separately tested to 20,000 volts, the ends are capped to prevent dirt getting in, and are then sent out to the place required. They are jointed together on the spot, as follows (see Fig. 3): A tight-fitting copper rod, a, 12in. long, is driven into the inner tube, A, of the hollow coned end. A tight-fitting sleeve of copper, F, is driven for a distance of 8in. on the outer conductor of the main to which it is to be jointed, and this sleeve firmly gripped on by means of a special tool by three or more circular corrugations, as shown. The two cones are then inserted one within the other, the surfaces being previously warmed, and are forced together and driven home by screw clamps, a total pressure of about three tons being employed, and when still under compression the copper sleeve is firmly locked to the other outer conductor by means of circular corrugations as before described. The sleeve, F, and the outer insulation, E, are wrapped at the junction with insulating material until they become of the same external diameter as the iron tube, D, when an iron sleeve, G, 30in. long, is passed over the joint and corrugated down at both ends. In order to fill up any air space in the outer insulation, hot wax is forced in through the boss, H, of the sleeve, G, the whole being finally closed with a gas plug. The laying of concentric mains is thus relatively a very simple matter; they are supplied ready for jointing together, and may be carted out and laid as gas-pipes are, no cement channels or specially-prepared conduits being necessary. It is usual, however, in crowded streets to lay them in a wooden trough, with wooden separating slips, the trough being filled in with pitch with an upper layer of concrete for extra protection. They may be laid under any pavement or roadway, causing a minimum of disturbance and occupying a minimum of space. As will be seen, they adapt themselves readily to laying through tunnels and subways, in which case they may rest on wall brackets. When laid in this manner they are subject to variations of temperature, to compensate for which all that is necessary is to give them at certain points a slight wave in laying. To bend a main to go round a corner an ordinary rail bender, as used on railways, is employed; a curve of 6ft. radius being made in this way with but little trouble. In bending, it is found there is no appreciable drag between the layers of insulation and conductors. For making branch connections a special T-joint is employed; this consists mainly of a cast-iron box with suitably designed base and cover arranged to fit watertight. These joints do not, of course, appear on the road surface, being inserted in the run of the mains as required. The joint has three stuffing-boxes through which the ends of the mains are brought in. A screw bolt from the centre of the branch main connects to the inner conductor of the main itself, and the joint is wrapped with paper insulation; the outer conductors are connected with a gunmetal bridgepiece of the shape shown, Fig. 4. Street boxes are also placed in the run of the mains at distances of about 200 yards. These are iron boxes similar in principle to the Tjoint boxes, but are placed in small brick chambers, having removable covers flush with the road surface, Fig. 5. The interior is thus accessible for testing and other purposes, while the arrangement of the connections is such that the joint can be easily and quickly connected or disconnected. These joint and street boxes may be filled with rosin oil, by means of which very high insulation is insured at these points, and the full pressure of 10,000 volts may be safely used. While the above description applies more particularly to mains for parallel distribution, the system may be employed with equal advantage for series work. ductors, the current can only return direct to the machine, where the safety fuses prevent it doing any harm. The fuses employed are also illustrated herewith. The smaller one, Fig. 6, has a 12in. break, and is used in houses for the primary circuits of transformers. The larger fuse, Fig. 7, is identical with the first, except that it is adapted for main currents, and has a multiple fuse with a 24in. break. The plugs are arranged for separating the multiple fuse wires. The absence of necessity for channels or conduits in the Ferranti system is an item which should be taken into account, and has, further, the immense advantage of avoiding the possibility of explosions from an accumulation of sewer or lighting gas, which have occurred so frequently with both high and low tension systems throughout Europe and America. Explosions of this kind have already occurred in London. In fact, when a conduit or line of pipes is opened, the presence of gas (which is found, moreover, to impair the insulation of cables laid in that manner) is very frequently detected. Such methods are also liable, sooner or later, to dangers which arise when water is present. For instance, when bare conductors are used and water gets access to them, they are