The following experiments were made by Mr. Purinton to determine the actual speed of slip of a 10 in. double belt, which transmits power (advantageously up to about 16 H.P.) from the fly-wheel of a Harris-Corliss engine.

From these experiments it would seem that Mr. Towne's coëfficient is too large, and although we have not experimented with speeds between 13 and 30 ft. (our speed being nearer 2 ft. per. m.) the coefficients determined must be nearer the truth than those obtained with 200 ft. of slip per minute.

The experiments will be continued and we hope eventually to be able to formulate: I. The maximum power, which a given belt running at any given speed will carry. II. The amount of slip of the belt when running at a given speed and transmitting a certain amount of power.

STEAM ENGINE TESTS. By Prof. C. H. PEABODY, Boston, Mass. [ABSTRACT.]

In the winter of 1883-4 a number of experiments were made by the fourth year class in the mechanical laboratory of the Massachusetts Institute of Technology, the results of which are here given. They were made mostly on an 8" X 24" Harris-Corliss engine running with a normal speed of 60 revolutions per minute, the power being absorbed by a friction brake, and the steam being condensed in a surface condenser at atmospheric pressure and afterwards weighed. A fairly uniform back pressure was produced, when required, by throttling at a distance from the engine. The

tests lasted usually about 100 minutes, with indicator cards from both ends of the cylinder, and readings of the number of revolutions, boiler pressure, and weight of condensed water every 5 m.

In experiments 1 to 4 the cut-off was varied; 5 and 6 show a lower boiler pressure; 7 and 8 a large back pressure; 9 and 10 were made with a throttling governor; and 11 was made at about half normal speed. The horse power and point of cut-off were obtained from the indicator cards. The percentages of steam at cutoff and release were obtained by calculating, from the cards, the weights of steam in the cylinder at those points, and dividing it by the weighed amount of water used per stroke plus the weight, obtained from the cards, of steam in the cylinder during compression. The difference of these two percentages is the per cent of reëvaporation.

The most noticeable feature of the tests is the large quantity of water per H.P. per hour, and the excessive reëvaporation due to short cut-off. Various other points will appear upon a careful comparison of the data.

Three tests were made with a Porter-Allen engine, but the data obtained indicate nothing worthy of remark.

ECONOMY OF THE ELECTRIC LIGHT. By ALLAN STIRLING, N. Y.

City.

THE combustion of carbon is the source of the light with both gas and electrical lighting, but a marked difference occurs from the fact that in the former case the carbon must be carried to the point where the light is needed, while in the latter it is burned under a steam boiler at any suitable place, and only the resulting energy in shape of electricity, need be carried to the lamp.

To compare the two systems assume ten blocks of houses requiring in all 12,000 seventeen candle power lights; suppose that in summer one-third of these will be used three hours per night, and in winter two-thirds for four hours. The cost of gas in N. Y. city for these lights will be at the rate of five feet per burner and $2.25 per thousand feet-$24,600 for the summer half, and $65,700 for the winter half of the year; total $90,300.

The items of the cost of electric lighting are; coal and water for boilers, attendance, lamps, miscellaneous supplies, repairs and depreciation, interest. At the rate of one horse-power for every eight lights, and three pounds of coal hourly per horse-power, with coal delivered at $5 per long ton, the yearly coal bill will be $6750. For water $457 will be needed, supposing 27 lbs. needed per horse-power, at 13 cents per 1000 gallons. With lamps costing 90 cents each and lasting 600 hours the cost of renewals would be $12,000. For miscellaneous supplies $750 may be allowed. By properly directing and economizing the labor of the attendants the work may be done by one engineer and one or two firemen, so that, at $4 and $2.50 respectively, we shall need $2800 for attendance.

