currents can be produced without any difficulty. The next question is the generating station for a large installation. The generator will be an alternating-current dynamo of as low tension as possible. The winding of the armatures of the dynamos used in the Oerlikon Works installation consists of copper bars, 30 millimetres thick, which are insulated by merely being placed in paper tubes. It is, perhaps, surprising that the winding of a dynamo can consist of such thick, massive copper bars, but their use is even possible if the bars rest in closed holes in the armature iron. This method, it will be remembered, was already employed by the author in 1885, in his ordinary continuouscurrent dynamos. Such machines, with a tension of about 40 volts, are absolutely safe. The current from a dynamo of this type is then converted by means of an oil-filled transformer into a high-tension current. As regards the measuring and safety appliances at the station, all switching and measuring can be done with the low-tension current, by which no greater danger is incurred than obtains with ordinary continuous low-tension current installations. At the most, for the control of the high-tension current a static voltmeter may be employed, and which does not require to be touched. To prevent short-circuitings, leaden cut-outs are placed in either the high-tension or low-pressure leads. For the transmission of the current over long distances and open country overhead conductors are required. There is much prejudice against this, but time and experience will overcome it. As regards insulating the wires at the places of support, the ordinary double-bell telegraph wire insula tors are fairly efficient in a dry atmosphere, but are unsatisfactory when there is moisture. Here oil is again required, and for this purpose the well-known Johnson and Phillips fluid insulators, which the author describes, first originated. The insulating properties of these simple insulators is exceptionally high. Prof. H. F. Weber, of Zurich, made experiments in the autumn of 1887 with those insulators which had been in use for a year and a half on the Krieg stetten-Solothurn line. The total length of wire is 15 miles, and with a current of about 2,000 volts pressure not the slightest loss due to the insulation could be detected. The insulation of the conductors was absolutely perfect. However, for currents of 10 times the voltage in question, more is desirable. The most simple way of increasing the insulating effect is to use two of the fluid insulators to support a third, and other methods have been devised by the author. These fluid insulators require from time to time to be inspected, cleaned, and refilled with oil. This is not a disadvantage, but is, on the contrary, a recommendation. It necessitates an involuntary control of the fastening of the wires to the insulators, of the poles, and of other protective arrangements, which might otherwise be neglected. Having now got a satisfactory solution of the question of the insulators, the next point is the poles. Wooden poles will be most often employed, and as it is desirable to have as few as possible, they must be strong and placed at distances of from 230ft. to 330ft. apart. If iron poles are used, the distance can be increased to 660ft., but a correspondingly stronger conductor will be required. Under all circumstances, the poles must be as high as possible, and the conductors carried above everything, including telephone and telegraph wires. Where the conductors pass over streets or railways, a protective net or wires are needed between the poles so as to catch the conductor in case of breakage. These protective arrangements must have a good earth connection. Where the conductors cross others, it is advisable to attach them all to a pole. found generally that it will not be reconverted into mechanical power alone. As a rule, it will probably be employed for various purposes in connection with the driving of motors, for electric lighting and otherwise. In any case the high-tension current will not be used direct. In most cases the current will be transformed downwards not only once, but twice. For instance, a current of 30,000 volts will be converted at transformer stations, which will be equivalent to central stations, to 1,000 or 2,000 volts and then distributed to the consumers or to sub-transformer stations. The whole arrangement from the generating station to the place where the current is utilised may appear at first sight to be roundabout and uneconomical, but closer inspection shows a totally opposite result. As regards the generating station the dynamos for low-tension currents can be made considerably cheaper than those for high-tension currents, so that there are only the transformers to be taken into consideration. The efficiency of low-pressure dynamos is also higher than that of high-tension machines, so that the difference