cation of electricity as a universal motive power was taken up with great zeal both in Europe and this country; and contrary to Henry's fundamental and, as time has shown, prophetic conception of the field of the electro-motor, it was everywhere confidently supposed that in time it would supersede steam. In this expectation the misunderstood electro-motor disappointed the hopes reposed in it and for a time it was in disgrace; but, not a success certainly as a prime mover, it has found its place and it is exactly the place to which it was assigned by Henry; it is the assistant of steam, not its rival. Its value lies in its capacity to receive power from a distant source and to transfer it without waste immediately to where it is needed. Mr. Pope says: "Henry accurately foretold the true place, in the domain of industry, of the electric motor. Much confusion of thought exists in the popular mind of the present time in reference to this very point. * * * *Electricity,

in its important application to machinery, is never in itself a source of power. It is merely a convenient and easily managed form of energy, by which mechanical power is transferable from an ordinary prime motor, as a steam engine or a water wheel, to a secondary motor which is employed to do the work. It performs an office precisely analogous to that of a belt or line of shafting, which, however useful in conveying power from one point to another, can, under no conceivable circumstances, be capable of originating it." 5

In comparison with other modes of transmitting power the electro-motor is well nigh indifferent to the extent of the distance from the source of its power. Who made the instrument thus indifferent to distance? Let us go back to it as it was in its infancy in 1831, in Henry's cabinet. Henry knew that his magnet, in the telegraph in the upper room, could respond as easily to its battery if that one mile of wire stretched around those walls were extended to hundreds; and he knew as well that his little machine could be made to work if its batteries were equally far away. The means of producing electro-mechanical effects at a distance, this was what Henry had discovered, and in this machine he showed how the power might be used in other ways than in the telegraph.

"In 1834 Dr. Edmonston of Baltimore published a description of the rotary motor, a modification of Henry's arrangement, and these two forms are the prototypes of all the electro-motors, which have been constructed from that day to this."-(Frank. L. Pope.)

Henry's friends urged him, not only to take out patents for his magnets and his telegraph, but also for this machine. Hundreds of patents have been granted in this country for modifications of the electro-magnetic-telegraph, and as many for varieties of the electro-magnetic machine; all of which would have been tributary to Henry as the original patentee. His constant answer to all such solicitations was, "My desire is to add to the sum of human knowledge; what I give, I wish to give freely."

PUBLIC SPIRITED JOURNALISM.

IT will be remembered that some time ago the London Electrical Review assumed the uphill task of endeavoring to expose the tricks and wiles of "electric belt" quackery, and as a result became involved in lawsuits for libel, which it had the deserved good fortune to win, although as might have been expected, the quacks are still rampant, for the general public rarely reads technical literature and the daily papers persist in printing the quacks' advertisements.

The Electrical Review obtained damages, with Science Siftings, its colleague in the fight, and Mr. J. Swinburne now has returned to the subscribers to its Defence Fund the entire amount of their subscriptions less a small percentage to cover expenses of printing, stationery, postage, etc. The Review is entitled to the congratulations of the electrical profession on its success in this fight, and to admiration for its honorable and public spirited action throughout.

5. Electricity in Daily Life, Chas. Scribner's Sons, New York, 1891, page 41. (Reprinted from Scribner's Magazine.)

Electricity Up to Date. By John B. Verity, London and New York. F. Warne & Co. Paper, 226 pp. illus. Price, 75 cents. (Fourth Edition).

Mr. Verity's useful and handy little book reaches us again, and we can only repeat of this what has been said of previous editions, namely, that it is one of the best of the popular books. There is nothing pedantic about it, yet nothing foolish or inaccurate. It tells the story clearly and plainly, and every page is interesting. Such a book ought to reach its fortieth edition, with constant and careful revision.

Premiers Principes d'Electricité Industrielle. By Paul Janet, Paris, Gauthier-Villars et Fils. 1893. 275 pages, 5%1⁄2 x 81⁄2. Price $2.