The plant will cost say $15,000 for ground and buildings, $50,000 for engines and boilers and $40,000 for dynamos, and the cost of wiring and fixtures may be omitted to balance the cost of pipes and fixtures for gas. For repairs and depreciation on this plant we will allow $10,500, with a like amount for interest. The total yearly amount will therefore be $43,800, giving a difference in favor of electricity of $46,500, and showing that the latter can be furnished at less than half the present price of gas or as cheap as it would be at $1.12 per thousand; or, supposing we divide the saving between the electric light company and its customers and

put the price equal to gas at $1.69 the company would earn 20 per cent. additional, making its profit in all 30 per cent.

A further and most important saving can be made by heating the buildings by means of the exhaust steam from the engines, so that in winter but a part of the whole expense could be chargeable to the electric lighting, $8000 to $9000 might thus be saved, bringing down the cost to that of gas at $1.48 while affording seven per cent additional profit. The largest item of cost is lamprenewals and we may be reasonably confident that the average life of lamps will be greatly increased and that their cost will be much reduced. There seems to be therefore no reason why the electric light for domestic purposes should not at once be a paying investment, as it is known to be in numerous cases where isolated plants have been introduced in manufactories, and other places of business.

TRAINING FOR MECHANICAL ENGINEERS. By Prof. GEO. I. ALden, Worcester Free Institute, Worcester, Mass.

[ABSTRACT2.]

PROGRESS in education is secured by the aid of forces outside and above the schools. When a few have made discoveries in science or advancement in art or in engineering they have set a standard which must thereafter be the aim of educators. Mechanical engineering as taught in schools is subject to the general law of progress. While it is taking a high rank as a liberal profession and offers a broad field for the activity of the best powers of young men who enter it, yet it must look for progress to two main forces,

1This paper was presented in response to the announcement of the Secretary, that one or more sessions would be devoted to the discussion of the "Best methods of teaching mechanical engineering." Owing to a variety of untoward circumstances, other expected papers did not come to hand in time, but an exceedingly lively and interesting discussion was aroused. This was participated in by a number of prominent mechanical engineers and teachers and other scientists, and it was unanimously decided that the discussion must be continued. The following gentlemen were accordingly appointed a committee to secure the active coöperation of leading men in a fuller presentation and discussion of the subject at the next meeting: J. Burkitt Webb of Cornell University, Ithaca, N. Y., Geo. I. Alden of Worcester Free Institute, Dr. C. M. Woodward of Washington University and A. Beardsley of Swarthmore College. 2 Printed in full in the American Engineer, Oct. 3 and 10, 1884.

viz., the influence of the scientific attainments and practical achievements of those foremost in engineering science and practice. A school for training mechanical engineers is properly a professional school, and should hold up its standard of professional training, in order that it may demand in candidates suitable preparatory, general training for matriculation. It should aim to fit young men for immediate usefulness in the profession, and to lay the sure foundations for a growth which shall enable them to take up the unfinished work of the engineers of this generation and carry it forward into the next century of progres. To aim at practical achievements is not enough; for the man is more than his profession. Scientific attainments are not alone sufficient. The ability to apply knowledge to practical ends is valuable in discipline as well as necessary to professional success. The necessary scientific attainments are more than mere knowledge of facts and principles. The evidence of such attainments is the ability- within a sufficiently wide range of inquiry to give accurate answers to definite questions. To secure this ability the usual studies in the curriculum of the schools should be thoroughly taught by direct methods, with the aid of numerous and well selected problems, and laboratory work. The problems should be, as far as possible, actual engineering problems that the student may secure that complete assimilation and personal appropriation of the subjects taught throughout the course, which characterize the scientific attainments toward which the school should aim.

The practical achievements of the engineer are closely related to machine-shop methods and practice. All his designs must be sent to the shop in a form consistent with such practice. To secure knowledge of machine-shop methods, limitations and possibilities, most schools have a practical or shop department in their engineering course. It is important that the successful engineers of the country should say what such a shop should be and what it should accomplish. The shop is made a department in the course in order to add to the school methods as well as to its facilities for instruction. It should not, therefore, be such an institution as would be developed by, or out of, the school. It should bring to the school its own methods and standards. It should be superior in all its appointments for practical, constructive and engineering work. It should have not only the tools, methods and facilities but also the business of a leading productive shop. It will then