tacks the lead plate to which it goes, thus forming peroxide of lead, and the hydrogen reduces any oxide that may be on the other lead plate, thus producing pure lead, some of the surplus hydrogen forming as a film upon the surface. The charging current is then reversed, so that the latter plate is now attacked, and is then reversed again; the effect of these operations being to render the surfaces of both lead plates porous so that they present a large surface, and can therefore hold a great deal of peroxide of lead. When the charging current is broken, the oxygen, which has been forcibly separated from the liquid, seeks to recombine in the same way that a stone which has been forcibly separated from the earth seeks the earth when liberated. If now the two lead plates be joined with a wire, the effect of the oxygen in the peroxide of lead trying to recombine is to generate an electrical current in the opposite direction to the original one; and this is the current which is utilized. The value of accumulators would be much increased if this return current could be made greater, and if the weight and cost of the accumulators themselves could be made less. At present, however, their use is restricted by reason of their great cost and weight, and by the small ratio (about fifty per cent in practice) of the electrical energy returned to that expended in charging them. Nevertheless, the fact that the accumulator system of electric railroading obviates the necessity for any conductors, which sometimes are inconvenient and expensive, and which themselves occasion great loss of electrical energy, leads many to believe that for short routes, as upon street-car lines of cities, accumulators will be very efficient.

FIG. 3.

At the Chicago Exposition of Railway Appliances, which has just closed, the system of Messrs. T. A. Edison and S. D. Field, of New York, was tried, and with undeniable success. By this system a third conductor is used; but it is not placed upon poles, as in the Siemens system (for this would not be practicable in the streets of a city), but lies in a long sunken trough which runs between and parallel to the rails. The trough is covered, and a long and very narrow slit runs the whole length of the cover. Through this slit extends a strong metallic rod which is connected mechanically with a contact-carriage lying upon the conductor, and which is mechanically and electrically connected with the car.

It is claimed that by means of a scraper, carried by the contactcarriage, there will be no trouble occasioned by any accumulation on the conductor of ice, snow, or mud, but that the car can be satisfactorily run in all kinds of weather.

Fig. 4 represents the generator and track as arranged at the Chi

cago Exposition. It will be noticed that one pole of the generator (dynamo) is connected with the auxiliary middle rail, and the other with one of the two side-rails which are metallically connected together, as shown. The current goes to the motor on the car by the middle conductor, and is returned to the generator by the side-rails.

56 feet.

Rac

The advantages of the electric railway, should it be made practicable in all respects, are obvious, and there is good reason for believing that in time it will be made available and economical even for lines of considerable length.

In the streets of a city, electric cars would be advantageous upon the surface roads for the reason that they could be run more quietly and swiftly than horse-cars, and, as an electric car can be stopped in less than its own length, just as safely; in crowded parts of the city, they could thread their way more rapidly through the crowds of carts and other vehicles, because they can be stopped and started more quickly and require less room. But it would be upon elevated roads that their advantages would be pronounced, for we should then escape much of the noise and all of the smoke and smell that now attend the passing of elevated trains.

Generator

arrival and departure, so that to reach the

By reason of our abil ity to make every electrical car its own locomotive, it is clear that we can secure greater safety in traveling, and greater frequency in the times of depot half a minute too As each car is very

late would not be so serious a thing as it now is. light, it can be stopped in a much shorter distance than is now possible with a heavy train; and, even if a collision should occur, it would not

be such a horrible thing as a collision between two ponderous trains, not only because of the lightness of the electric cars, but also because they do not carry steam and fire as locomotives do. Another advantage of the lightness of the cars lies in the fact that they will exert less 66 wear and tear" upon the tracks, and therefore occasion less outlay for repairs.

When the present mode of traveling in Pullman cars is compared with the mode in use not very long ago, by which people were cramped for hours and even days in a coach without springs worth calling by that name, and were jolted and tossed about over uneven roads, we conclude that traveling at the present time is a very luxurious thing. But what will it be when we can sit at an open window, and glide along at the rate of sixty miles an hour, without the fear of smoke or cinders; when electric bells are at hand leading to the inaccessible retreats where porters now secrete themselves safe from discovery; when we can start from our homes to take a car for Boston, as we now start to take an elevated train, knowing that, if we miss one car, another will be soon at hand; when electric incandescent lamps, which can not, in case of accident, scatter burning oil in all directions, shall fill the car with a mild and steady light; when dispatches can be received on board a train in motion as well as at an office; when the cars shall be heated and meals prepared by electric stoves which can not, in case of accident, set fire to the car-all the electricity needed for these and numberless other purposes being derived from the same convenient source the conductor carrying the current which furnishes the propelling power?

case.

That any such ideas as to what electricity can accomplish are visionary and impracticable may seem to be the case to some; that they are so in reality is not believed by many who have given the subject impartial study. Some of these believe that, in the very near future, electric cars will supplant horse-cars; and upon short lines like elevated roads, steam-locomotives; but that it will not be practicable for many years to run electrical cars upon long lines. Such may be the But it should be remembered that, in most instances in the history of industrial progress, the practical developments of meritorious systems have surpassed in rapidity and extent the expectations of even impartial men. A very high scientific authority in England once spoke very favorably of the idea of using steam-vessels for accomplishing short distances, and for river navigation, but laughed heartily over the suggestion of their ever going to sea, and offered publicly to eat the boilers and engines of the first one that should cross the Atlantic. Probably there are not many men who, in the light of what has recently been accomplished, would promise to eat the motor of the first electric car that should run from New York to Chicago.

A

PHOTOGRAPHING A STREAK OF LIGHTNING.

BY GASTON TISSANDIER.

BOHEMIAN observer, M. Robert Haensel, of Reichenberg, has succeeded in accurately photographing a flash of lightning. His pictures, of which he has taken several, show the light of the flash, under the form of long, continuous sparks, traversing the atmosphere. With the spark the landscape also is well produced, and a means is

given for estimating the length of the luminous train, which, in one instance, is calculated to be seventeen hundred metres, or more than a mile.

Wheatstone demonstrated by direct experiments of great ingenuity that single flashes of lightning do not last more than a millionth of a second. We may judge from this of the wonderful sensibility of the new gelatine-bromide plates which permit the taking of correct views under these conditions.

M. Haensel has given a short account of the circumstances under which his photographs were taken and of the processes he employed. On the 6th of July, 1883, during a storm, when the sky was traversed

by frequent flashes of lightning, he turned his instrument at about ten o'clock in the evening toward that point whence the strongest flashes seemed to issue. The apparatus was furnished with the most sensitive gelatine-bromide plates, and the flash left its own impression upon them as it was formed. Out of ten plates that were exposed, he obtained only four photographs, of two of which we here give exact copies, taken from heliographic reproductions by M. Gillot, of Paris. The first figure represents two flashes. In the left one will be observed a double spark, which also appears triple in the middle. Simulta

VOL. XXIV.-48