of the combination of dynamo and transformer only comes to from 1 to 2 per cent. at the utmost. By the employment of high-tension currents for the transmis sion, the amount of material for conductors and the great reduction in the loss in the same, more than counterbalance the extra cost of the transformers and the loss in the transformation. The following is a simple example of this: In the case of transmitting 500 h.p. over a distance of about 12 miles, the currents can be generated at an E.M.F. of 5,000 volts with a loss of 10 per cent. in the conductors, whilst in another case it can be converted to 30,000 volts by means of transformers and carried at a loss in conductors of only 3 per cent. In the first plan conductors of about 90 square millimetres section would be required, and in the second of only nine square millimetres. In the former the weight of copper would be 32 tons roughly, and in the latter only 3.2 tons. The copper required is thus only one-tenth, although the tension of 5,000 volts already represents a fairly high pressure. By means of such economy in the material of the conductors, the very large increased cost in the transformers would be counterbalanced. Taking the subject from the point of view of efficiency, the following results are obtained: The efficiency of a 500-h.p. machine at 5,000 volts will be at most 92 per cent. Allowing for a loss of 10 per cent. in the conductors, the efficiency at the other end of the line is about 83 per cent. This is is about 83 per cent. In the second case the efficiency of the primary dynamo and transformer is 90 per cent., the efficiency of the conductors 97 per cent., and the same in that of the secondary transformers. The ultimate efficiency is thus 84 per cent. In the latter instance the 84 per cent. is available at a handy E.M.F., while in the former the tension is about 4,500 volts, which, under certain circumstances, is very inconvenient, and has consequently to be transformed. It is evident, therefore, that the second plan, notwithstanding the double conversion, is the more economical. Protection against lightning must be provided. This safeguard must not only be provided at each end of the conductors, but also at intervals along the line. The distance apart which the lightning conductors should be cannot be accurately determined as yet, and must be found out by experiment and by experience. A question about which little definite can be asserted is the loss of current through the atmosphere. Whether this plays a part at certain tensions over long distances we shall perhaps discover some months hence. In any case, the danger of any appreciable loss in this manner is much less than has hitherto been believed in technical circles. Coming now to the question of the utilisation of the current which has been generated and conducted, it will be The idea of transforming low-tension currents into high ones at one end, and re-transforming them into low-tension currents at the other, is not a new one. The author drew up a project on these lines, at the commencement of 1886, for the town of Naples, where he proposed to transmit current at 10,000 volts. Nothing, however, was done in the matter. In view of the Lauffen-Frankfort transmission scheme, the author made some preliminary tests. He employed two small transformers of about 5,000 watts for a tension of about 30,000 volts. These were connected together by a copper conductor, carried on more than 100 fluid insulators, and in the secondary current of the second a corresponding number of glow lamps were inserted. The primary current was supplied by a small alternating-current dynamo at 100 volts, which was driven by an electro-motor. This instal lation has been running almost daily since the middle of November, and partly under most unfavourable conditions of weather, at tensions up to 40,000 volts. There were no abnormal appearances during this period, either in the transformers or in the conductors. The transmission of electric power by means of currents of, for instance, 30,000 volts will enable its distribution over very great distances, and enable sources of power at present lying idle to be utilised to the advantage of industry. The carrying out of such installations is quite practicable, but there is still much to learn and to improve. PUBLIC LIGHTING IN EASTERN EUROPE. The French Government having desired its consuls in the principal towns of the East of Europe to report on the public lighting of those places, the representatives of France have furnished particulars on that subject, which are published in the Moniteur Officiel du Commerce for July 9 and 16. According to these reports it appears that there exists no manufactory of lighting apparatus in Roumania, with the exception of one recently founded in Bucharest, and this at present does no more than produce wickholders for petroleum lamps; the cylindrical glasses for