This is a reproduction of a course of lectures delivered by the author at the Faculté Des Sciences of Grenoble, and is intended therefore. more particularly for students. It carries the reader through the study of batteries, including primary, secondary and thermo cells, dynamos and transformers. The book is devoted more to inculcating the principles of these various types of apparatus, giving only such details of construction as to enable the student to form a fair idea of the actual apparatus, all the standard types of which are illustrated. The book is well up to date and the explanations are quite lucid.

Reference Book of Tables and Formulas for Electric Street Railway Engineers. By E. A. Merrill, Author of "Electric Lighting Specifications." New York. The W. J. Johnston Company, Ltd., Flexible Morocco, Pocket Size. Price, $1.

The appearance of this little reference book is very timely as it puts in the hands of the electric railway constructor and superintendent a considerable amount of valuable information. The author has followed the plan of beginning with the steam plant and passing successively through the subject of cars and their equipment, overhead work, track work and miscellaneous tables and formulas. While the works of the best authorities have been consulted, a number of tables and formulas are original, and many others have been modified and extended to adapt them to the conditions imposed in electric street railway work.

Standard Tables for Electric Wiremen, With Instructions for Wiremen and Linemen, Underwriters' Rules, and Useful Formula and Data. By Chas. M. Davis. Fourth Edition. Thoroughly revised and edited by W. D. Weaver. Flexible morocco. 128 pages. Price, $1.

This very handy little work has recently received a thorough revision at the hands of Mr. W. D. Weaver, and among the new things embodied in it is the calculation of alternating current wiring. These include tables of alternate current wiring coefficients, those on alternating currents for exterior wiring and on the candle power of arc lamps, and tables enabling those for the three standard lamp voltages to be used for any voltage or drop; as well as several others, including a complete set of wiring tables calculated on a uniform basis of 55 watt lamps. In addition we find a good deal of valuable miscellaneous information in the book.

Dynamo and Motor Building for Amateurs, with Working Drawings. By Lieut. C. D. Parkhurst, U. S. A. New York. The W. J. Johnston Company, Ltd., 1893. 163 pages. 5 x 7 inches. Price, $1.

Although the continued manufacture of electric motors of small sizes has brought their price down much below what it was some years ago, there are still not a few who prefer to gain the practice which only actual work propriis manibus can afford. The amateur will find here little or no theory to embarrass him, but straightforward descriptions with diagrams and working drawings, which will enable him to construct three or four kinds of machines, ranging from a small electric motor, driven by battery current, to a 50-light incandescent dynamo. The book has

special value as it represents the author's own experience in this class of work, which he has succeeded in laying before the reader in very clear language.

Twenty-Fifth Annual Report of the Board of [Massachusetts]

Railroad Commissioners. (Pub. Doc. No. 14.) January, 1894.
Wright & Potter Printing Co., Boston. 8°, pp. xix + 311;
Мар.

EACH Succeeding annual report of the Massachusetts Railroad Commissioners devotes an increased amount of space to a discussion of the problems which continually present themselves in connection with the rapid extension of the electric railway service within that commonwealth. While the actual number of street railway companies shows but little increase-in fact, owing to consolidations and other causes, the number reporting is one less than in the preceding year-the aggregate mileage in operation shows, as might be expected, a notable increase. The returns are made up, as usual, to September 30, 1893, at which date, the total length of street railway including double tracks, but not sidings, was 874.14 miles; an increase over the preceding year of 119.29 miles. There has been during the year an increase of mileage operated by electric power of 214.78 miles, and a decrease of mileage operated by horse-power of 95.49 miles. The first successful commercial use of electricity as a motive power in the state is said to have been on the Lynn & Boston line in July, 1888.

