while air during compression opposes a force increasing towards the end of the stroke; thus the power rapidly falls off as the resistance increases, causing a perceptible reduction in speed at the end of each stroke. If such a machine could be run at high speed, the weight (or more correctly, the mass) of the pistons and connections would, by inertia, help out the decreasing steam pressure when slowing to pass the centers, and thus produce a more even effort on the crank; but sufficiently high speeds are not possible for the automatic-lift valves generally used on small compressors. The varying power and resistance can be very satisfactorily balanced by connecting steam and compressing pistons to separate cranks set at right angles. Having provided two frames and cranks, a slight additional outlay will supply an extra pair of cylinders tandem to the first pair, making a full duplex compressor. The excess steam pressure at the commence

ment of the stroke of one side is here transmitted by the crank shaft to the other side of the machine, to help out the deficient pressure of the expanded steam when the stroke is nearly finished. Such a machine has no "dead centers," and can be run at very slow speed when necessary.

As it is generally desirable to maintain a constant air pressure, and to vary the speed of the machine according to the quantity of air required, speed governors for the steam cylinders are not needed except to prevent racing in case of a bursting pipe or other excessive discharge of air. Some form of adjustable cut-off valves is very desirable in order to allow of suiting the work of the steam cylinder to the load. The pressure is controlled by automatic devices actuated by the rise and fall of the air pressure, either shutting off the air intake, opening a by-pass around the compressor piston, or (in case of duplex machines which can start from rest without attention) shutting off steam and stopping the machine.

A description of the standard types of commercial compressors would be incomplete without reference to the most remarkably wasteful "steam eater" known to the compressor trade-a machine using ten times as much steam as would be necessary for pumping the same amount of air by means of a fairly eco

nomical compressor, and yet a device most ingenious and entirely satisfactory for its work. This is the air-brake pump, which, for actual conditions of train service-where it stands idle until the closing of the throttle and the application of brakes leave a large and heavily fired steam boiler to blow off at the safety valve until the fire can be checked-is seen to be well adapted. Indicator cards show that the entering steam is throttled through about half the stroke, while the exhaust is similarly choked at first and only let out freely about the time of full opening of the valve. The result is a "straight-line" compressor having no crank or fly wheel, with nothing moving but its two pistons and one rod, and yet so perfectly balanced between effort and

resistance that its strokes are smoothly made at any speed from slowest to fastest, and all with maximum simplicity and minimum weight. These machines are also built with compound steam and twostage air cylinders, and in these cases have pressures in the cylinders so nearly uniform that the steam distribution may be considerably more economical than it is possible to obtain in the single-stage compressor.

The selection of general types and special details for compressors must be based, as in all other cases of machine design, on the practical condition of getting the best return from the money invested, with due regard to the importance of reliability and durability in each [r ticular case.

motive which can draw six or eight cars over a well-built track at the rate of seventy or eighty miles an hour; but the problem of reducing the amount of fuel consumed, and of lessening the strain on the rails caused by the vertical shock of the rotating weights in the driving wheels, without sacrificing either speed or power, has proved much more difficult.

Of the many attempts made to solve this difficulty, undoubtedly one of the most successful so far has been that of S. M. Vauclain, who two years ago designed a locomotive to which the name of the Vauclain Balanced-Compound was given. Since then, several of these engines have been built by the Baldwin Locomotive Works, and have been used

tives, whether single-expansion or compound, and in four-cylinder types such as the tandem and the original Vauclain compound, the reciprocating parts are counterbalanced by rotating weights in the driving wheels. This arrangement of balance becomes unsatisfactory, particularly for heavy locomotives and in cases where extremely high speeds are attained. By balancing their reciprocating parts against one another, the rotating balance in the wheels used to complement these parts can be eliminated, avoiding to a great extent the vertical shocks, and reducing the strain upon the track to that directly due to the weight of the locomotive. Consequently, with a self-balanced arrangement of reciprocating parts, the weight on the driving

wheels may be increased without damaging the track, and higher speed is attainable without undue strain upon the working parts of the locomotive. The balanced-compound engine is intended to accomplish these results, and to simplify, as far as possible, the arrangement of the working parts.

STEAM DISTRIBUTION IN BALANCED-COMPOUND CYLINDER.

