon as these replies have been received.

Glasgow Library.-Bailie Martin asked a question at the Glasgow Town Council meeting last week with reference to the gas engine supplied to the Mitchell Library for the electric lighting. According to the standing orders of the Town Council no member is allowed to contract directly or indirectly for the Corporation, and he wished to know how a member had got his gas engine into the library. It was explained that the Gas Committee provided the installation, the specification being drawn up by Mr. Cook, the electrical engineer consulted by the committee. The firm who obtained the contract put in an Acme gas engine, which Councillor Burt was interested in. It was not decided whether this fact raised any legal question, and the decision of Sir James Marwick was promised for next meeting.

Efficiency of Accumulators.—In a paper before the Berlin Electrotechnical Society, Herr Ross gave some interesting particulars of the efficiency of accumulators used in the central electric light stations at Barmen, Dessau, and Darmstadt. At Barmen, after one year's service, the efficiency fell to 37 per cent.; repairs to the battery brought it up to 56 per cent. This is bad, but better figures were obtained at Dessau, where, exact measurements having been taken by meter, the cfficiency was found to be 85 per cent. The accumulators at Darmstadt only supplied 12 per cent. of the whole output, and the mean efficiency in watts is given as 39 per cent. in 1889; this rose to 60 per cent. in 1890, after a partial overhaul of the cells. These figures show that accumulators (at any rate as used in Germany) are far from perfect, though the mean percentage at Barmen would almost seem to result from some error in measurement. When will our engineers give us similar figures of their accumulator efficiencies ?

Walsall Electric Tramway.-At the meeting of the Walsall Town Council on Monday, the General Purposes Committee reported that they had appointed Mr. F. Brown, of the Walsall Electrical Company, to advise as to the terms and conditions upon which the South Staffordshire Tramways Company shall be allowed to erect their overhead wires and work their tramways within the borough by means of electricity, and to superintend the carrying out of the of the works so as

to

ensure proper precautions for the safety of the public; and they recommended that the company be allowed to use steam 12 months longer on their lines within the borough, with a view to enable the company to equip their lines for electric traction before the expiration of that period, and that the sum of £500 be accepted from the company in discharge of their liability to repair and maintain the wooden pavement in Bridge-street. The report and recommendation were adopted.

Nelson (Lancs.). At the monthly meeting of the Nelson Town Council last week the report of the Gas Committee came before the Council. The gas engineer had made a partial and satisfactory canvass of probable customers. The Gas Committee recommended that the town clerk have full authority to prepare agreements for guarantors and also to make application to the Local Government Board for such borrowing powers as might be considered necessary to put in force within the borough the provisions of the provisional order, and the committee recommended the borrowing powers to be fixed at £10,000

Councillors Sunderland and H. Dyson were added to the electric lighting sub-committee. It was stated that the town clerk had been instructed to obtain information as to cost of central station. The minutes were confirmed, and a resolution was passed empowering the town clerk to make application for the sum mentioned for electric lighting purposes.

Bombay. At a recent meeting of the Corporation of Bombay, says the Bombay Gazette, a long discussion arose on the proposal to experiment with a view to ultimately lighting Bombay by electricity. Mr. K. N. Kabraji moved : "That the Commissioner be authorised to invite fresh tenders for electric lighting, as an experimental measure, including a clause for the continuation of such contract as may be agreed upon, or for the purchase of the contractor's plant in the event of the installation proving successful, such lighting being from the Arthur Crawford Market Tower along the Esplanade and Hornby roads to Apollo Bunder, including lighting that market, Church Gate-street, Elphinstone Circle, and the Rajabai Tower." Dr. Balchandra then moved as an amendment that the consideration of the question of electric lighting be postponed, pending the question of the liability of the Corporation as to the cost of the police and other matters being settled, which, on a vote being taken, was carried by 20 to 14.

Electrical Specialities.-A company has lately been formed, under the title of Munro's Electrical Manufacturing Company, Limited, of 9, Holland-place, Glasgow, for the manufacture of electric apparatus and fittings and the carrying out of new inventions. With reference to the latter department, they have a staff of skilled workmen trained for this class of work, having lately worked out and perfected several important and complicated pieces of mechanism. They are open to take up and develop inventions at any stage, and enter into arrangements with inventors. With reference to the fitting department it is found that for the better class of installations, particularly in country mansions, there is a demand for designs which will not be seen in every second or third house visited, and which are not to be found in trade lists. To satisfy this want, special designs are produced, which will not be placed in lists, of highest design and workmanship, and of real handwrought hammered work. Mr. John M. Munro, M.I.E.E., is managing director of the company, and Mr. David Alexander, A.I.E.E., secretary. They have offices in Newcastle, Liverpool, and London, the latter being at 45, Jewinstreet, E.C.