The gross assets of all the street railway companies are given as $50,130,273.20, and the gross liabilities as $49,589.687.91. The percentage of surplus to capital stock, which in 1887 was 13.89 fell the following year to 6.82, and has since decreased progressively year by year, until it was in 1893 only 2.09 per cent. A comparison of the traffic returns for the past decade, shows between 1888 and 1893, an increase of 142 per cent. in the passengers carried; of 125 per cent. in number of miles run, and of 96 per cent. in the number of round trips, annually. During the past five years, the average net earnings have increased from $2,420 to $3,810, per mile of railway owned, from 5.56 to 9.65 cents per carmile run, from 40 to 74 cents per round trip run, and from 0.96 to 1.56 cents per passenger carried.

The average cost of the street-railways of Massachusetts per track-mile, as per books of the companies on September 30, 1893, was for construction, $26,792; for equipment, $15,455.06; and for land, buildings, etc., $11,738.63, making a total average cost per mile of $53,985.69. Of course these figures furnish no basis for estimating, even approximately, the cost of any particular railway. The cost of different lines varies, as returned by the companies, from a minimum of $13,745 to a maximum of $98,907 per mile of track.

These results, for convenience of comparison, have been thrown into a table as follows:

The gains which the above table shows in the average net earnings per passenger carried, per mile run and per round trip, ranging from 62 to 85 per cent. in favor of the year 1893, are certainly at first view very striking; and, if these were the only elements in the case, the financial success of the electric system might be pronounced at once to be not only assured, but marvelous. There are, however, other important and decisive factors which must not be overlooked.

In the first place, any increase in the net earnings must obviously be compared with the increase in the cost and capitalization of the electric over the horse system. The manufacturer whose new factory brings him in twice the net income of the old one, has gained nothing in the way of return on his investment, if the new plant has cost him twice as much as the old. So here, the most direct and conclusive test of the net earning capacity of the two systems, is a comparison of the increase in the net earnings per mile of railway with the increase in the cost of the railway per mile. Applying this test, it will be seen that, while the net earnings per mile are 57 per cent. greater, the cost and capitalization per mile are respectively 60 and 65 per cent. greater in 1893 than in 1888,-the odds being clearly in favor of the horse system.

In the second place, it must be taken into account that the electric railways, with their power-stations and electrical equipment, are all of new or recent construction. For this reason, the cost of the maintenance of the new system, which is chargeable to operating expense, has thus far been abnormally small, and the consequent showing of net earnings from operation has been ab normally large. The generation and distribution of electric motive power involve extensive plants, costly machinery and intricate apparatus and appliances, all of which must be kept in perfect working order. The wear and tear of roadbed and track are increased by the heavier rolling stock of the new system. As time goes on, the cost of renewals and repairs cannot but increase or be otherwise than large; and this cost must go into operating expense. The net earning capacity of the electric system will not, therefore, have been fully tested, until time and experience have demonstrated the normal and full average cost of its maintenance; and the net results, as they now appear, must be qualified accordingly.

We must conclude, therefore, taking everything into the account, that there has been thus far no demonstration of the superior net earning capacity of the

electric as compared with the horse system, but rather the reverse. It is not, however, intended to raise the inference that, the electric system is, or is likely to prove, under conservative and proper management, a serious financial failure. The conditions attending its further and fuller development will probably be found to differ in no essential respect from those attaching to the old horse railway system, or to the steam railroad system. It can and should be said however, without hesitation or qualification, that the electric system has not shown or indicated any such margin of profit as to justify the expectation of more than moderate and ordinary returns on money legitimately invested in it. The idea, which seems to have obtained some currency, that the electric railway system is a bonanza of rare and inexhaustible wealth is clearly a delusion, and has doubtless proved to some a snare. The absolute cost and expensiveness of the system, under the most conservative, able and honest management, are sufficient to task its earning capacity to the full limit. There is no margin for fictitious or inflated capitalization. It presents no safe or inviting field for speculative enterprise and manipulation, unless it be to the unscrupulous operators of an inside ring who are willing to practice on the credulity of a misinformed public.

The statistics of accidents show that during the year covered by the report, the total number of persons killed and injured by electric cars was 271, being in the ratio of 1 to each 52,475

miles run.