liable to be shortcircuited or injured by electrolysis. With insulated cables in pipes or conduits, the alternate presence and absence of water affects the insulation, damaging it in time, and when it is present in winter, it is liable to freeze-the ice crushing or piercing the insulation and causing partial or total short-circuitings. This occurred in London during the late winter of 1890-91. With regard to safety the following experiments were carried out : In the presence of representatives of the Board of Trade, the Post Office, and local authorities, a main which had been running continuously under a pressure of 10,000 volts was submitted to two engineers, who, with a cold chisel and sledge hammer, managed, after considerable time and much deliberate labour, to cut through from the outer to the inner conductor while 200 h.p. at that tension was being transmitted through it. They did not feel the slightest shock, although they were standing on a large metal plate making earth. A similar trial has been made with a pickaxe. The mains have also been submitted to a lengthened test, after laying, with 30,000 volts, and have given no trouble. It has thus been forcibly demonstrated that this system of conductors offers every possible guarantee of human safety. We have referred to the Ferranti mains more particu larly, perhaps, in connection with high-tension distribution, but it is apparent that they are also adapted for 100-volt or other low-tension distribution, or where a large mass of copper is required. By their construction the greatest amount of copper conductor is contained in the least space, the cables are buried direct without the use of conduits, and can be carried anywhere and under pavements where there is no room for conduits. The house connections are rapidly and cheaply made, perfect insulation is obtained, there is no fear of any short-circuiting from water, and no fear of explosions. For three-wire distribution the cable is manufactured with three concentric conductors instead of two, and is laid and jointed exactly as above described. We understand that arrangements are now made by Messrs. S. Z. de Ferranti and Co. with a large firm in the North of England for the manufacture of the Ferranti mains on a considerable scale, and large plant is being put down for this purpose. PULLS AND BELL-REPEATERS. With regard to the resistance of long lengths of these MAJOR BAGNOLD'S PATENT IMPROVED BELLmains, a length of 7 miles (i.e., 15 miles of lead and returu) between London and Deptford was tested by Dr. Fleming, and the actual resistance was found to be 2.20 ohms, while the calculated resistance of a length of copper of that section was 2.16 ohms, thus showing that the resistance of joints is inappreciable. The mains can be touched on the outside and handled with impunity when a current at the highest voltage is flowing, without the possibility of anyone receiving a shock, the metal covering being to earth and acting as a complete discharge shield. In the event of a fault occurring between the inner and outer con For over 40 years the familiar push-button used in conjunction with electric bells has remained unaltered except as regards the artistic design of its exterior, notwithstanding that considerable inconveniences are connected with the use of this simple household fitment. The ordinary pushbutton must be pressed in a direction at right angles to the surface of the wall or other support to which it is fixed. Again, the contact made is not always of the best ; it is essentially a "butt" contact, and possesses little or no self-cleaning powers. When definitely established, say, in the immediate neighbourhood of a bed, or of an office, or dinner-table, it is difficult to actuate these push-pieces from any other position. Pull-pieces have been devised, but these need to be pulled, as a rule, in one particular direction; flexible cord connections are also used, connected to "pear" pushes, but these again are seriously liable to derangement, and may be said to contain the elements of their own destruction. Generally speaking, there are K C other than in that of the axis of the rod, RR, will deflect that rod, and cause the shank of the knob to touch the ring, CC, and make the necessary contact. This contact needs no silvering or platinising, as the knob can at any time be given a circular motion, which will clean the contact surfaces and ensure the establishment of the circuit. If it be desired to actuate this contact-piece from a distance, it is only necessary to tie a fine cord round the horizontal groove on knob, K, and this cord can be led off in any required direction such as to a bed, a chair, or a dinnertable. This bell-pull, which is also shown in Fig. 2, is made in various patterns and sizes. It can also be conveniently combined with a sound repeater. When a bell-pull or push is actuated, it is of immense convenience to be able FIG. 1. R many instances of daily occurrence in which the shifting of a bed, of an invalid's chair, or of a writing-table necessitates