or running on a down grade becomes a generator which is helping to supply the current needed to operate the remaining trains.

This method has already been shown to save about forty per cent as against any other electrical system.

Again, instead of the current being all supplied by the main generating station at one or two points, it is supplied from nearly as many moving stations as there are trains slowing down or running on down grades. With any given size of conductors and average potentials this would greatly reduce the loss, or, with the same percentage of loss on line, the main conductor would be very much smaller, because less current is supplied from the central station, and it is transmitted a shorter distance. The relative size of conductors necessary would be about as one hundred to forty-five, a saving of fifty-five per cent in favor of this system. In the Sprague system there would be required at the central station 100 × 2710 = 4520 H. P., something less than that developed on the present locomotives, which is 4650 H. P. That is, the losses of two conversions and one transmission is more than counterbalanced by the amount saved in this system of breaking.

The present engines have to use a good grade of coal, which costs, ready for use, $4.00 per ton. The duty of these engines is about six pounds of coal per horse-power per hour. Large stationary engines can be relied upon to develop horse-power per hour on three pounds of a lower grade of coal, such as a mixture of anthracite dust and bituminous coal, which can be delivered to the furnaces for $2.50 per ton. The ratio of expenditure for coal would be found as follows: 89:88 × 1:98 = 3.30; that is, for every $3.30 spent for coal in the present steam-plant, there would be expended $1.00 in the Sprague system, a saving of about seventy per cent. Against this, and some present labor expenses, must be put the cost of running the central stations.

Another consideration

- which must be taken into account when a part of the energy of the trains is returned to the lines, as I have described is the great saving in the original investment at the central stations as well as in the conductors. In the particular instance here given there is a difference in the power to be provided for at the central stations of 7382. 4520 =2862 H. P. The saving on this would, for lots, buildings, boilers, engines, dynamos, and fittings, be

not less than about $150 per H. P., or $429,000. There is nearly a proportional saving in the labor, depreciation, and the incidental expenses of the central station. Again, since the motor system affords a very perfect system of breaking, neither vacuum nor pressure brakes need be used, although the hand brakes would, of course, be retained. As a somewhat remarkable corroboration of theoretical by practical work, I would refer to the account of Mr. Angus Sinclair's work in the Scientific American (Supplement of October 3d). Through the courtesy of Col. Hain, Manager of the Manhattan Road, Mr. Sinclair, assisted by Mr. J. D. Campbell, general foreman of the Elevated Railroad machine-shops, made a very thorough test of the capacity and performance of one of the standard engines on regular duty. The engine was indicated for two round trips; that is, over a run of about thirty-four miles, and all other necessary data taken. The average power used during the whole distance was 77.8, ten per cent of which is allowed for friction of the engine, leaving net 70 H. P. This by actual experiment.

By theoretical determination I get 70.3 H. P., which includes five per cent friction, or a net of 67 H. P. The difference is 3 H. P., or 4 per cent, which may represent the excess of weight of the trains tested.

I have presented these facts about the present and future of the elevated roads of New York for your consideration, not because you are particularly interested in New York, but because the problem of rapid transit in Boston has become one of the urgent needs of the present. As the elevated roads there met with great opposition, so has the project of reaching the suburbs of Boston roused a host of objectors. The reasons for this are in part sound. Your streets are, many of them, narrow and crooked. Property owners along the route object to a double-track system of roads extending the full width of a street, to the noise, the steam, the water, the oil, the vibrations, the dirt and cinders incident to a steam system.

But the elevated roads of New York were projected some years ago. Active minds of engineers and inventors have worked out improved methods of construction for the special needs of cities like Boston, where trains may be required to go by one street and return by another. Such roads can be built, the structure of which will not take up as much room in the streets, and will not obstruct the air and

light over one-half as much, as the New York roads, and I feel confident they can be built for less money. With electric propulsion you can have rapid and smooth-running trains of one, two, or more car units. The strain on the structure being much less than in a steam-plant, the whole structure can be made lighter in the same proportion. Dust, smoke, cinders, oil, and water will disappear. Power will cost less. Trains can be run at shorter intervals, and under more perfect control. The energy of the train will become available for the purpose of braking. Repairs of superstructure will be less. In short, electric propulsion, more than any other thing, will make practicable for Boston what it has so long and so sadly needed, — rapid transit to its suburbs. I need hardly point out to you the increase in the value of this property which will more than pay the cost of the roads.

After some discussion the meeting closed with a vote of thanks to Lieut. Sprague for his very interesting paper.

MEETING 340.

The Pneumatic Dynamite Gun, and the Use of High Explosives in

Warfare.

BY LIEUT. E. L. ZALINSKI, U. S. A.

The 340th meeting of the SoCIETY OF ARTS was held at the Institute on Wednesday, Dec. 23rd, at 8 P. M., President Walker in the chair.

After the reading of the minutes of the previous meeting, and the election of new members, the President introduced Lieut. E. L. Zalinski, U. S. A., who read a paper on "The Pneumatic Dynamite Gun, and the Use of High Explosives in Warfare," illustrated with numerous views shown on the screen.

Lieut. ZALINSKI said: The first pneumatic gun presented for experiment by Mr. Mefford, the first designer, consisted substantially of a brass tube two inches in diameter, one-quarter inch thick, and

twenty-eight feet in length, placed in a T rail, stiffened by tie rods, and mounted on a tripod. (See Fig. 2.) It was arranged for breech loading. The tube was connected with an air reservoir by means of a flexible hose. Air was admitted from the reservoir by means of an ordinary cock worked by hand.

The projectiles were cylindrical brass tubes about one and one half inches in diameter, and from twelve to eighteen inches in length, with a wooden frustum of a cone attached, the larger end being the diameter of the bore. The points were wooden plugs, leaded to throw the center of gravity well forward. The results obtained were surprising. At a range of over eight hundred yards the missiles were driven into pine blocks from sixteen to twenty-four inches, and with less than five hundred pounds pressure shells were thrown twentyone hundred yards. The firing showed greater accuracy than ordinarily obtainable with smooth-bore guns.

Here was an extreme example of the most recent line of development in ballistics, i. e., slower powders giving much lower pressures, but burnt in longer bores, and thus imparting, eventually, higher velocities than previously obtainable.

The maximum length of powder guns is thirty-five caliber. This gun is one hundred and sixty-eight caliber long, and, in consequence of its greater proportional length, and the fact that the pressure is maintained throughout the whole length, while it falls rapidly in powder guns, an energy may be imparted to the projectile nearly approaching that of powder guns. This, too, without subjecting the projectile and its contained charge of explosive, if a shell, to any pressure that might produce premature explosion. A gun of fourinch diameter of bore, and forty feet long, was next built. The valve was automatic in its action. It was required to open rapidly, permit a certain uniform volume of air to escape, and close about the time of the arrival of the projectile near the muzzle of the tube. It might be considered either as a time-valve or an air-meter. The projectiles were made with the center of gravity as far forward as possible, as experiment has shown that, so constructed, they will be much steadier in their flight and the range more nearly uniform. In the first experiments ordinary percussion-fuses of fulminate, placed in the point of the conical head of the shell, were used to explode the charge, but they did not act uniformly, and many failed to work at all. Next,