The Commissioners call attention, in very forcible language, to the rapidly increasing number of grade-crossings of electric and steam railroads, the returns for the year showing the appalling increase in these death-traps of from 26 to 100. They say:

It is not to be believed that the [original] allowance of 100 such crossings outside the public highways would for a moment be thought of. The remarkable condition of things now existing has crept in unawares, as it were, under a code of laws intended only for horse-railway travel, enacted before the operation of street-railways by mechanical power had come to be regarded as more than a remote possibility. Of all the perils which attend travel on railroads and railways in this Commonwealth, there is no one which, in the apprehension of the Board, is so serious, both in its character and extent, as that here pointed out; and the Board would be derelict in duty to itself and the public, if attention were not again called to it, without waiting for some serious casualty-of the imminence of which, hardly a week passes without giving fresh warning-to emphasize the recommendation.

The Board again call attention to the desirability of legislation limiting the amount of bonds which may be issued by streetrailway companies, a recommendation, not acted upon by the last Legislature, but which is obviously quite as much in the interest of all solvent corporations as in that of the investing public, inasmuch as no well-informed person would be likely to invest knowingly in the bonds of any company, with which the market might at any time be flooded to an unlimited extent.

The deductions and observations of so careful and conservative a body of experts as the Massachusetts Commissioners in reference to the questionable profitableness of electric railways as a permanent investment, have not unnaturally given rise to no small amount of comment and criticism. While there is no doubt abundant room for caution in the direction pointed out, and while it must be admitted that there is much reason to fear that as soon as the present financial stringency has in some measure passed away, the extension of electric railways into unprofitable fields may be prosecuted to an extent which cannot but ultimately result in a disastrous collapse, the figures given in the report do not appear to necessarily warrant all the deductions which have been drawn from them. This will appear, for example, from an examination of the comparative results during the same period [188893] of a local street railway, with whose affairs the writer happens to be somewhat acquainted, and which has always been justly regarded as an exceptionally well and liberally-managed system. It serves a manufacturing population something in excess of 60,000. In 1888 this system was operated by horse-power and did not extend much beyond the thickly settled parts of the city. Between that date and 1893, the trackage was increased, in round numbers, from 14 to 33 miles; the system was converted into an electric one: the capitalization per mile was increased from $22,000 to $30,000; the construction account from $11,000 to $18,000, and the equipment account from $5,000 to $10,000. A comparison of net receipts for the same period shows increase per mile operated of $2,260 to $3,000; per round trip of 39 to 53 cents; per mile run a decrease from 8.1 to 6.9 cents, and per passenger carried a decrease from 1.4 cents to 1.3 cents. Nevertheless, the company has never once failed, during that time, to pay its regular dividend of 8 per cent., and it has actually a larger surplus to-day than it had in 1888, notwithstanding there has been a trifling increase (from 74 to 75 per cent.) in the ratio of gross expenses to gross income. The falling off in net income, per mile run and per passenger carried, has been caused by the extension of the company's tracks into thinly settled suburban districts, but it is evident that within the next ten years, the increase of population along these suburban routes, will materially augment the gross receipts, without adding in anything like the same proportion to the necessary expenses. It will be contrary to all previous experience, also, if the actual cost, per car mile, of operating an electric railway should not be largely reduced by the progress of science and invention during the same period. This example however, only serves to enforce the moral drawn by the Commissioners, that an electric railway, no less than any other, must be judiciously located and carefully managed, if it is expected to be profitable.

an

F. L. P.

THE LYNCHBURG ELECTRIC COMPANY's first mortgage 6 per cent. 25-year gold bonds are offered at par and accrued interest.

LETTERS TO THE EDITOR.