The cylinders are a development of the original Vauclain four-cylinder compound type, with one piston slide-valve common to each pair. Instead of being superimposed and located outside of the locomotive frames, the cylinders are placed horizontally in line with one another, the low-pressure outside and the high-pressure inside the frames. The slide-valves are of the piston type, placed above and between the two cylinders which they are arranged to control. A separate set of guides and connections is required for each cylinder. The two high-pressure cylinders being placed inside the frames, the pistons are necessarily coupled to a crank axle. The lowpressure pistons are coupled to crank pins on the outside of the driving wheels. The cranks on the axle are set at 90 degrees with each other, and at 180 degrees

with the corresponding crank pins in the wheels. The pistons, therefore. travel in the opposite direction; and the reciprocating parts act against and balance one another to the extent of their corresponding weight.

The distribution of steam is shown in the accompanying diagram. The live steam port in this design is centrally located between the induction parts of the high-pressure cylinder. Steam enters the high-pressure cylinder through the steam port and the central external cavity in the valve. The exhaust from the high-pressure cylinder takes place through the opposite steam port to the interior of the valve, which acts as a receiver. The outer edges of the valves control the admission of steam to the low-pressure cylinder. The steam passes from the front of the high-pressure cylinder, through the valve, to the front of the low-pressure cylinder, or from the back of the high-pressure to the back of the low-pressure cylinder. The exhaust 'from the low-pressure cylinder takes place through the external cavities under the front and back portions of the valve, which communicates with the final exhaust port. The starting valve connects the two live steam ports of the high-pressure cylinder, to allow the steam to pass over the piston.

The dimensions of the high-pressure cylinder are 15 by 26 inches; and of the low-pressure, 25 by 26 inches. The working pressure is 200 lbs. The fire-box has a heating surface of 168.5 square feet: and the grate, one of 34.69 square feet. The rigid wheel-base is 13 feet 6 inches, and the total length of the engine 27 feet 5 inches. The total weight of the locomotive is 160,000 lbs. Its water capacity is 5.500 gallons, and the tender holds 10.5 tons of coal.

As an illustration of the superiority of the new Vauclain engine over other types in common use, two recent trial runs may be cited. These took place on the line of the Chicago, Burlington & Quincy from McCook to Akron, Col., a distance of 143 miles, including an elevation of 2,150 feet. A Vauclain balancedcompound locomotive drew the mail train of ten cars weighing 664 tons these 143 miles in 2 hours 56 minutes, at an aver

age speed of 48.6 miles an hour, reaching at times a velocity of 68 miles an hour. The usual time made by the mail train drawn by single-expansion locomotives from 17,000 to 35,000 lbs. heavier than the Vauclain, was 3 hours 36 minutes. On a second run over the same division with a train of twelve cars, the Vauclain made an average speed of 42.46 miles an hour, which was thirteen minutes faster than the heavier locomotive carrying only eight cars could make. On these trials the Vauclain engine burned, each trip, 32 per cent less coal and used 20 per cent less water than the others.

The managements of several of the large Western roads have been quick to perceive the great advantage of the new locomotive; and nearly 100 of them are now in use on the tracks of the Burlington, Santa Fé, and other systems. In the East, the New York, New Haven & Hartford Railroad is the only road thus far to adopt the new engine. They have ordered twenty, two of which have been received and are already in daily opera

tion. On the trial trip between New Haven and Boston, November 12, 1904, a new Vauclain locomotive broke the record by 19 minutes, making the run of 160 miles, including three stops, in 2 hours 55 minutes. It is not unreasonable to prophesy that when the railway company shall have completed its new bridges at Coscob, Bridgeport, and Westport, it will be possible to make the run from New York to Boston in a little over four hours, representing a saving of from 40 to 50 minutes over the fastest time now made by the special limited expresses. One of the new Vauclain engines could, if necessary, haul the train the entire distance without having to re-coal on the way.

It may be gathered, then, from the facts thus briefly set forth, that the Vauclain balanced - compound locomotive seems destined to work a revolution along the lines of freight and passenger traffic by increasing greatly the speed and power of locomotion, as well as very appreciably lessening the expense for fuel and maintenance of track.