the same are principally made at the glass works of Azuga. It is intended to make lamps in the Bucharest factory, and before very long it is probable that the whole apparatus for lighting with petroleum will be manufactured at least at one place in Roumania. With the exception of certain small accessories, everything connected with lighting by means of gas has to be imported into Roumania from abroad. Most of the lamps now used in that country are furnished by makers in Austria-Hungary, mainly from Vienna and from Buda-Pesth. Lamps are also imported, but in much smaller quantities, from Germany. There is no gas used in any town of Roumania except Bucharest. Everywhere else simple petroleum lamps are used, and the town of Galatz is lighted by 1,695 of these. At Jassy the theatre and the circus have lamps of vegetable oil, but everywhere else petroleum only is used in glass lamps with a straight wick. For domestic lighting, lamps of all dimensions are used, with burners and circular wicks, all of which lamps are imported from Austria or Germany. When we turn to Servia, we find that Belgrade, the capital, contains no manufacturer of illuminating apparatus. The streets are lighted by a few petroleum lamps with reflectors, and when the municipality has need of a supply of lanterns it applies to the Jewish tinmen, who produce what is required. Nisch is lighted only by petroleum lamps at certain important points of the town, and there is not even a shop devoted to lighting or lamps; the latter are ordered from Vienna or Buda-Pesth, and sold by grocers or dealers in hardware. In Sofia, the capital of Bulgaria, there are several dealers in lighting apparatus, but there is no manufacturer of these articles in any part of Bulgaria. What is used comes exclusively from abroad, and principally from Bohemia. There is a small importation of glass lamps from Belgium. No other substance than petroleum is used in any part of the country. Lighting apparatus only figures in the Bulgarian trade reports under the head of "Glass manufactures." The figures of the import value of these articles, in 1889, was £5,400. In Varna, as in Sofia, petroleum alone is used for lighting. The favourite form of lamp is a cheap suspended lamp, with a single burner. There is a great sale at Varna of small lamps, specially introduced for the little towns and villages of the interior. These are made of glass, and cost about 18s. a hundred. In European Turkey little is used except petroleum. Even in the public offices of Constantinople, into which gas had been introduced, it has been found so bad and so expensive that it has for the greater part been rejected, and petroleum once more taken into use. In private houses, as in shops, cafés, and restaurants, nothing is now used but the large petroleum lamps. The electric light is employed only in the palace of Yildiz, it being forbidden by law to use it elsewhere. The supply of lamps for Constantinople is almost entirely in the hands of Austrian and German merchants. The kinds which they supply are usually of second-rate or even inferior quality, cheapness being an essential matter. The natives are in the habit of calling petroleum gas, even when they are speaking French, but it is important to understand that they always mean petroleum. There are three French shops in Pera, and an Austrian house in Stamboul, where lamps of a better quality may be bought. At Adrianople no gas is manufactured, and an attempt. which was lately made to illuminate the city with the electric light was a complete failure. The only material used is petroleum, which is imported from the Russian establishments at Batoum. The city is lighted by very cheap lamps on a most imperfect system, consisting merely of a cylindrical box of tin-plate, scarcely eight centimetres high, and priced at from 8d. to 9d. each. The inside of certain establishments, such as cafés and hotels, is lighted by lamps of a more elaborate description, from Austria or Germany. Austria inundates the country with a cheap article, devoid of all solidity of construction, but sufficient to satisfy the requirements of the Turks. The only product employed for lighting purposes in the island of Crete, except candles, is Russian petroleum oil of very bad quality, and dispersing a disgusting odour. The lamps are generally very common, but cheap. Most of them possess a glass reservoir mounted on a stand in porcelain or metal. These are imported from Austria. No manufacturer of lighting apparatus exists in Eastern Roumelia. Petroleum lamps are used, and these can only be purchased in the capital, Philippopolis. At Bourgas, the chief port of Roumelia, all lighting apparatus has to be brought from Constantinople. Oil is but very little used for lighting in Salonica, and, consequently, there is no sale for articles intended for this species of illumination. Gas works have recently been set up in Salonica, but