INTRODUCING THE QUADRUPLEX INTO ENGLAND. MR. W. H. PREECE, C.B., F.R.S., in a paper entitled, "Notes of a Trip to the United States and Chicago, 1893," published in the Journal of the Institution of Electrical Engineers, Volume XXIII., No. 109, March, 1894, as the result of an official visit and inspection of the telegraphic system of the United States in 1877, speaks among other things of the practical introduction of the quadruplex system on the Government postal lines. The subscriber hereto is thus reminded of his most delightful visit abroad, the cordial welcome and generous hospitality extended to Mr. George A. Hamilton and himself during their two months sojourn in London and Liverpool having on hand the pleasant and easy task of establishing quadruplex working between the points named.

In view of the openly expressed doubts as to the success of the system abroad, the trial was looked upon as purely in the line of experiment; and predictions were freely made that stormy weather, with the usual accompaniment of a London fog, would prove an effectual barrier to its successful working. It was therefore with considerable pride that from time to time during the first week or two, information was communicated to Mr. Preece of the satisfactory working during weather that proved almost too much for the duplex circuits between London and Liverpool; but these occasions served to indicate what might be expected when the now anxiously looked for London fog should arrive.

The patience of my faithful co-operator at the Liverpool end was soon rewarded by the arrival of a storm from across the Atlantic bringing with it conditions for the development of a veritable London fog which reached a maximum density about 11 a. m. when even the street traffic was rendered somewhat perilous. The service with Liverpool opened rather tardily upon all the regular circuits, the quadruplex being the exception. It was at once supplied with business for all sides owing to the partial suspension of other circuits. At about ten o'clock a. m. the various duplex circuits between the London and Liverpool exchanges and main offices began to fail, and at eleven o'clock the condition of circuits had arrived in which it was deemed useless to attempt further working, and with the various Liverpool files well filled with business awaiting transmission the following memorandum was dropped to Mr. Preece: "11 a. m., Liverpool duplexes all suspended work. Quadruplex working finely four sides."

In less than five minutes Mr. Preece came to the operating room accompanied by Mr. Patey and a sufficient number of the officials from the various departments interested to form a complete circle around the quadruplex table, at which four operators were easily working, two sending and two receiving. Among the group also was Sir William Thomson, whose interest in the exhibition was clearly shown by earnest inquiries respecting details of the service, condition of the line, etc.

The experimental stage having been so successfully passed, the incident above narrated is put on record as part of the heretofore unpublished history of the introduction of multiplex telegraphy abroad; I will simply add thereto the following clipping from the Telegraphic Journal of December 1st, 1877, as follows:

"The quadruplex instruments continue to work excellently well between London and Liverpool. There can be no doubt that the system is a perfect success. Messrs. Gerritt Smith and Hamilton who have so ably superintended the setting up and working of the apparatus have returned to America." GERRITT SMITH. NEW YORK CITY, April 14, 1894.

DESIGN OF CONSTANT TORQUE VARIABLE SPEED motors.

As a subscriber to the ENGINEER I wish to ask a few questions in regard to a motor intended for variable speeds and such work as requires nearly the full torque or pull at almost any speed. The speed desired is to be widely variable, and yet it is desirable to operate with as little current as possible and as near full voltage at the motor terminals as possible.

How would a series motor with some form of commutated field controller answer the purpose? What would be the average electrical efficiency of such an equipment? Is there a better way than the "commutated field" method of doing this, when one wants in use but one motor?

motor may be run at constant speed although the work may be done under variable speed and torque, such as the various epicyclical gears, invented by Henry, Main, Beaumont, and others.

For using only one motor, and where mechanical complication is inadmissible, the only resource is the commutated field series motor. It is impossible to give directions for the winding, without predetermining the characteristic of the machine, by Hopkinson's method or some modification thereof. For this one would need all the data, sizes, proportions, in fact, working drawings, and also the necessary data as to what the motor is intended for, the circumstances and conditions of its use, whether its service is continuous or intermittent, etc. It all depends on how skillfully the magnetic circuit is designed. In a word, the design and proportions involve careful planning and calculation which should be done by a skilled, experienced, and generally competent person. Even then, it is not unlikely that there will be some modifications required in the first machine made, before it is exactly satisfactory. Some information on this subject will be found in papers read before the American Institute of Electrical Engineers, by H. F. Parshall, "Methods of Electrically Controlling Street Cars," April, 1892, and by Geo. D. Shepardson and E. P. Burch, “Electric Railway Motor Tests," June, 1892.

