telephonic or telegraphic communication to the lifeboat stations. He says he intends to move a resolution in Parliament next session, as follows: " That, with a view to the better prevention of loss of life and property in cases of shipwreck, and to give speedy information to lifeboat authorities and rocket apparatus stations, in the opinion of this House it is desirable that telephonic and telegraphic communication should be provided by Government between all the coast guard stations and signal stations on the coast of the United Kingdom, and on such parts of the coast where there are no coast guard stations, the postal telegraph offices nearest to the lifeboat stations." He adds that it has been estimated that an expenditure of £100,000 would be sufficient to establish such a system-a mere bagatelle when the vast importance of the object is considered.

Catalogue. We have received a copy of their catalogue from Messrs. S. Z. de Ferranti and Co., Limited, of Charterhouse-square, London, containing particulars and illustrations of this firm's well-known dynamos and mains. Some very capital woodcuts show one of these Ferranti alternators, with exciting dynamos mounted on the same axle, and fitted for rope gearing. These machines are made for any tension-from 1,000 to 3,000 volts for ordinary station work, to supply from 1,500 to 30,000 10-c.p. 35-watt lamps. The alternations of current in these machines are 5,000 cycles per minute, or 10,000 phases. They are rated to have exceptional margin of safety, and have frequently been run at various stations at 50 per cent. over normal output. Alternators for coupling direct to high-speed engines are constructed for 4,000 complete alternations, 350 or 400 revolutions. Complete installations of sub-station transformers, house transformers, station switches, and synchronising gear are shown, together with fuses, and the celebrated Ferranti mains, which we fully illustrate elsewhere.

Electric Illuminations at Worcester.-The festivities in connection with the return of the Earl and Countess of Dudley to Worcester last Saturday after their marriage, was made the occasion of an effective electric lighting display at the Worcester Cathedral. One of the Naval Exhibition search-lights was placed on the roof, together with four arc lamps in positions at other points between the pinnacles. The prominent position of the cathedral made the operation of the search-light very effective. The work was undertaken by the British Electric Installation Contractors, of London and Worcester, under the superintendence of Mr. Morgan Williams, their consulting engineer; and the staff of Mr. Ronald Scott, of Acton, carried out the erection of the plant, which consisted of a powerful portable engine driving two dynamos, the whole being placed in a portion of the enclosure at the back of the cathedral. Elsewhere in the town accumulators were used for arc lighting outside a tradesman's shop, this work being also carried out by the same company, under Mr. Oswald Swete, acting engineer to the local electric company.

Christiania.—Tenders in all from 20 different firms were received for the Christiania electric lighting station, of which 13 were for the whole installation and the others for special parts. For the whole installation tenders were received from the Edison General Electric Company, New York; Crompton and Co., London; Siemens Bros., London; Electric Construction Company, Wolverhampton; Siemens and Halske, Berlin; Schuckert and Co., Nürnberg; Thomson-Houston International Electric Company, Hamburg; Helios Company, Cologne; Continental Edison Company, Paris; O. L. Kummer and Co., Dresden; Sharp and Kent, Westminster; Woodhouse and Rawson, Limited, London; Chrom-Accumulator Company, Berlin. For the boilers only, the firms: Düsseldorf-Ratingen Company,

Ratingen; Babcock and Wilcox, New York; Gohrig and Leuchs, Darmstadt; L. and C. Steinmüller, Gummersbach. For the mains only: Callender's Bitumen Company, London. For the steam engines only: J. and A. Jenssen and Dahl, Christiania. For the dynamos and fittings only: Mather and Platt, Manchester. The contracts are to be awarded within six weeks from October 10.

Bournemouth Telephone.—The burnt-out telephone exchange at Bournemouth has been again temporarily started, to the great satisfaction of the subscribers, who have been living telephonically in silence for over a week. Mr. Mackenzie Williams, district superintendent of the Western Counties Telephone Company, and a staff of skilled workmen, were at work almost day and night repairing the damage and endeavouring to arrange for a temporary installation. The large switchboard that was damaged has to be replaced by one from Chicago, and in the meantime a smaller board, consisting of three single-line switches of 100 subscribers each, has been fixed, awaiting the arrival of the multiple board from the States. On Tuesday morning the temporary installation was complete, and three of the operators at once began to ring up the subscribers. The present communication is only temporary, but the regular exchange will be ready in a few weeks. It speaks highly for the company that within so short a time they should have restored order out of the chaos which reigned a fortnight ago, and given their subscribers as soon as possible the benefit of using the telephone in the meantime.