hitherto the number of consumers is very small. Petroleum is almost exclusively used throughout the town, and there is a considerable market for apparatus used in this kind of lighting-portable lamps of all sorts, with glass, porcelain, etc. All these articles are of Austrian manufacture, and of inferior quality, but find a ready sale, on account of their cheapness. A Paris house attempted, some time ago, to introduce in Salonica lamps of its manufacture, but they were not bought, as they were too expensive. A manufacturer who wishes to sell his lamps in this town ought first of all to obtain information as to the price at which similar articles are at present sold there. The only form of illumination which is employed in Albania is petroleum lamps, the inportation of which reaches a value of £500 or £600 a year. None are manufactured in the country-even at Janina, Scutari, or Durazzo, but are manufactured in Austria and introduced from Trieste to ports along the Albanian coast, and sold in the bazaars. the bazaars. In Bosnia-Herzegovina, also, gas and oil are totally unknown as illuminants, and the whole country depends on the importation of cheap petroleum lamps from Austria. In Greece gas is used in the towns of Athens and Corfu. In the former everything connected with lighting by gas is supplied by a French company on the spot; in Corfu the apparatus has to be imported from an English gas company at Malta. In the rest of the country lighting is almost exclusively performed by means of petroleum lamps of Austrian or German munufacture. At Syra there exists no person who regularly sells lighting apparatus of any description, but very bad porcelain or metal lamps may sometimes be picked up at the china or tin shops. There was once a proposal that Syra should be lighted with the electric light, but the poverty of the municipality and political reasons combined to prevent it. Mr. T. B. Sandwith, her Majesty's consul-general at Odessa, writing to the Foreign Office, under date of 1st August, says that the port of Odessa, in contradistinction to the town of that name, having, for many years, remained unlit, even by oil lamps, and, within two years only, being lit by gas, has at length been illuminated by electricty. An installation has been completed, at a cost of 80,000 roubles (£8,400). This consists of 64 arc lamps, of 2,000 c.p. each, and of two lanterns, one at each end of the breakwater, which runs the whole length of the port. The illuminating power is generated by two of Wilson's vertical engines, of 67 h.p. each. The Odessa Town Council has just assigned a sum of 20,000 roubles (£2,100) annually for the working expenses. The new installation is a great boon to the shipping interest, the whole of the port being brilliantly lighted up, so as to admit of the loading and discharging of steamers by night.-Board of Trade Journal. THE ELECTRICAL ENGINEER. Published every Friday. Price Threepence; Post Free, Threepence Halfpenny. WILLIAM STURGEON. Prof. S. P. Thompson is indefatigable in tracing out the history of electrical science, and in the attempt to give due credit to those who have added to our knowledge of the subject. He is enamoured of the work and position of William Sturgeon, and, it may be remembered by those present, made some very complimentary remarks as to Sturgeon's posi tion in the history of the subject at the Society of Arts during his last Cantor lectures. Within the TO CORRESPONDENTS. last few days Prof. Thompson has issued a small pamphlet for private circulation only-entitled All Rights Reserved. Secretaries and Managers of Companies "William Sturgeon, the Electrician; a Biographical are invited to furnish notice of Meetings, Issue of New Shares, Installations, Contracts, and any information Note by S. P. T." This pamphlet has accidently connected with Electrical Engineering which may be come into hands-not from from the interesting to our readers. Inventors are informed that therefore we dare his anger in publicly attendany account of their inventions submitted to us willing to the matter. However, after all, Prof. our author, Thompson desires publicity in that one of the objects he has at heart in connection with Sturgeon is to find the whereabouts of "a portrait of Sturgeon, a fine oil painting, which was formerly in the possession of his adopted daughter, Mrs. Brierley." This portrait" is believed still to exist," but where is a question not easily answered. At any rate, Prof. Thompson has as yet been unable to find it. This search, as many another, has come a little late. Mrs. Brierley, according to the tombstone in Prestwich churchyard, died on January 19, 1884—not so many years since. Surely, then, given due publicity, there must be still living many friends of Mrs. Brierley who, visiting at her house, would remember if in her later years the portrait was in the house. The pamphlet does not tell us if Luke