insulating material. The latter is composed of ingredients which in a plastic state form a homogeneous mass which is readily moulded under pressure. The finished product is strong, durable, and non-absorbent, and is impervious to water and weather. It is especially adapted, either by itself or in combination with metal or other parts, for use in trolley wire hangers, span or guard wire insulators, arc lamp hangers, etc. Various illustrations are given of different insulators, single and double curve pull-offs, strain insulators, heavy terminals, trolley wire ears, the "Boston" trolley pole and wheel, and trolleys, etc. Among other appliances dealt with are the "Ajax" lightning arrester, wire-stretching machines, track drills, bond-bending machines, etc. We understand that these appliances have received the highest approval of practical tramway constructors and operators.

Post Office and the Telephone.-The PostmasterGeneral's annual report on the Post Office, issued on Wednesday, states that as regards telephones, the Telegraph Act, 1892, authorises the loan of £1,000,000 sterling for the purchase of the trunk lines of the companies, and for the construction of a Government system to connect the business centres of the kingdom. The negotiations have been carried on with the companies for the purpose of arriving at an understanding as to the areas within which their operations are to be conducted. The Department has proceeded with the erection of trunk lines between Leeds and Hull, London and Brighton, Swansea and Cardiff, Cardiff and Newport, Newcastle and Hexham, Newcastle and Morpeth, and Glasgow and Belfast. The trunk line between Glasgow and Belfast was opened for traffic in May. A main trunk line is at present under construction from London to Glasgow, passing through Nottingham, Sheffield, and Leeds. Branch lines will be erected from Nottingham to Derby and Leicester, and from Leeds to Manchester and Liverpool. The entire system will consist of metallic circuits, and when completed will enable each of the towns to communicate direct with London, or with each other.

The Tramway Congress.-The Congress on Tramways at Pesth, and to which reference was made in our last issue, was well attended, and no less than 60 delegates from foreign countries (including representatives from Germany, France, Belgium, Italy, Switzerland, Denmark, Sweden, Norway, and other countries) were present. M. Michelet, of Brussels, the president of the congress, mentioned that the tramway system of Budapest was already in an advanced condition, there being four different systems in active operation. These are the ordinary tramways; the electric tramway, which runs through the greater portion of the city; the cog-wheel railway, which goes up the hill at Buda; and the light railways connecting the city with the outlying districts. All these systems were inspected by the members of the congress, and the general opinion was that the Pesth and Buda trams are model lines in point of construction, working, and of cheap fares. The congress, which closed on Saturday, passed a resolution declaring that electric motive power for street railways, where a continuous current is used, had proved well worthy of recommendation, but that its applicability in the case of either new lines or old must for the present largely depend on the facilities offered by municipal or State authorities, as the financial results of street electric railways had not always been satisfactory.

Of

of telegraphic communication with lighthouses and lightships was discussed, and it was understood that a supplementary estimate would be taken for that purpose. The supplementary estimate was for £10,000, which, it appeared, was proposed to be added to the grant towards the Mercantile Marine Fund. course, that might be only a matter of form, but he hoped it was not to be taken as an indication that the Government considered the cost of the telegraphic communication ought in any case to be a charge upon the Mercantile Marine Fund. That was not his intention, and he hoped it would not be done, except, of course, where the communication was desired for Board of Trade purposes. Sir J. Hibbert said the supplementary estimate was put in the form in which it now appeared for convenience of discussion. The £10,000 would be kept entirely separate from the Mercantile Marine Fund. Sir M. HicksBeach said it had really nothing whatever to do with that fund. Mr. Mundella admitted that that was so. The fund would not bear one farthing of the expense of the telegraphic communication. The Board of Trade intended to execute the work by degrees, and the Treasury would supply the money, for which the Board would account.

