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motion is reversed. The car is provided, in addition to the usual hand-brake, with a very powerful magnetic brake, and with an automatic arrangement which puts this brake on if the speed exceeds a certain limit.

A car built on this principle has lately1 been supplied to the Berlin Tramway Company, and formed the subject of an interesting paper by Herr Zacharias, read in January, 1886, before the Elektrotechnischer Verein,' in Berlin, to which the reader is referred for full particulars. Each motor weighs 420 lbs., or, both together, inclusive of the gear, about half a ton. The accumulators, with their trays and accessories, weigh 1 ton. They have to be changed every two to four hours. The total weights are as follow:

Car, with motors, gear, and accumulators 46 passengers, conductor and guard

Total

3.75 tons.

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2.25 tons.

6.00 tons.

The tractive force required on a level average road is 30 lbs. per ton, and at a speed of seven miles an hour this represents about 3 horse-power work done.

Herr Zacharias makes the following comparative estimate as regards the cost of horse traction and electric traction. He assumes that each car is actually in use from five a.m. until one a.m.—that is, for a period of twenty hours per day—and that it requires a change of horses every four hours. This gives five pairs of horses per day per car.

A line worked by sixty cars would, therefore, require 600 horses actually in service, and say ten per cent. in reserve, or 660 horses in all.

more

1 December, 1885. 2 "Elektrotechnische Zeitschrift," Jan. 86.

COMPARATIVE ESTIMATES.

305

To work the same line on the battery system would require steam power up to 750 horse-power, and a proportionate amount of electrical plant as given below. The capital outlay becomes

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Thus the first capital outlay is for electric traction only slightly greater than for horse traction, and if we consider that the buildings necessary to accommodate steam and dynamo machinery of a total power of 750 horsepower are not so extensive, and do not cover as much land as the buildings required to accommodate 660 horses, the balance in the first outlay may probably be in favour of electric traction. The working expenses are certainly much lower for electric traction. Herr Zacharias estimates as follows:

I. Working Expenses with Horse Traction:Depreciation per horse per day 0.4840 shillings.

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II. Working Expenses with Electric Traction:

Annual expenditure of energy, 6,570,000

horse-power hours.

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According to these estimates the annual working expenses of electric traction on the Reckenzaun system would only be about half as great as with horse traction.

CHAPTER XII.

M. Marcel Deprez's Experiments-Palais de l'Industrie in 1881-Munich in 1882-Paris, Gare du Nord, in 1883-Grenoble-Vizille, in 1883-ParisCreil, in 1885-The Generator-The Motors-General ArrangementRegulation of Motors-Starting of Motors-Stopping of Motors-Automatic Safety Appliances.

M. MARCEL DEPREZ is one of the earliest pioneers in the electric transmission of energy. It has already been stated in the introductory chapter that although the invention of electric transmission is not due to him, his is the merit of having first attempted long-distance transmission on a practical scale. Ever since M. Hippolyte Fontaine exhibited an example of electric transmission of energy at the Vienna International Exhibition in 1873, scientific men and practical engineers have realized that the success of the system, when applied to long distances, depends simply on the possibility to work with high electro-motive forces. If it be possible to construct generators and motors suitable for a pressure of several thousands of volts, and if the insulation of the line can at that pressure be maintained perfect, then the question is solved, and we shall be able to transmit economically and with certainty a considerable amount of energy over long distances.

Whilst most electricians who investigated the subject rested content with a solution on paper only, M. Marcel Deprez had the courage to carry his investigations into

actual practice. It cannot be denied that his first experiments were, on the whole, failures, and even the latest example of transmission, that between Paris and Creil, is not altogether a success: but they are, nevertheless, very instructive, and show a gradual improvement, as will be seen from the following short history, arranged according to the date of these experiments.

1881. Palais de l'Industrie at the Paris Electrical

Exhibition.

The generator was a Gramme dynamo, the field magnets of which were wound with two distinct circuits, one carrying a constant current from a separate exciting dynamo, also of the Gramme type, and the other being in series with the external circuit. This generator was, probably, the first compound machine made since that of Varley, though not compounded in the same way as Varley's machine, and not as we now understand the term. The current was distributed between various motors placed at different points in the building, all the motors being in parallel connection, and each motor could be started and stopped independently of the others. The motive power was furnished by a 4 horse-power gasengine. No trials as regards efficiency were made, and the chief interest of the exhibit lay in this, that it was shown that the transmission and distribution of mechanical energy by means of electricity was not only possible on paper but an actual fact.

On this occasion, in a paper read before the Congrès International des Electriciens, M. Marcel Deprez gave it as his opinion that it would be possible to transmit 10 horse-power over an ordinary telegraph wire to a distance of 30 miles, the energy expended at the generating station

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