Brierley, the husband, died before or after his wife, or is still alive. If dead there should be some near relations who could tell how the furniture was dispersed, and one of whom may have possession of the muchlooked-for portrait. It may perhaps be regarded as a bit of sentimentalism to trouble about the looks of a dead and gone electrician, but surely in a sense such a man as Sturgeon has done more good for mankind at large than some of the political men whose names are recorded in every child's history and whose portraits hang in the galleries of the homes of their descendants. The Marquis of Worcester might have been an idiot according to the views of his contemporaries for experimenting with steam, but those who developed the use of steam as a motive power have done more for their kind than the whole race of monarchs of any kingdom. If, then, Sturgeon was the discoverer of the electromagnet, he discovered a piece of apparatus that bids fair to create as great a revolution as did the discoverer of the capabilities of steam. A glance at Sturgeon's published utterances shows how vast a progress has been made since his time, and should rather tend to modify the arrant conceit of those who do not hesitate to assert, practically, the infallibility of the authorities they worship or claim to be. Sturgeon, in 1843, says, "Various means have been resorted to for measuring the relative degrees of galvanic force; but as every attempt has failed, I have introduced," etc. We trust that Prof. Thompson's action will be the means of unearthing the lost portrait. It might be as well if those willing to make enquiries were told what has already been done. Has anything been found out about Luke Brierley or his family, or about the family of Ellen Coates (Mrs. Brierley)? Knowing what has been done might save someone the trouble of going over the same ground again. Might we also suggest at this time of credit-giving that Dr. P. M. Roget, the secretary of the Royal Society in the early thirties, has not received the amount of honour due to him for his then excellent treatise on electricity, galvanism, magnetism, and electromagnetism. On p. 54 of " Electromagnetism is an illustration and description of " a very powerful temporary magnet" (an electromagnet), but no reference to Sturgeon in connection therewith, though credit is given in other things to Sturgeon. The experiments of Prof. Mott are referred to on the same page, and these are described by Sturgeon in his " Researches," as is duly noted in Prof. Thompson's new work on "The Electromagnet." TELEPHONY. The discussion on telephony in London has been continued in the Times. Mr. F. Faithfull Begg, in a letter dated Sept. 16, offers some criticisms, but no information. Mr. Wallace, in one dated Sept. 17, does the same, and only one or two sentences of his letter need be referred to. He says: "No system will be adopted (that is, by the new company) until it has secured the approval of a commission of echnical experts. To them will be submitted Mr. Bennett's and any other system worthy of consideration." We should like to ask, Where are the men to form a commission of experts to sit upon suggestions of such men as Mr. Bennett, the Government officials, Mr. W. H. Preece, Mr. Heaviside, and Mr. Gavey? Why, there are no experts who can hold a candle to these men, any one of whom has more knowledge of the subject than any dozen men in the country, excepting perhaps one or two of the National Company's officials. Messrs. Preece, Heaviside, and Gavey are Government officials, and certainly will not be permitted to sit on a commission and give the result of their experience to further the plans of a private company. There are one or two men who have been, but are not now, connected with the National Company who are keen-sighted enough to know what is better than the system of the National, but no single person, except Mr. Bennett, as yet has contributed to this discussion who may, by the greatest stretch of the imagination, be termed a telephonic expert. It may be that these experts are to be brought from the Continent or from America, though what they can know about the peculiarities of English working remains to be seen. The Duke of Marlborough, with whom we understand Mr. Wallace is working in this matter, somewhat possibly to the surprise of his colleague, sketches out the plans it is proposed to adopt. His letter appears in the Times of Wednesday last, and is reprinted elsewhere. The Duke of Marlborough, however, falls into error in estimating the difficulties of good telephony at too low an estimate, and he will find when he comes to actual work that something besides twin wires is required to ensure satisfaction to his customers. Let him ask Mr. Fletcher, of the National, where his troubles begin and where they end, and if they would be ended by twin wires. We fancy Mr. Fletcher in reply would smile, and