Oil Engines. -Electrical engineers may be interested in hearing that orders for Priestman's patent oil engine continue to be received freely for a large variety of purposes. Amongst these may be mentioned an 18-h.p. engine for Messrs. Palmer's Shipbuilding and Iron Company, Limited, besides orders from the Great Western Railway Company, Mr. T. H. Ismay, and others for printing, sawing, and electric lighting. For the past two or three years Messrs. Priestman, at their Holderness Foundry, Hull, have been fully occupied developing oil engines of the horizontal and portable types, and they are now in a position to supply the marine type of oil engine, suitable for propelling launches and barges. Some time ago the authorities of the Manchester Ship Canal (Bridgwater section), after carefully investigating the merits of the system, took a small engine on trial, and after testing the working of this thoroughly, they were supplied with two pairs of 10-h.p. engines, which have now been in regular use for some months. The Grand Canal Company of Ireland, after inspecting these engines, have also ordered engines of a similar size. We understand that a launch, 28ft. by 6ft. by 3ft. 6in., fitted with a pair of 5-h.p. engines, can be inspected at Hull by

appointment. Oil engines for private country lighting are being largely supplied.

Preston. The Preston electric lighting company have recently acquired a portion of a cotton mill in Lancasterroad, to convert into a lighting station. The site, which is central, contains about 3,000 square yards, and it is proposed to erect the plant necessary to supply light to the town of Preston, and the present temporary arrangements now at work in Corporation-street will be entirely done away with. The new station will be fitted with six 250-h.p. boilers, and coupled direct to six 200-h.p. engines will be the same number of 2,000-light slow-speed dynamos. The wires now erected overhead in the streets will shortly be taken down, and the mains will be placed underground. Light will be furnished to consumers night and day. A company (the National Electric Supply Company) has been formed for this purpose, with a capital of £100,000 in £5 shares, with 100 founders' shares. The present issue is £60,000. The board will include several local gentlemen. The present installation supplies 2,200 lights with a revenue of £1,320. The company anticipate, judging by orders in hand, a demand of 6,000 lamps at once, and the Corporation has already decided to enter into a contract to light Fishergate. Telephones in Austria.-Negotiations have been concluded between the Austrian Ministry of Commerce and the Telephone Company of Austria, for the transfer to the State at the end of next year of all the telephone lines at present worked by the company. The company have telephone exchanges in the towns of Prag, Trieste, Graz, Lemberg, Bielitz-Biala, Czernowitz, Pilsen, and Reichenberg. The concessions granted to the company for the first three of these have just expired; that for Lemberg expires in July, 1892, and others in March, 1893. The concessions gave the privileges of selling the plant or of taking it away on expiry. The negotiations just concluded extend the first concessions to the end of 1892, and reduce the others to the same time. The Austrian Government, by payment of an agreed amount, will then take over the whole business. The last balancesheet of the company showed the gross profits to be £18,513, or, after paying all expenses, £7,857, of which £4,418 were paid as dividends on preference and debenture shares. The working expenses were £7,131, and taxes and royalties paid amounted to £3,520. The number of subscribers on March 31, 1891, was 3,023, and the calls averaged 97,000 per week. The purchase-money to be paid, we are informed by the secretary, is to be £85,000.

Halifax.-At the meeting of the Halifax Town Council last week the minutes of the Gas Works Committee, which were agreed to in their entirety, contained a resolution that the town clerk should be instructed to apply to the Local Government Board for sanction to borrow £60,000 for present and future extensions of the gas works; also to apply to the Board of Trade for a provisional order authorising the Council to supply electricity for public and private purposes within the borough. With respect to the latter item the Mayor said the present electric lighting company supplied electricity from their premises in The Square. The capacity of these premises had reached their limits, and the company had no accommodation for further extension. The Corporation had the power at any time to take over the plant and works of the company and pay them out, and to establish works of their own. Under these circumstances the company had suggested that the present time was a favourable one for the Corporation taking over the establishment. They had obtained a report from Mr. J. H. Woodward, of the Electric Corporation, Limited, and he recommended the premises owned by the Corporation in Stead-street as a central station. It would, of course, be

some twelve months before anything could be done in the matter, but before any step was taken the matter would be fully discussed by the Council. The minutes were passed. The complete report was given last week.