As for the efficiency it will depend largely on the conditions of operation, the relative steadiness and constancy of load, etc. Probably the only conclusive way to determine it is by actual test. EDS. E. E.]

PATENTS AS ASSETS.

I have read your editorial and those of other journals on the General Electric Co.'s report and note more particularly the reflections on those "ghostly" assets, viz., patents, franchises, etc. I am sure it is not your intention to reflect in any way on the labors of the inventors and electrical engineers, but it seems to me you are doing so in a very pronounced way.

You are aware that the General Electric Co. have acquired property rights in the inventions of Brush, Edison, Thomson and a thousand other inventors of less note who have been mainly instrumental in developing (at an enormous cost) the principal electric arts, which in this country alone are saving the time and adding to the convenience of at least a million inhabitants daily.

Is the laborer worthy of his hire? Do you know of any of them who has been overpaid? Do you think from the knowledge you have of the cost of these developments (which are supposed to be protected by patents) that they and their legal protection have actually cost much less than the amount credited to this asset?

Your idea appears to be that the value placed on those patents is mainly a fictitious one, that they are not worth what they have cost. Mine is, that it is greatly underestimated. Neither of our opinions will amount to anything until the courts of last resort have done their guessing.

One of the journals advises the Company to wipe out the patent asset, stop all litigation, and confine themselves strictly to a manufacturing business. My idea of the theory of anarchism is conveyed in the advice: Don't protect patents but open the gates and let everybody profit at the inventor's expense and labor.

Where would the electrical industries be which we are now enjoying had such policies prevailed during the past twenty years? When you bear on the value of electrical patents you tender discouragement to the electrical engineer.

I hope you will pardon my criticism. I was afraid you had not given the inventor's side due consideration and I hoped to get you thinking in the interest of the inventor. JNO. C. HENRY. WESTFIELD, N. J.

[An examination of its files will acquit THE ELECTRICAL ENGINEER of any intention, from first to last, to reflect at all on the labors of inventors and electrical engineers. Of course the laborer is worthy of his hire and we should be glad if he were always sure to get it.

How much of the $8,159,000, standing for the value of patents and franchises in the General Electric report, does Mr. Henry think ever reached the pocket of the inventors? EDS. E. E.]

THE STORAGE BATTERY CHALLENGE.

IN reply to the challenge of the Chloride Accumulator Co. we wish to say that there are several reasons why we do not wish to take up that challenge. A fear that our battery, working under the conditions for which it was especially designed, will suffer by comparison with the Chloride accumulator is not one of these reasons. We are ready to supply Mr. Gibbs with all the DonaldsonMacrae batteries he may order at our list price with best trade discount, and would be pleased to have them tested not only by Messrs. Houston and Kennelly, but by everyone in the United States who is interested in storage batteries.

BALTIMORE, MD., April 6, 1894.

WM. W. DONALDSON, Pres.

MISCELLANEOUS.

DESTRUCTIVE EFFECT OF ELECTRICAL CURRENTS ON SUBTERRANEAN METAL PIPES.1-I.

BY ISAIAH H. FARNHAM.

FOR the past year or more, there have been read befor water, gas and electrical engineering societies all over this country, papers on the subject of electrolytic corrosion of water pipes, gas pipes and lead cables. In fact a meeting of such societies is incomplete to-day without some discussion on this subject. It was, therefore, with hesitation and misgivings, that I considered the written invitation from the officers of the Institute, to prepare a paper on the "Electrolytic effect of currents on subterranean gas

+

rosion was so severe, and located in spots only, that it led me to attribute the cause to electrolytic action from the railway currents, and a letter was written to my company to that effect.