Lighting of the City.-The electrical illumination of the City will soon be in full operation. The public arc lighting of the main thoroughfares is finished, and there only remain a a few street lamps for which positions have not yet been assigned. The current is supplied from the central station of the City of London Electric Light Company, at Bankside. The buildings here will on completion in the near future form one of the largest and bestequipped stations in existence. In the early part of the summer the length of ways laid by the company was 427 miles; cables drawn in, high tension 60 miles, and low tension 35 miles; and by the end of the year it is hoped the citizens will be supplied with 130,000 8-c.p. lamps. By using two circuits in a street the risk of a thoroughfare being thrown into sudden darkness by the extinction of the lamps through an accidental failure of current is obviated, as the failure of lamps on one side would not affect those on the other. The members of the Commission of Sewers recently decided to press for a reduction in the charge made by telephone companies-namely, from £20 to £8. This resolution was in due course transmitted to the directors of the City of London Electric Lighting Company, who forwarded it on to the telephone company with the request that the application should be considered. It is believed that from 80,000 to 100,000 8-c.p. lamps will soon be in working order, the current being brought into the City at a pressure of 2,200 volts to the transformer stations. These transformer stations are placed in areas (into which, for the purposes of lighting, the City is divided), and the current is delivered from these stations at a pressure of about 100 volts. The City of London Electric Lighting Company has experienced great difficulty in securing sites for these stations, which number 22. At the present time there are over 50,000 lamps connected up, and the end of the year will see the completion of the network of supply. Between £600,000 and £700,000 has been spent by the company in the work already accomplished, upon which some 500 men are now engaged, and as many as 1,000 were employed in the early part of the operations whilst the conduits were being laid in the main thoroughfares.

The Government and Telephony.-It is satisfactory to note that the telephone question is to receive proper attention, and that the agreement between the Government and the National Telephone Company is to be placed on the table of the House of Commons before it is ratifie

Mr. A. Morley on the 8th inst., in reply to questions put by Sir J. Fergusson, Mr. Hozier, Mr. Stuart, and Mr. Saunders, said that there appeared to be some doubt as to what was intended by the report of the Committee on the Telegraph Bill of 1892. He was informed that some members of the committee understood by the words used that the agreement should be laid on the table before final ratification, while the right hon. gentleman the late Postmaster-General and the right hon. gentleman the late Chancellor of the Exchequer, both of whom served on the committee, and the latter of whom was its chairman, understood and intended the words which were used to mean that Parliament should be informed of the terms of the agreement after it was concluded. His right hon. friend was aware that the proposed agreement was intended to carry out the policy for which he became responsible, and, indeed, would be the document embodying in legal form the heads of agreement which he settled with the company, and which were signed by him on behalf of the late Government before he left office. Under these circum stances, and as he (the speaker) understood, he suggested that the document should be laid on the table of the House before its final conclusion, and considering the difference of opinion which appeared to exist as to what was intended by the report of the committee, he had decided to take the course suggested, and to lay the proposed agreement on the table before it is signed. The draft of the agreement was now under the consideration of the company. He was advised that it was in strict accordance with the heads of agreement, which were signed by his predecessor, and with the report of the select committee, as well as with the Treasury minute which was laid before Parliament. It in no way limited or affected the discretion of the PostmasterGeneral to grant licenses for telephone exchange business. It did not extend the term of the license of the National Company. It restricted the operations of the company to specified areas, and withdrew from them the right to establish and work trunk wires between those areas. But it conferred on the company the right to exercise the powers which were conferred on the Postmaster-General himself by the Telegraph Acts of 1863 and 1878, and by the provisions in the Telegraph Act, 1892, relating to provisional orders. But this right was subjected in every case to the veto of the local authorities specified in Section 5 of the Telegraph Act of last session. Sir J. Fergusson asked whether power was given to take up streets without the consent of the local authorities. Mr.

A. Morley replied in the negative, and said that it was subject to the veto of the local authorities. On Monday, Sir R. Temple asked the Postmaster-General whether there would be any conditions in the proposed agreement between the National Telephone Company and the Post Office which would in any way limit the power of corporations, county councils, and other local authorities to impose any conditions they may think fit as to charges or otherwise on the National Telephone Company as a condition of permitting them to continue their telephone service, or obtaining further local privileges and powers-underground or otherwise. Mr. A. Morley answered in the negative. The matter was regulated by statute, and he would refer the hon. baronet to Section 5 of the Telegraph Act of last year. He promised to lay the agreement on the table before it was ratified.