Electric Crane Working.-At the time of their installation, we were pleased to give an account of electric cranes erected on a wharf in the City-road, London, by Mr. W. D. Sandwell, engineer to the Victor Engineering Works, Victor-road, Holloway. With reference to these cranes, the following facts and figures as to economy of working deserve especial notice. There were on the wharf a 10-ton steam crane, a two-ton steam crane, and two 30cwt. hand cranes. The cost of coal for driving the two steam cranes only was £250 per year (nearly £5 a week), steam having to be kept up night and day. All four of these cranes were fitted with electric gear, and a dynamo was put down, with all necessary wiring, switches, and safety fittings, the total cost being £300. A gas engine used for chaff cutting drives the dynamo, and the cost of the gas for the whole of the work-cranes, chaff-cutter, and corn-crusher, besides an ordinary friction hoist-has only been £56 for the year, a little over £1 a week, while the amount of the work done has been considerably in excess of any previous year. The engine is a 12-h.p. Crossley's Otto gas engine. A considerable reduction on fire insurance premiums is obtained at the same time, in some cases as much as 50 per cent. The cost of repairs and renewals for the year has been £5. 3s. It may be taken that the cost of fitting an ordinary 30cwt. crane with electric gearing is about £60, including everything but the engine. The future for the application of electric motors for the driving of cranes seems from these figures to be extremely promising, and Mr. Sandwell is to be congratulated on the results.

Gulcher Electric Light Company.-During the last six months the business of the Gulcher Company has made very important progress. We understand that Mr. de Castro, their chairman and managing director, who has been making a long visit to New Zealand, has succeeded in largely extending the business of the company in that colony. The street lighting installation at Wellington, which has been working most satisfactorily for some three years, is now to be extended to include the supply of about 3,000 lamps to private consumers. Bills have also been passed through the New Zealand Parliament for the lighting of Christchurch, and other important towns will follow in the immediate future. The general installation work of the company in New Zealand is also largely increasing. In the meantime an important order for a central station with plant for a first instalment of about 2,600 incandescent and 60 arc lamps has been secured, and will very shortly be in operation for lighting part of the city of Genoa. A branch establishment of the Gulcher Company has been inaugurated in this city, and a number of subsidiary orders have been already secured by the company in Italy. In London, also, the company are busy with installations of more or less importance, including the lighting of the People's Palace at Mile End-road, and a large contract recently secured for the lighting of "Modern Venice" at Olympia, West Kensington, are also in hand. The company have lately opened a showroom and offices, 139, QueenVictoria-street, and altogether we are glad to hear that their business during the last 10 or 12 months has made rapid progress, and that the company is now in a more flourishing condition than it has ever previously been in. The large installations at the Spanish, French, and German Exhibitions, which they have so well carried out at Earl's Court, coupled with energetic management, have doubtless conduced in some measure to this result.

ON THE RELATION OF THE AIR GAP AND THE

SHAPE OF THE POLES TO THE PERFORMANCE OF DYNAMO-ELECTRIC MACHINERY.*

BY HARRIS J. RYAN.

The object of this paper is not to deal with the subject in a new light, but to add to its literature a limited amount of data, the deductions from which go to establish the correctness of the ideas, and the utility of the suggestions put forth in the papers read by Messrs. Swinburne and Esson, at the meeting of the Institution of Electrical Engineers, on February 13 and 20, 1890. Up to the time of the publication of these papers the air gap was usually treated by contributors to electrical literature as an evil in

on the armature, except those that lie between the double angle of lead G E are acting with the field ampere-turns, while those between G E are opposed to the same. Therefore, by this route, the total number of ampere-turns actually aiding the field ampere turns is the total number of armature ampere turns, minus twice the number of ampere-turns that lie between the double angle of lead. By the route O, K, L, O, the number of ampere-turns acting is the number of ampere-turns on the field, minus the number of ampere-turns that lie between the double

n

FIG. 3.

FIG. 1.

a dynamo, having a necessary existence, and the smaller that it could conveniently be made the better. The shape of the poles had often been spoken of as having a somewhat decided effect on the performance of the dynamo, while but little had been said regarding the cause of such an effect.

There exists some difference of opinion as to what should be known as the number of ampere-turns on an armature.

angle of lead. We can then estimate with ample practical accuracy the magnetic density in the air gap at all points for any given total amount of magnetisation through the armature. The ampere-turns that lie between the double angle of lead are opposed to the action of the field ampereturns at all points. It is evident that the portion of the armature ampere-turns not included between the double angle of lead will increase the magnetisation through the air gap by the route O, M, N, O, just as much as they

O

FIG. 2.

For our present purpose we will assume that the armature ampere-turns equal

The number of conductors

FIG. 6.

on the surface of the arma- X armature conductors

ture

Number of poles.