A few months later, the lead covering of a cable (No. 208) resting upon the ground in manhole chamber No. 76, located at the corner of Berkeley and Newbury streets, was found eaten entirely through at the point of contact with the earth. I then felt certain that the cable had been destroyed by the action of the current. With Mr. W. X. Towne, my assistant, I proceeded to prove the theory.

We took measurements between the cable and the earth, the cable having been repaired and raised from the ground, and found 1.5 to 2 volts difference of potential, the cable being positive to the earth. A barrel of earth was procured from an excavation in the street, a metal plate placed beneath the earth in the barrel, and two short pieces of lead cable placed side by side on top of the earth. The plate in the bottom of the barrel was then connected to the negative side of a storage battery giving 4 volts potential, and one piece of the cable lying on the earth, was connected with the positive pole of the storage battery. The second piece of cable in the barrel was left without electrical connections. The earth was then saturated with water and the circuit was closed, allowing the current to pass from battery to cable, to earth, to plate and to battery, for seven consecutive days. The pieces of cable were then removed and the piece which had been connected with the battery was badly pitted, closely resembling the cable

and water pipes." A prominent officer of the Institute urged that, as I was undoubtedly the first to discover and satisfactorily prove that this action was destroying cables, I ought to give the Society an account of my investigations and the results. On this suggestion, the promise was made to lay before you such facts as opportunity would allow. If sufficient data may be presented to form a nucleus for the evening's discussion, it will, I am sure, be of some practical value.

FIG. 3.

which had been destroyed, while the second piece of cable showed no corrosion whatever, proving conclusively that a current such as was found in the manhole, was sufficient to cause the damage that had been found, and that the corrosion was not, in the case of the experiment at least, due to any acid or salts in the earth. Fig. 1 shows the barrel experiment, and Fig. 2 is a photograph of the cable No. 208, which has been described as found resting on the earth in the manhole chamber and corroded through; also the pieces experimented upon in the barrel. That shown in the centre of the photograph is cable No. 208.

In addition to the experiment just mentioned, we placed in the bottom of manhole chamber No. 76, two short pieces of cable,

LEAD CABLE

FIG. 2.

Early in the summer of 1891, some lead-covered telephone cable removed from wooden ducts in Boston, showed some very marked yet local spots of corrosion. The cause of the corrosion was generally attributed to acetic acid contained in the wooden conduit, which had, years before, caused corrosion on a few cables in certain sections of the city. In the case just mentioned, the cor

1. Read before the American Institute of Electrical Engineers, New York, April 18, 1894.

FIG. 4.

one of which we connected by a wire to cable No. 208, which had been damaged by electrolysis. (It should be understood that the damaged cable had been repaired, and removed from the bottom of the chamber.) At the end of six weeks, the pieces of cable were removed and examined. The one which had been connected with cable No. 208, was deeply pitted,' while the other piece was free 2. The plumbers of Omaha, Neb., apply the name of "small-pox pipe" to that pitted by electrolysis.

from corrosion. These experiments, with several others of minor importance, satisfied all who were interested, that electrolytic action was destroying cables, and probably gas and water pipes. It next became necessary to prove to the electrician of the railway company, that the current causing electrolysis, was from the railway system and not from a leak in the Edison or some other electric lighting system.

Measurements were made between the cables in all manholes and the earth near the cables, for voltage and direction of current. It was found that within a radius of about 2,000 feet from the Albany street power house, cables were negative to the earth, ranging from zero to 2 volts, and that outside of this neutral line, they were positive to the earth from zero to 12 volts. This condition prevailed until a point was reached near the East Cambridge power house, when they again passed a neutral line and became more and more negative as that power house was approached. The same conditions were found as the Allston Railway power house was approached. On obtaining sufficient data, maps were drawn, showing voltage between cables and earth throughout all sections of the city. This is shown in map, Fig. 3. In addition to the figures placed beside the several routes of cable conduits, showing the direction of current and its pressure, we have colored red (shaded), each portion of the map where at that time we found the cables positive to the earth. We may call the red portion of the map, the danger territory. These potential measurements, though taken for other purposes, incidentally furnish

