The diagram, which forms part of the illustration, will serve to. explain the theory of the dynamometer,

It is established in the transmission of force by a belt, that the force exerted is the difference of strain on the two sides of the belt, multiplied. by the velocity of movement of the belt itself. A belt, in its initial state, when at rest, is a continuous band, subject to a uniform strain in. all its periphery, bringing into action the elasticity of the band and of the shafting or pulleys to sustain this strain. And the same equality of strain exists when the belt is running without the performance of work. [It being supposed that such running is devoid of resistance from friction or other cause.] But as one of the pulleys presents a resistance to being turned, and the other, impelled by some motor through its shaft, takes up and overcomes this resistance through the belt, the adhesion of the belt to the pulleys is now brought into action,. and one side of the belt is abnormally tightened, while the other side becomes correspondently loose, and the difference of strain between. the two sides becomes the measure of the force transmitted at some given velocity.

In the arrangement of pulleys and belt shown by the side elevation (see plate), it is obvious (the weight of the carrier pulleys, the framesupporting the same, and of the belt, being balanced) that when at rest or running with no resistance the system will come into equilibrium. with equal but opposite angles for both the upper and lower belt. The indicator, attached to the carrier frame, will then be in the straight line between the centre of the main pulleys, and will coincide with the pointer attached to the permanent framework, which is placed also in the same line. If the belt in this position be subject to some normal strain, it is evident that a definite proportion of this strain will be exerted. equally upon the axes of the carrying pulleys. If now the system be put at work, the belt will come at once to have a tight side and a looseside, and the difference of strain can be measured by the load necessary to preserve the carriers in the same position as regards the line between the centres of the main pulleys.

The resultant of strain from the deflected band varies as the sine of the angle, and to make this instrument as simple as possible the angle of the belt has been taken as such that its sine =

tension of belt on tight side.

[Sin.

force transmittel.

weight; T2 =

If, therefore, a certain force, W, is needed to preserve the central position of the indicator, there will have been transmitted by the belt a force = 2 W.

Accepting these relations of angles and force, the relative positions of an arrangement which shall employ pulleys 24 inches in diameter for the main pulleys, and others 8 inches in diameter for the carrier pulleys, is given by the diagram, when the length of inclined belt is taken at 36 inches. An allowance of inch has been made for half the thickness of the belt when the radii of the line of the belt on the two pulleys become 121 and 816, respectively. It will be easy for any one to compute the triangle and verify the dimensions on the diagram.

The machine itself consists of a bed framing of wood, joint-bolted 'together, upon which is mounted a high table, also joint-bolted throughout. The bed frame carries two pairs of inverted hangers, 24-inch shaft, 20-inch drop, with self-oiling boxes. Each pair of hangers carry shafts 27 inches of diameter, with two pulleys, 24 × 7 inches, high. One of the pairs of hangers have brackets cast upon them, which form the fulcrum for the carrier frame. The carrier frame has two pulleys, 16 × 7 inches, high, and the pulley end of the frame is suspended by knife-edge pins and links to a scale beam, the P of which has half the usual weight.

With this P the scale indicates the strain transmitted by the belt without computation. The suspension frame, also, is hung by wellfitted pins and links to a counterbalance system of levers and weights, with a dash pot attachment to control the action of the dynamometer against sudden variations of work.

This dynamometer, with the proportions given, and on the supposition that 6-inch belts be used, will transfer, where the belt is strained normally upon both sides to 404 pounds per inch of width, 72 horsepower. As, however, the contact with the driving or driven pulleys can scarcely be so great as that on the main pulleys, where 210° exists, it is probable that this particular instrument cannot be held to measure the transmission of much more than 6 horse-power. When the unbalanced strain of the two sides of the belt must amount to 47·4 pounds per inch of width, while the actual maximum strain on the tight side of the belt cannot be less 56 to 60 pounds, and may much exceed that value if the normal strain rises above 40 or 42 pounds.

HIGH RAILWAY SPEEDS.

By W. BARNET LE VAN.

Read before the Franklin Institute, at its meetings, May 19th and June 15th, 1880.

Railways being now the common highways of our country, their managers naturally seek all means of accommodating and meeting the wants of the traveling community.

The active rivalry now existing between the Pennsylvania Railroad and the Bound Brook Route of the Philadelphia and Reading Railroad has resulted in giving us the most improved facilities for communication between the two principal cities of this country, and has placed our railway speed on a par with the fast time of the British. express trains.

It is but a few years ago that a trip to New York and back in the same day was considered a wonderful achievement; the time occupied, being three hours each way, was thought very short, whereas to-day one can have his breakfast and go to New York, transact business and return and dine in his own house. But even the great reduction of time has not been considered sufficient to comply with the requests of rapid transit, and the two roads referred to are contemplating and preparing to run the 90 miles between Philadelphia and New York in 90 minutes.

Sixty miles an hour, as it strikes the ear, does not seem an impossibility, but if we look at it in all its bearings, and consider that it means one mile in one minute, or 60 miles in 60 consecutive minutes, it begins to assume proportions that seem insurmountable.

Some of the earliest locomotives ever built have run over a mile a minute, and in one instance a speed of 93 miles per hour was main-tained for a few miles.

To illustrate more clearly the difficulties in running sixty miles in sixty minutes, the locomotive must be capable at all times of developing seventy miles per hour, so as to meet any contingency that may arise. A locomotive at seventy miles an hour passes over one hundred and

two feet per second (70x2

15

=

102-6). Two objects near a person,

say three feet apart, pass his eye in the thirty-fifth part of a second..

When two trains having this speed pass each other, the relative velocity will be two hundred and five feet per second; and if one of the trains were one hundred and two feet long, it would flash by in a single second. To accomplish this, supposing the driving wheels to be six and one-half feet in diameter, and the piston to change its direction in the cylinder ten times in a second, there being two cylinders to every locomotive, and the eccentrics being so adjusted that the exhaust. steam discharges alternately, there are twenty discharges of steam per second, at equal intervals, and these twenty exhausts divide a second into twenty equal parts, each puff having a twentieth of a second between it and that which precedes and follows it. The ear, like the eye, is limited in the rapidity of its sensations; and, sensitive as those organs are, they are not capable of distinguishing sounds which succeed each other at intervals as short as the twentieth part of a second.

Therefore, to run sixty miles in sixty minutes continuously, and with a reasonable degree of safety, some modification in the form of engine as now built must be made. The road bed must also be in the best condition attainable, and as straight as possible, and if curves are indispensable they should not be less than 2000 feet radius.

Locomotives are distinguished as single or coupled, independently of their kind or class. When only a single pair of driving wheels is employed, the engine is said to be a single engine. When two or more pairs of driving wheels are used, connected by coupling rods, the engine is said to be coupled.

When six coupled wheels and a swing "pony truck" in front, connected by equalizing beams with the leading pair of coupled wheels, it is called Mogul, and when eight coupled wheels and "pony truck" it is called Consolidation.

To accomplish sixty miles in sixty minutes, the Baldwin Locomotive Works, of this city, have just placed on the Bound Brook route between this city and New York a new single engine, similar to those used on the fast lines in England, having but one pair of driving wheels, 6 feet in diameter. The ordinary driving wheels of passenger engines in this country do not exceed 53 feet, and two pair coupled together, are used. For fast speeds, with coupled driving wheels, as in ordinary use, the momentum of the parallel rods which connect the driving wheels becomes enormous, and is a source of great danger. Within a month past the parallel rod of an engine on the Pennsyl