Mechanical and Electrical Oscillations.—Mr. N. Tesla lectured on this subject at the recent Electrical Congress in Chicago. In relating his introductory work in oscillations, according to the Electrical World, he spoke of the experiments made with a plate in a magnetic field, the plate slowly and withdrawing it rapidly, and

vice versa, and actually producing rotation of the plate by oscillating the field, etc. Owing to the difficulties attending the use of high-frequency dynamos with a rotating armature of great speed, he desired to get a machine which would imitate the process of the Leyden jar by mechanical means and produce an oscillation of any frequency desired. The plan was to produce very rapid mechanical oscillation of small amplitude and vibrate either the armature wires in the magnetic field or the iron in the field and armature coils. The oscillator constructed for this purpose consists essentially of a very short cylinder with piston and valves, and a spring to resist the motion of the piston-rod. The piston is operated by compressed air at 60lb. per square inch. The valves are adjusted to produce a powerful cushioning effect in the cylinder at each stroke; or, as in the latest form of machine, to regulate the exhaust. The compression reaches as much as 16 tons, and the weight of piston and plunger is about 20lb. The ports on the largest of his oscillators were about the same size as in a 15 h.p. steam-engine. The period of vibration depends upon the resonance of the chamber and spring, and thus is not affected by a change in the air pressure. A simple analogy is the case of a musical string or bell-their tone does not depend upon the force with which they are struck; also with a pendulum the period is independent of the force applied in starting it. This enables oscillations of absolutely constant frequency to be obtained, thus producing currents of perfect vibration unaffected by air pressure, E.M.F., or any other condition, which discovery Mr. Tesla believes to be of the greatest importance. An interesting experiment was performed by attaching to one of these oscillating pistons a circular magnet with the poles on the top in. apart; a copper disc placed between the poles was rotated, due to the oscillating field and the retardation of the lines of force. Three different types of machines were shown for producing high-frequency alternating currents. In the first, which had a horizontal shaft, the armature consisted of a cylindrical iron core around which the wires were wound perpendicular to the shaft, and the field was a simple bipolar electromagnet; the oscillator was at one end of the shaft, which, with the core, vibrated longitudinally, and therefore the armature wires were oscillated across the field with an amplitude of about a quarter of an inch. In the second, also with horizontal shaft, there were two armatures and two fields, with the oscillator in the middle; the armatures each consisted of two flat, rectangular coils without iron, and were oscillated between the poles, which were in this case very close together. In the third, the field and generating coils were wound on flat screws of equal size and placed over each other, and the joint iron core of both armature and magnets was oscillated in their centre, the shaft being vertical. The outer or field coils were supplied with a constant current. The inner or generating coils were connected in series with the condenser. Mr. Tesla stated that he hopes to perfect these very soon and would use them as generators for his high-frequency currents, but the machines at present, though imperfect, were both light and fairly efficient for the power developed. The only experiment shown with this latest form of "high-frequency dynamo" was the operation of a small synchronising motor with closed-coil armature, the success of which was greeted by a burst of applause. Mr. Tesla, in closing, alluded to the great possibilities that were in store for these high-frequency generators. Currents of any period whatever could be supplied by the central stations, and synchronising motors operated thereby. The period would be so absolutely constant that clocks could be run with perfect regularity by means of it.

STATION, L. E. S. CO.

In the usual inflated style there appeared in Wednesday's papers an item of news headed" Shocking Accident at Blackfriars," with details to the effect that fatal injuries had resulted to one of the men engaged in the electric light station there, another being very seriously burnt and otherwise hurt. There is no need to minimise the facts; indeed, they ought to be noted very exactly, in order to show the importance of care in such work as this on the part of the men. If a plumber breaks into a gas-main, by the light of a tallow candle, the only satisfaction he usually gets for being blown up is to be called a fool for his wanton carelessness. The position in the present instance of the man in charge at the Blackfriars station was very similar, although, sad to relate, the poor fellow has lost his life under melancholy circumstances. As our readers will remember, the London Electric Supply Company have erected several sub-stations at different points of their circuits, where converters are provided for reducing the current pressure from 10,000 volts, at which it leaves Deptford, to 2,400 volts, the latter being again reduced to 100 volts by the converters on consumers' premises.