was tried on an extended scale, but though many ground plates having a surface of several square feet each, were connected with the cables over a large portion of the city, it was found that voltmeter readings taken between the cables and a point on the earth a short distance removed from the ground plate in any manhole, gave nearly the same pressure as before the ground plates were connected. In some cases, the voltage between the cables and the earth was reduced 25%; in many others no noticeable reduction was made. The ground plates were constructed from pieces of old lead cable, 6 to 10 feet in length and embedded in the wet earth at the bottom of the manholes. It was evident from this test, that ordinary ground plates would not prove of material advantage for protecting the cables.

Third.-Prof. Elihu Thomson suggested, among other possible remedies, the placing of motor generators at different points along the railway line, wherever the cables and pipes are found to be in danger, the motor generators to be operated by the railway power current; the secondary current developed by these generators to

FIG. 5.

FIG. 6.

all the proof needed to convince one that the railway power was the source of the troublesome currents.

At the time the map was made, and previously, the railway was operating with the negative pole of the dynamo to the trolley, the positive side being to the rails. Fig. 4 is intended to illustrate this condition. It shows the passage of current from the dynamo to the rails, and the passage of a portion of the current from the rails to the cables within the neutral or zero line, and from cables to rails outside of this zero line. The danger of electrolysis is only where the current is leaving the cable or pipe through the moist earth, hence the dangerous district was at this time outside of the zero, or neutral line, as shown both on the map (Fig. 3) and in this Fig. 4.

Having outlined our early experience in running down this new trouble, we will now mention some of the proposed and applied remedies. Several conferences were held for the purpose of suggesting and discussing means for preventing the destruction of the cables, at which the officers and experts of both the railway and telephone companies were present, and it should be said, that the railway company in Boston has shown a disposition to adopt any promising plan for overcoming the evil, save, perhaps, the abandonment of the rails and earth as a part of the circuit.

First.-It was proposed to remove all cables from the wet bottom and sides of the so-called manholes. It was found very difficult to place and retain cables free from the wet sides, and even could this have been accomplished, the action at the mouth of the ducts, and within them would still have continued. They were, however, all removed from the bottom of the manholes.

Second.-It was suggested that the cables might be connected to ground plates in the manholes, and so transfer the electrolytic action to these plates, and thus save the cables. This experiment

FIG. 7.

be utilized to lower the potential in the cables and pipes to zero, with respect to the surrounding earth or rails. The suggestion included means for automatically starting and stopping the generators, as cables might become positive or negative to the rails. The motor generators would, so to speak, pump the current out of the cables and force it into the rails whenever the potential of the former should rise above zero. Fig. 5 illustrates this suggestion. This plan has not yet been put into operation so far as I am aware.

Fourth.-Insulating the cables and pipes from the earth was proposed. As some of the worst cases of corrosion of cables by electrolysis occurred where they were painted with asphalt, taped, painted again, and finally covered again with heavy braiding also saturated with asphalt, it was apparent that to insulate cables sufficiently to protect them would be difficult and expensive, if indeed practically possible. To protect water and gas pipes by a sufficient insulating jacket was seen at once to be impracticable.

Fifth.-Breaking the metallic continuity of the cable sheath and pipes was proposed. From the fact that severe action is frequently found in comparatively isolated spots, where cables and pipes cross each other or pass near or across the rails, it follows that any system of breaking the metallic continuity, would have to be studied with reference to the entire complicated system of pipes, cables and rails ramifying through the streets of a city. There would also be a difference of potential between the several sections of cable or pipe, severed metallically, tending to cause electrolysis at one end of each section, as illustrated in Fig. 6. In case of water pipes, treated in this manner, the action might be expected on the interior as well as on the exterior.

There appears to be some evidence of such an action as this in gas and water pipes where the electrical continuity is partially