shake his head. There are other points in the Duke of Marlborough's letter to which exception might be taken; and if we might presume to advise, it would be that the financiers of the new undertaking, having obtained that cheap advertisement for their plans this discussion was intended to obtain, would retire into the background, carry on the work nature has given them talents for, and employ the best men available for organising the system to be adopted on the twinwire plan. It was perhaps necessary for those who intended to float a company, and ask the public for money, to take the course that has been taken, but they will only damage themselves by entering into technical details they evidently are only slightly familiar with. 66 WONDERFUL. Really, the writers in the daily papers must imagine electrical engineers as partaking of the nature of gnomes, burrowing underneath the surface of the earth and working in the dark. According to the reasoning of the Globe we require an invention for every application of electricity. We thought that something had long ago been done towards adapting the electric light to picture galleries, but it seems that it is not so, for quite recently a young firm registered a design of this nature (expressly for the illuminating of pictures), and already they have commissions to fit a couple of galleries with their patent reflector." We are glad to hear of this success, and might suggest the registration of a design for a reflector to illumine the various public clocks, and no doubt the act of registration would bring further orders. By the bye, is the registration of a design the same as taking a patent? Our contemporary evidently thinks so. We are further informed that "if the enterprise be successful, it may not be very long before the National Gallery becomes an agreeable, cool, and entertaining evening resort." There has been no time within the past ten years when the National or any other picture gallery could not have been successfully lighted electrically. It is nearly that time ago since we saw at least one private gallery so lighted, and we understand the light has been used continuously since it was installed without a failure. We should hardly like to hint that the lighting of such galleries electrically depended upon the designing of a reflector. There certainly has been no delay through lack of reflectors: the delay has been caused more from lack of money or inclination. It is very easy, also, to suggest the lighting of this and of that public building; but other considerations than the possibilities of such lighting have to be taken into account. There is the initial expenditure, the maintenance of the light, an extra expenditure in all directions from having the buildings open through longer hours. If the Globe will do its best to educate the Treasury and the House of Commons up to the point necessary to permit this extra expenditure, the electrical engineer will not be found lacking in suitable apparatus. So far as lighting is concerned, and to a great extent so far as the transmission of power is concerned, the only deficiency in carrying out any idea is money. LITERATURE. The Elements of Dynamic Electricity and Magnetism. By PHILIP ATKINSON, A.M. Crosby, Lockwood and Son. That part of the year which is usually called winter is approaching, though, perhaps, the climatic conditions may not materially differ from those persisting during the period called summer. However, the coming time is devoted more to books than the immediate past, and it will be necessary to refer to the accumulation upon our table. Dr. Atkinson has compiled a very readable manual of the usual pattern. He discourses in a simple way of the prominent phenomena and apparatus pertaining to the subject, and may be acknowledged to have fairly met the scheme design-viz., a book "for learners rather than for the learned It is perhaps lucky that Edison had not uttered his doubts of Ohm's law and mathematical conclusions before this work was written, or the author would have waited for the new Edisonian electrical manual that will save a world of labour and put us all right. Still, with all who stand afar off and admire authorities, this book will be welcome, as being clear in style, amply illustrated, and altogether according to "Cocker." One statement will be read with some astonishment, coming from America-viz., the crediting of Hughes (and we deem correctly) with the invention of the microphone. Dr. Atkinson must be commended for such boldness. Altogether the book is very readable and just what the general reader wants. An Introduction to the Mathematical Theory of Electricity and Magnetism. By W. T. A. EMTAGE, M.A. Clarendon Press, Oxford. This book is written purely from the scholastic point of view, and as such must be judged. It is hard to realise wherein the practical value of such a book lies. The examiner has to set questions, the