the advent of the electric bell-hanger and the moving of the contact-piece from one position in the room to another. In order to obviate these inconveniences, Messrs. Siemens Bros. and Co. are now supplying, under license from Major Bagnold, a simple and effective arrangement of bell-pull which, no matter where fixed in a room, RIMBRULS FIG. 2. to know that the electric bell has rung. Figs. 3 and 4 show a new form of sound-repeater, which, combined with the contact previously described, makes a most convenient and efficient fitting for this purpose. In Fig. 3 the repeater is shown complete with the nickelled steel bell dome, and in Fig. 4 in Fig. 4 without the dome. When the latter is screwed on, one pole of the electromagnet is presented to the sound-boss of the bell; as soon as the contact is closed and the circuit is intermittently interrupted at the distant "chattering" bell the bell dome of the repeater is set into vibration, and gives out a clear ringing sound sufficient to indicate that the distant bell has acted, but not so loud to be inconvenient to the occupants of the room in which the contact is made. can be easily actuated from any point in that room by attaching a thin cord, and leading this cord away in the desired direction; a very slight pull on the cord is necessary to make contact and ring the bell. A diagram of the bell-pull and connections is shown in Fig. 1. An elastic rod of steel, RR, is set vertically with its lower end firmly fixed into a brass block, B; on its upper end is screwed a brass knob, K, the shank of which passes through a brass ring, CC; the conducting wires are attached to B and C. A slight pressure applied to K in almost any direction The above-described system of ringing a steel bell magnetically can be applied in other ways. Thus, supposing it is desired to actuate several bells in series on one circuit, one of these can be an ordinary "chattering" bell and the others can be simply "sound-repeaters" without contacts. No difficulty of adjustment is experienced as in the case when ordinary chattering-bells are joined in series. The special bell-pull and the repeater-bell are fully protected by patent, and Messrs. Siemens Bros. have been appointed sole manufacturers of the apparatus, SHIPLIGHTING PLANT. The accompanying illustration represents one of Messrs. Laurence, Scott, and Co.'s shiplighting plants, SL5 type. The output of the one illustrated is 65 volts, 140 amperes, at 260 revolutions per minute. The engine is well and substantially built, with very large bearing surfaces and ample lubricating arrangements, but otherwise calls for no special mention. The weight of the dynamo field magnets is taken through brass packing-pieces on two strong ribs that run across from one side to the other of the bed-plate, whilst they are held in position by means of the muntz metal studs coming through the strong brackets on the side of mutator of the above machine there are 110 sections, one turn of conductor to each section; but there are only 55 slots cut in the armature, each 355in. wide. This would be an excessive width, but in winding, each slot is made into two by means of three longitudinal strips of charcoal iron, running the whole depth and length of the slot, but insulated from both the conductor and the armature core. These strips reduce the width of each slot to 14in., and thus make the outside surface of the armature sufficiently even, magnetically, to entirely do away with the heating of the pole-pieces and noise that would have been caused by the wider slots. The armature of the machine is 13in. diameter outside, 11in. at the bottom of the slot, and 9in. long. It is wound with four parallels of No. 13 wire braided. The magnets call for no special mention. They the bed-plate, circular brass distance-pieces being arranged between these brackets and the magnet poles. A very rigid job is thus secured. The armature of the dynamo is of Laurence, Scott, and Co.'s usual type, the conductor being wound in slots milled into the plates which form the armature core. These plates have hexagon holes, into which the hexagon steel shaft is driven with insulatingpieces, so that the mechanical arrangement is exceedingly good, and the armature will stand an amount of rough usage and hard work that would be fatal to any other kind. It is absolutely necessary, if an armature of this kind is to be successful, that the opening between the projections and the periphery of the armature-i.e., practically the width of the slot should not exceed a certain amount. In practice, it is found it should not be more than twice the clearance between the armature and the pole-pieces. In the com are of Lowmoor iron, and have a sectional area of 85 square inches. The ampere-turns in the shunt are 9,370, and in the series 7,840. The plant illustrated was worked up to 200 amperes for six hours before leaving the maker's works. Even with this very excessive load there was no sparking, and the rise of temperature in the armature at the end of the test was only 80deg. F. The makers have recently obtained a license from Mr. Gisbert Kapp to use his patent end connections for strip armatures, and these will be used in all the large machines. They have been making a large number of shiplighters for Scotland and the North of England during the last 18 months. They have had an absolutely clean record with them, not a single breakdown having occurred up to date, and the buyers in every case have been thoroughly satisfied. THE ELECTRICAL ENGINEER. Published every Friday. Price Threepence; Post Free, Threepence Halfpenny. Governing the Choice of a Dynamo 451 Trade Notes-Electrical and 453 441 443 Mechanical 444 London County Council... .................. Correspondence Literature Electric Finchley Local Board..... 