The annexed plan-for which we are indebted to Mr. P. W. D'Alton, the company's engineer-will show clearly the arrangement of converters and switch gear at Blackfriars, where one of these sub-stations is placed. The 10,000-volt mains are not shown, but those carrying the secondary current at 2,400 volts (in connection with which the accident happened) are represented by dotted lines according as they are below or above ground. At A, B, C, and D are four plug switches, by means of which the load may be transferred from one row of converters to the other, or both may be kept in circuit if desired.

and

It appears that on Tuesday night, after changing over from one set to the other-that is, from the set on the right hand of the plan to that on the left-the main switch in the primary circuit of the unused converters being of course thrown out-the unfortunate man who now lies dead at Guy's Hospital, and who was in charge of the station, omitted to take out the plugs at B and A, as he should have done in accordance with the rules of the company. The consequence was, of course, that the secondaries of the right-hand side converters were in circuit with those on the opposite side which were carrying the load; and the assistant who had been detailed to clean and dust the converters and fuses no sooner happened to touch the frame of a converter with one hand whilst dusting with the other, than he at once received the full force of a 2,400-volt shock.

On seeing him in this condition the deceased man immediately rushed forward and tried to pull him away, but himself received a severe shock, and was thrown back violently upon his head, and it seems at present as though his death were due more to the effects of the fall than to the electric shock, inasmuch as he could hardly have taken the full force of the current through the assistant's body.

thick indiarubber soles, and were, therefore, as much as possible insulated from the ground. The assistant is now in the hospital suffering from severe burns and shock to the system; but it is hoped will make a good recovery. This unfortunate accident was clearly due to the fault of the deceased man himself, in not carrying out the rules laid down for his guidance; had the plug switches been a procedure gone through removed in the usual waytime and again by the man himself-no danger whatever would have been incurred. He had been in

the employ of the company for six years, and was a man of fine physique. The assistant is a young man, 20 years old, only engaged a year or 15 months ago. Although, of course, there will be statements made as to the company being at fault, it seems quite evident that in this dent resembles very much those which sometimes occur on case no possible blame can be attached to them; the acciour railways, when an engine-driver forgets his position and runs past a danger signal to his own destruction. It is, however, none the less regrettable from every point of view.

ELECTRIC LIGHT AND POWER.

BY ARTHUR F. GUY, ASSOC.MEM. INST. ELECTRICAL ENGINEERS. (All rights reserved.)

DISTRIBUTION OF ELECTRIC POWER.

(Continued from page 223.)

LOW-PRESSURE SYSTEM.

In order to equalise the pressure over a network of distributing mains as much as possible, and to enable a farther distance to be supplied without any increase of the fall of pressure in these mains, the method of trunk mains was adopted, these trunk mains being used solely and simply for conveying the current to several determined centres in the network. No branch wires are tapped off these trunk mains, and no lamps are run off them, so that they serve as "feeders," and are known by that name. It is evident that the more "feeders" there are, the more will the pressure be equalised over the system, because there will be more central points, at all of which the pressure will be maintained constant and the same. At the end of each pair of "feeders"that is, at each "feeding centre "a thin pair of "pilot" wires are taken back to the dynamos, so as to indicate what the pressure is at the centre. As a practical illustration, we may take that 112 volts is the pressure that must be maintained constant at the feeding centres, and at full load; this may mean, say, 118 volts at the terminals of the dynamos: for the nearer centres a little less, for the farther centres a little more, when all the centres have different distances. As the current flowing in each feeder increases or decreases, so a greater or less pressure will be required at the dynamo terminals in order to always maintain the 112 volts pressure at the feeding centre. Taking as six volts the total fall of pressure along the feeder at full load, there will only be required 115 volts at the dynamo when the load in that feeder is reduced to one-half. By adding a number of "feeders" to the simple parallel system, the radius distance of the supply mains can be increased to double, treble, or even more. The greater the length of feeders supplied, and the more feeding centres there are in the network of mains, the more equalised will be the pressure.

No low-pressure systems of distribution are carried out without employing feeders in a judicious manner, and as they are solely for the purpose of giving better regulation to the supply mains, the money sunk in them becomes an additional expense. It is found that in a well-designed distribution system the money spent on feeders should be between 30 per cent. and 50 per cent. of the money spent on the distributing mains, according to the nature of the area to be supplied.