student has to answer them in order to pass examinations. That is the fad of the era. When the student has satisfactorily answered the questions he is a learned man, though if a dynamo was sparking he might be unable to adjust the brushes. The aim of this class of book and the system it represents is to make the subject as difficult to the student as possible, and at the end of his student career to leave him with as little real knowledge as possible. Our American brothers, in their dry matter-of-fact way, laugh at the system in their little jokes. Thus, an intellectual-looking man, in goggles, happens to be in the country, and being of an enquiring mind, asks the man in the field a lot of questions. What is growing in that field? Turnips. And in that? Corn. Dear me! What is that animal? Oh that's a cow; and so on. In the end the man in the field enquires the profession of the questioner, and hears that he is the editor of an agricultural paper, and has been editor for 20 years. But we must be thankful for small mercies, and thank Providence that Oxford and Cambridge men have not yet put out brass plates or sounded brazen trumpets to proclaim that they practise as "consulting engineers." Having said thus much against a system, and expressed inability to agree with Pope, that "whatever is is right," we are bound to admit that, accepting the situation as it stands, the book before us is one of the best ever issued in the interests of that system. Given the necessary mathematical knowledge, the subject. To point the moral of our story, take as an the student is here presented with an excellent epitome of example the last paragraph in the book, relating to that most interesting topic of the hour-the transmission of power: "13. Transmission of Power.-Sometimes a dynamo is used at one station, where there is a source of energy; to develop a current and drive a motor at a distant station, where work is required to be done; by means of conducting wires between the two stations. This operation is generally called the 'transmission of power.' "Suppose we have a series dynamo and series motor. "Let E be the E.M.F. developed by the dynamo. "E' the back E.M.F. developed by the motor. "R the entire resistance of the circuit formed of dynamos, motor, and conductors. "I the current passing. "The electrical energy developed per second is E(E-E') EI= = R "The work done per second by the motor is "The work lost in heating conductors is "The intrinsic efficiency of the arrangement is E' Ε ́ E Suppose we increase E and E', keeping E- E' constant. Then the energy lost in heating conductors remains the same as before; but both the efficiency, E/E, and the activity (E- E')2/R, are increased. "Thus it is advantageous to run at high E.M.F.'s." This is all very pretty, but the student should consult a text-book to find out, say, the loss in the motor, the loss in the leads, the loss in the generator, and so on. He wants to know the power he must put into the motor to get a horse-power on the shaft of the motor; more, he wants to know the power he must put into the shaft of the generator in order to get under the given conditions a horse-power delivered at the shaft of the motor. What, again, we ask, is the practical value of a book professing to treat the subject in an advanced manner, that leaves us in ignorance of such questions? and we doubt if the most gifted reader would get more practical knowledge from this and similar works, than he would from a pocket-book crammed with formulæ. In fact, all the examination system provides us with in the way of books is of the character of a more or less elaborate way of developing formulæ. The Arithmetic of Electricity-A Manual of Electrical Calculations by Arithmetical Methods. By T. O'CONor Sloane, PH.D. New York: Henley and Co. London: E. and F. N. Spon. The title of this book pretty well explains it purport. The method is to state a rule and then work out an example. Thus 74 rules are given dealing with practical requirements. An example will be the best means of showing the value of the book. On page 96 is given : "Rule 71.-One volt E.M.F. is generated by the cutting of 108 (100,000,000) lines of force per second. Example.-A single convolution of wire is bent into the form of a rectangle 7 x 14 inches. It revolves 25 times a second in a field of 20,000 lines per square inch. What E.M.F. will it develop at its terminals? "Solution: The area of the rectangle is 7 x 14 = 98 square inches. Multiplying this by the lines of force in a square inch, we have 98 x 20,000 = 1,960,000. Each side of the rectangle cuts these lines twice in a revolution, and makes 25 revolutions in a second. This gives 25 × 2 × 1,960,000 = 98,000,000 lines cut per second, corresponding to 98 x 10 x 10-8-98 x 10-2 volts E.M.F. generated, as 00000006 1 98 volts." = 100 A series of 15 tables at the end adds to the value of this little book. 100 |