445 Companies' Meetings City Notes... 446 Provisional Patents, 1891 TO CORRESPONDENTS. .. 454 455 456 456 456 456 ELECTRIC TRAMWAYS. It is instructive, if not amusing, to notice the criticisms against any new departure. The great majority of those who write seem to imagine that the end of all writing is faultfinding. A few writers indeed find a reason for such fault finding. They contend that success is more likely to come if all faults are diligently sought out, in order that they may be remedied. No doubt there is something in such argument, but it is worth very little. The person who is doing the work knows more about the weak points than any casual critic can tell him, and usually knows also of weaker points which are more or less unknown to the critic. The introduction of railways was strenuously opposed, as was the introduction of gas, and as is the 455 introduction of electric light and traction. A good deal has been said against overhead wires for tramlines. Surely the better plan is not to censure indiscriminately, but to assist even the introduction of overhead lines in convenient places, so that we may acquire a practical knowledge of the disadvantages and of the advantages of such systems. Discussing quite recently the question of the fundamental financial knowledge required for the quicker development of electric tramways, Mr. Graff Baker contended that what all wanted was the actual working expenses free from what he termed general charges. The receipts of a tramway company are split up into three parts-one portion has to pay the working expenses, second has to meet the general charges, the third, or the balance, being profit, goes in dividends. We understand that in America the interest upon debentures is generally charged to working expenses, while in England it is usually the first charge upon profits. Of these three parts the first, or the working expenses, of any one system is pretty constant, the other two can in a paying concern be made to fluctuate considerably at the will of the directors. The item that fluctuates most in the working expenses is perhaps the coal bill. Thus, while the wages of car driver and conductor, of engineer, electrician, stoker, and labourer are pretty much the same at Leeds or Exeter, the cost of coal is not SO constant. It is only from actual experience that the actual cost of working a tram per car mile run be known. Unfortunately, the peculiar methods used in making balance-sheets of public com13s. Od. panies usually prevents any decisive answer being given as to cost per car mile run," otherwise in the course of a few months we should have here in England a sufficient knowledge of the subject to determine the problem. In order to see which is the best system, however, we must know more. Consider for a moment the three systems at present before us-(1) with overhead wires; (2) with batteries; (3) with underground conduits. The cost per car mile run on each of these three systems must be very different for them to be equally commercially successful. It is pretty certain that the initial or capital expenditure upon the first system Mr. would be least, and it is difficult to see how the supply electric light themselves; but the Local working expenses could be higher than in either of Government Board returned an answer that they the other systems, hence undoubtedly number one did not allow any gas company throughout England would be commercially more successful than either to have this power, because it was desired to of the others. It is important, therefore, to know place it in the hands of the councils. Having the cost of construction per mile. In another the power granted to them, he thought the column we give a paper read at the recent Street Council should reap the profit and not the comRailway Convention at Pittsburgh. The various pany. The water supply he instanced as necessimoney columns are in the American currency, but tating 200 or 300 per cent. advance in price from it will be easy for those who are discussing tramway that demanded years ago, and asked the Council to work in England to translate the various amounts go into committee and consider the agreement clause into English currency. Given that the conditions by clause. Alderman Mount said that they had in America are