Fig. 26 gives an idea of the way feeders are used. Where A, B, C, D, E, F are the six feeding centres, and f the "feeders," the distributing mains denoted by m, radiate out from each centre, and those nearest each other

are joined together, and so make a circuit round the source; only the positive wires are shown, to make the diagram clearer. Of course the position of the centres and their number and proximity to each other are determined by the nature and extent of the district, and the diagram given is merely to show how they are employed, it being almost impossible to get a district where the distributing mains and feeding centres can be arranged perfectly symmetrically, as in the case of Fig. 26. If the current that is flowing is reduced to one-half of its value, whilst at the same time the pressure is doubled, we still have the same electrical power; and generally the current can be reduced by as many times as the pressure is increased without altering the value of the product which represents the power generated. We showed that a main cable of lin. diameter and 500 yards long had a resistance of about 016 of an ohm, and that with a current of 500 amperes flowing through, the fall of pressure throughout its length was eight volts, so that if the pressure at the generating end of the cable be 100 volts the fall is then 8 per cent. But suppose we work our lamps with a current of only half that value, 250 amperes, and at a pressure of 200 volts, the power is the same; but instead of our lamps being fixed in simple parallel they must now be arranged in parallel rows of two in series-that is, two lamps in series must now be placed across the positive and negative mains so as to absorb the 200 volts-because the lamps are only made for 100 volts pressure. The same current passes through the

there is no current flowing in it. Fig. 27 shows the connections of the three wires.

The dynamo is wound for a constant pressure of 200 volts, and the pressure can be regulated by a rheostat in the shunt coils, for compensation for fall in the circuit. The third wire, signified by N, is placed between the positive and negative wires, but does not return to the dynamo. Service mains for 100 volts can be taken off either + and N or N and -, because the + is at 200 volts pressure and at 0. Of course the circuit can only be completed when there are lamps on both pairs of mains, as the lamps of one pair are in series with the lamps of the other pair.

FIG. 27.

Fig. 26 shows four tappings of service mains, two being taken from + and N, and two from N and -. By having this neutral wire, N, should one lamp go out the others will not be thrown out of circuit, whereas if the lamps were fixed two in series straight across + and -, then one of the pair going out would make its fellow go out.

Since there is a current flowing through the neutral wire only when there is an inequality of load, it is usual in practice to make its sectional area not much more than one-half what either of the other two may be ; in some cases it is made only one third. There is, therefore, a great saving of copper in the three-wire system as compared with

A

FIG. 26.

two lamps that are in series, so that the total current used is obtained by multiplying this current by one-half of the number of lamps in use. In the simple parallel arrangement, the total current is obtained by multiplying the current through the one lamp by the number of lamps there are. From this, we see that for the same number of lamps we only require one-half the current when the pressure is doubled. If our current is now 250 amperes, the sectional area of the cable can be reduced correspondingly, and this will give us the same current density, the resistance is doubled, and so we have the same fall of pressure-namely, eight volts; but the working pressure is now 200 volts, and so we obtain a fall of only 4 per cent. instead of 8 per cent., as with 100 volts.

Reckoning in the negative cable as well, there is a total fall of pressure of 16 volts in both cases, but on the 100-volt circuit each lamp received only 100-16=84 volts, whereas, on the 200-volt circuit each lamp receives (200-16)÷292 volts. Therefore, keeping the percentage of loss constant-that is, the loss for each 100-volt lamp-doubling the pressure will allow the current to be carried double the distance, or

Distance is proportional to Pressure.

The above fact furnishes us at once with a means for extending the distributing area of a system. The threewire system of distribution enables us to use 200 volts, the third wire being called the "neutral wire," because when there is a balance of load of each side of it-that is, when there are as many lamps burning between the positive and neutral wire as between the negative and neutral wire

the two-wire system. Allowing a two-wire system to have cables of iin. diameter, the total sectional area of copper employed is 1.5708 square inches.

With the three-wire system, we have first the sectional area of the two mains,+ and -, reduced to one-half, because one-half of the current is used; but at 200 volts, the percentage of fall of pressure for equal distances is only one-half, so that to bring it up to the same as the two-wire system, we can double the current density, and this can be