Fowler-Waring Cables.-The Fowler-Waring Cable Company, 32, Victoria-street, and North Woolwich, send us their new illustrated catalogue. The cables are of two classes, "lead-covered" and "lead-foiled." The former are sheathed in solid drawn lead, and are for use in underground conduits, factories, public works, and steamships, or wherever great strength is requisite. The latter are sheathed in a light covering of lead, and outwardly protected by a fibrous braiding. The cables are all covered by means of special machinery for lead covering, and are free from pores and cracks. The insulation is very high, ranging from 1,000 to 5,000 megohms at 75deg. F., and all cables are tested after prolonged immersion with high-pressure currents. Tables of sizes and prices are clearly given, not only for the special cables, but also for flexibles and circular braided cords for pulleys. Jointing materials and tools are illustrated, and also the various methods of jointing. The lead joints are specially described with very full particulars and cuts. Aerial cables are separately dealt with, and the hooks and suspending wires shown. Tables of sizes, specific gravities, melting points, and relative conductivities of various metals complete a very useful catalogue.

Lighthouses.—The question as to whether the authorities have done altogether wisely in substituting the electric light for oil in lighthouses is one which is agitating minds in the marine world. There seems to be in some quarters a decided view to the contrary, and petitions, as has been reported, have been presented to Trinity House upon the subject by shipmasters who find that the absence of penetrating power in fog is a serious disadvantage, the light being least useful when most required. A lighthouse is not required to light the way of a ship, but to afford a fixed point or landmark for guidance. The penetrating power is therefore more important than mere strength of light. The question is being further taken up by French naval engineers. It would certainly seem that with the enormous surplus of lighting power we get in the electric arc that means are not impossible for converting or lowering a portion of this merely illuminating power into pene

The problem of how to secure sufficient insulation, combined with the difficulty of manufacturing and laying heavy concentric mains at this enormous pressure, was one that seemed to offer insuperable difficulties, and when, in addition to this, Mr. Ferranti resolved to manufacture the mains in short lengths of 20ft., necessitating an immense number of joints, scepticism as to the result was rampant, and it is safe to say that no living electrical engineer beside himself would have dared to propose or attempt to carry

2,500 volts, a step which was regarded as an immense jump at a period when any pressure over 100 volts was rare. Having demonstrated that with suitable precautions there was no greater danger resulting from the use of such pressures than with, say, 50lb. of steam in a boiler, the second jump from 2,500 to 10,000 volts, though daring, was in reality by no means as much so as that from 100 to 2,500 volts, for the same precautions, with added insulation, proved sufficient. It is interesting to remember, however,

that a pressure of 10,000 volts will give a spark between terminals of in. or so in air, and on a damp day sparks with the sound of a pistol-shot will jump over an inch or more of insulating surface. It was to conduct a large current at this pressure, and to secure permanently good results, that the Ferranti mains had to accomplish.

After many and exhaustive experiments the insulating bodies which were finally selected were paper and black ozokerite, or earth wax. It will be interesting here to give Mr. Ferranti's ideas upon the subject of insulation of hightension mains, a subject to which he has naturally given more than ordinary attention.

The necessary points to consider are two: durability of substance and the factor of safety. No one can definitely tell how the insulation may change in course of time, but what can be at once tested is the factor of safety of such insulation. No fault will develop in the insulation unless the dielectric is sufficiently strained to produce enough mechanical effect to cause a gradual change; in other words, unless it is strained beyond the limit of elasticity. To take an example in mechanical engineering, a connectingrod, for instance, the metal may be strained to any point within its limit of elasticity, and nothing gives way; strain it outside this limit and it may go at any time-in a week, a day, an hour, according to the overstrain. Its strength will depend upon the margin of safety. It is the same with insulation. Strained below the limit, the insulation will not give way; strained above its limit, the breakage is but a question of time. The Ferranti mains are made with a very large margin of safety, a margin that has been accurately determined by direct experiment. From these experiments it is found that a thickness of in. of paper saturated with the black wax, is pierced within one hour by 20,000 volts-some specimens will go within ten minutes, and nearly all within the hour: above that thickness the insulation is not pierced. This being so, with the present mains, which have in. of insulation, there is eight times that thickness, and with half the number of volts we have 16 as the factor of safety. In the Ferranti mains there are 60 layers of waxed paper wrapped one above the other, and the factor of safety is so large, even if one or two layers were partially faulty, it may be trusted to the remainder to give perfect safety. In point of fact, no failures of tested mains have yet been experienced by reason of direct failure of the insulation. Fifteen faults in all were experienced in the 30 miles already laid, mostly of want of continuity. Only two faults were found with 20,000 volts on the whole run, both of these due to water in the joint at the time of making. Mains constructed for only 2,500 volts have been tested for months with 25,000 volts without giving way, and it is on a series of practical experiments such as these that Mr. Ferranti is relying for the safety of his larger mains. There is, we may say, a gradual mechanical change if the insulation is too thin. There is no change at all if the insulation is sufficiently thick. The pressures in the present form of mains have been doubled and trebled, running up to 28,000 volts to try and break down the insulation, but they have been unable to do this, and so feel perfectly happy with their 10,000 volts.