Referring to Fig. 1, it is evident that, when we consider the magnetic forces acting in a working dynamo by the route Ổ, I, J, O, the entire number of ampere-turns on the armature are directly opposed in action to the ampere-turns on the field. By the route O, M, N, O, all the ampere-turns

* Paper read before the American Institute of Electrical Engineers, New York, September 22, 1891.

then that the magnetic resistance increases by the route 0, M, N, O, and the magnetic density by this route is no longer increased by the same amount that it is diminished along the route O, I, J, O. On the other hand, when the pole corners are fashioned, as seen in Figs. 4 and 6, so that saturation in the strengthened pole corners cannot occur in practice, the current in the armature can produce no modification of the total amount of magnetisation through it other than that which is produced by the action of the ampere-turns that lie between the double angle of lead

This action can always be compensated for by putting an equivalent number of series ampere-turns on the field acting with the field ampere-turns. The double angle of lead can be determined with sufficient accuracy, for with pole corners slightly extended at the centre (see Fig. 11) the diameter of commutation at all loads is very near the weakened pole corners. The pole corners are slightly extended at the centre, so that the coils always enter the field of the weakened pole corners gradually. The E.M.F. developed in the coils as they pass under the poles can never be far

length of air gap. In general it is found best to avoid heating in the armature core, as far as consistent, by the use of comparatively low magnetic densities for wrought iron. The magnetic resistance of the armature core, under these circumstances, is very small and may be neglected. The magnetic resistance between the pole faces is occasionally provided for largely, either through a saturated core of a ring armature, saturated lugs on armatures where the wires are placed in grooves, or both. This, in addition to what air gap may be necessary from a mechanical point of view, go to make up the total amount of magnetic resistance that is provided between the pole faces. Machines of this order have been developed largely through the old and rather expensive method of experimentation. This method has given us some types in which ordinary results are arrived at through rather extraordinary means. Take the case of a machine with a ring armature, wires wound in

different from that actually needed to reverse the current in the coil when passing under the brush. In this way the point of commutation in a dynamo can be kept the same when carbon brushes are used without undue sparking, as long as the armature does not reverse the magnetisation under the weakened pole corners.

From the discussion of the magnetic relations of an armature to its field in a dynamo, in connection with Fig. 1, it is seen that the magnetisation in the air gap under the weakened pole corners becomes zero, when the armature ampere-turns are equal to the ampere-turns on the field, whose magnetising force is impressed between its pole faces through the armature. This impressed magnetising force is that due to the difference between the total number of ampere-turns on the field and the number of ampere-turns required to set up the magnetisation through the field cores, from pole face to pole face. In order to commutate the current without spark at the commutator the magnetisation in the air gap under the weakened pole corners dare never be allowed to become zero. It follows, then, that the

FIG. 9.

grooves, a very small air gap, and poles shaped somewhat as shown in Fig. 2. Such a machine, operated as a dynamo, may require only a quarter of the number of ampere-turns that it will have on the armature at full load for field excitation in order to produce a certain E.M.F. at a given speed. Yet this machine produces a fairly constant potential at the brushes under all variation of load, and without undue sparking at the commutator, in the following manner: For the production of a constant E.M.F. at constant speed the total magnetisation through the armature must remain constant. At no load, one-fourth of the ampere-turns needed on the field at full load are provided by a shunt winding. This shunt winding is sufficient to set up the total amount of magnetisation for the production of the normal E.M.F. of the machine when there is no current in the armature. Now, in order to take the normal current from the armature without reversing the magnetisation under the weakened pole corners, three times as many

FIG. 8.

field ampere-turns, impressing a magnetising force between the pole faces, must always be somewhat in excess of the maximum number of ampere-turns on the armature. The amount of this excess need only be sufficient to ensure a positive field at A and B, Fig. 1, strong enough to reverse the current in the coils as they are commutated. When a certain amount of magnetisation is to be set up through an armature, with the application of the magnetising force of given number of ampere-turns impressed between the pole faces, we must provide the requisite amount of magnetic resistance between these pole faces. The value of this resist ance will have to be such that the impressed field magnetis ing force will establish the desired amount of magnetisation. This resistance in most cases is best provided for in a proper

FIG. 10.

series ampere-turns as there are shunt ampere-turns must be added to the field. The addition of these series ampere-turns must not increase the total amount of magnetisation through the armature, which is accomplished by the thin pole corners. The strong pole corners become saturated when the armature is furnishing even a small amount of the normal current for which it is designed. For most values of the current, then, the armature ampereturns tend to diminish the magnetisation under the weakened pole corners, but cannot increase it corre spondingly under the saturated pole corners. The action of the series ampere-turns on the field prevents the reduction of the magnetisation under the weakened pole corners to zero, while the saturated portion of the pole-pieces