greatly different from those ruling given the matter careful consideration, and had here, we contend that this is the is the kind of selected the Brush Company as the best. analytic statement it is desired to obtain from Mills also thought the arrangement was most English practice in order to be able to satisfactory, and would be sorry to see the Council fully understand themselves the possibilities of electric provide electricity according to traction. Figures of this kind form an admirable the present business habits they might be argument in reply to the "bird-in-the-hand" theory bankrupt in three years. It was further we referred to last week. We agree, then, so far, stated that the cost of lighting Canterbury would with the contention of Mr. Graff Baker, that an be £2,700 against £1,600, the present cost of gas; accurate knowledge of the working expenses should but it did not appear that any binding clause was form the best lever to induce capitalists to find the included for public supply, nor to deal with the capital necessary for the change. At some future continuance if the company were not a success. time it may be necessary to discuss the question of Eventually it was decided that the terms for public general charges, but in the meantime we ask those lighting should be arranged, and that a draft agreewho have charge of electric tramways whether they ment should be asked for, a copy to be supplied cannot, without disadvantage to the concerns which to each member of the Council, and that in a they control, from time to time publish authoritative fortnight a committee meeting of the whole Council analyses of working expenses for the benefit of those be held to settle the matter. who are still watching and waiting. CANTERBURY. as a A protracted discussion took place at the Canterbury Town Council last week upon the electric lighting question. The Electric Lighting Committee reported that, having consulted with the Brush Electrical Engineering Company, they recommended that the Canterbury electric lighting order be transferred to that company on the following terms: That the company pay costs of obtaining the order, to be not over £350; that the Corporation have the right to take over the works at the end of twenty-one or thirty-one years going concern, including a valuation for goodwill; that no other order be granted within the borough; and that the agreement be subject to the formation of a local company, with a nominal capital of £50,000, to which the proposed agreement be transferred, the Brush Company paying all costs of such transfer. These were the heads of the agreement. Alderman Mount, as chairman of the Council, moved the confirmation of the report. He considered they had made very good terms with the company, and did not think it necessary to call in other experts. The company would have to compete with the gas, and would in their own interest supply it at as low a price as possible. Alderman Hart, one of the directors of the gas company, mentioned that he was a party a little while ago to an application for power to CORRESPONDENCE. One man's word is no man's word 11 Justice needs that both be heard.' ALTERNATING-CURRENT ELECTRIC RAILWAYS. SIR, I read the short note on the above in a recent issue of your paper with much of that gratified chagrin which one feels on finding that another is on the track of one's pet idea. For some time past I have been of settled opinion that direct-current systems are practically out of the field of commercial application for all tramway and open roadway work unless overhead conductors can be difficulty of securing any real insulation to a long length of employed. The immense, and in fact unsurmountable conductor lying continuously or intermittently bare in an open conduit, or to the surface contacts of closed-conduit systems, burdens all such schemes with a fatal and fundamental drawback. And though the objections against overhead conductors are perhaps more prejudiced than real, the feeling against them in this country is apparently too strong to permit of their general adoption here; so consideration the too expensive and bulky accumulators, that for electric traction in our streets, leaving out of the we are forced to the least favourable expedient, so long as we confine ourselves to the use of direct currents. But once conceive the use of alternating currents for this purpose, and it is surprising how simple the problem apparently becomes. I say apparently advisedly, because it has yet to be seen what purely practical difficulties may arise. Yet being well rid of the two great bogies of bare mechanical collection, a pleasing variety of solutions offer and practically uninsulatable cables or surface contacts and themselves, and true varieties, not mere vagaries and plagiarisms of the same thing. To mention a few we have, besides the method of simple induction from primary in the roadway to secondary on the car, a scheme based upon the repulsion motor principle of Elihu Thomson, and another upon the principle of con |