Nothing but time, of course, can prove the question of durability of the insulation, but the materials have been chosen as the most durable it is possible to find. The wax used for insulating is the very same black wax as that in which the mummies were boiled to preserve them in old Egyptian times. The oldest mummy in the British Muscum was found wrapped in linen and boiled in this same black wax. The chemically pure paper used is hermetically sealed down from the air by the tube which is drawn tightly over it. Paper, again, is one of the most permanent substances known. There is a papyrus book in existence known to have existed 3,000 years. Two of the most permanent materials in the world have therefore been used in the Ferranti insulation. It is not maintained that these mains will last 3,000 years, or 1,000, but Mr. Ferranti does consider that the chances are so enormously in their favour that they are commercially good enough for our day.

With regard to the jointing, this is a most important part of the whole system. The mains are constructed ready

for laying in the ground; the weight is heavy and the length is kept to 20ft., so that a few men can handle them. In the 30 miles of mains there are therefore seven or eight thousand joints. To allow this the joint must be absolutely safe when once properly made. This indeed is what renders the whole scheme practicable. To make such a joint in the insulation was an achievement long doubted, but is now proved perfectly possible. The desiderata were a very long jointing surface and perfect contact. These were achieved by making a long slanting cone-like surface, the protruding point of one main fitting into the hollow of the next, these surfaces being accurately and truly turned and polished to gauge, and then heated and forced together by hydraulic pressure, by which means the insulation becomes practically one solid piece.

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Having said so much as to the principle of the Ferranti mains, we will briefly again describe the manufacture for the purpose of completing this series of articles. Tubes of high conductivity copper are taken, cut into 20ft. lengths, and straightened. The usual size of tube to carry up to 250 amperes is of in. section, and the size in. inside diameter, and 18in. Outside diameter. Lengths, 20ft. long, of brown paper are cut off from a roll 3ft. wide, and a length of this paper is glued by its edge to to the copper tube. Meanwhile, other rolls of paper are passed over long iron plates heated below by open fires, and thus thoroughly dried; these are passed through a bath of hot melted black mineral wax, drawn over rollers and through the air for some distance until dry; they are then cut into 20ft. sheets and placed for use on shelves. The copper tube has squared pieces of wood knocked into its ends, and is then placed in sockets of a slowly-revolving roller on a table which has at the back a set of rollers, a bath of hot wax, and revolving gear. As the tube revolves, lengths of the prepared paper are inserted between it and the brown paper, sheet after sheet, until 60 sheets are served in. During this time heavy rollers come down upon the tube, compressing the paper, and at the same time by displacement boxes dipping into the bath, the wax is made to flow up and saturate the sheets. When the required thickness is served the wax is made to flow back, the insulation compressed still more upon the copper tube, and a tape is wound spirally over the whole. The tube covered with its insulation is then removed, the wooden pieces knocked out, and the whole slipped into a second tube of copper. This tube is of the same total cross-section as the first-viz., in.-but being larger in diameter is proportionately thinner. The size of this tube is 12in. inner diameter, and 11ğin. outer diameter. The tube is left a little larger, so as to slip easily over the inner tube with its insulation, and is then passed through a die and drawn down upon the insulation. This outer tube is now served with the insulation in the same manner as the inner tube : first a length of brown paper glued by one edge, then several sheets of waxed paper to the thickness of in., compressed and taped as before. The whole is slipped into an outer iron tube to act as a protecting shield. Melted wax is forced by a pump through a small hole in the centre beneath this iron casing till the inner space is completely filled. The whole is then sawn off at the ends into exact 20ft. lengths. The section of the main is shown in Fig. 1.

The next process is the preparation of the joint. One end of each length is formed into a projecting cone, and the other end into a hollow cone, by means of a special hollow spindle lathe. The length is placed on this lathe, the outer iron shield is removed for a distance of 17in. from the end; 14in. of the outer insulation, E, thus exposed is then turned up, leaving bare that length of the outer copper conductor, B; 6in. of this conductor is now removed, and the insulating material between the two tubes is turned carefully down, forming a cone at the end of the cable, as shown in the illustration, Fig. 2. The interior of the inner tube is then slightly enlarged by drilling for a length of 6in. inside.

The length of main is then reversed, and the insulation, C, of the other end is coned out for a distance of 6in. to exactly the same taper, while the iron shield is removed for a length of 11in., and the outer insulation for a length of Sin., leaving the outer conductor exposed for this length.

The mains are now ready for laying. Each length is