piston-rod from pressing against the side of the packing-box. This arrangement is called Watt's parallel motion.

The connecting rod, I, which transmits the motion of the workingbeam to the crank arm, K, and through it imparts a motion of rotation to the shaft of the engine.

The fly-wheel, V, which obviates to a certain extent the irregularities of motion in the engine.

The excentric, e, which, acting like a crank, produces a backward and forward motion in the connecting rod, Z. This rod acting on

the bent lever, Y, causes the rod m, of the sliding valve, to move up and down.

The cold-water pump, R, worked by the rod, H, which draws cold water from a reservoir, and forces it through the pipe, T, into the condenser. This pipe, terminating within the condenser in a rose, delivers the water in the form of a shower, and condenses the

steam.

The air-pump, M, worked by the rod, F, which draws the hot water and the air that is mixed with it from the condenser, and forces it into the hot well, N.

The feed-pump, Q, worked by the rod, G, which draws the water from the hot well and forces it into the boiler.

To explain the action of the engine, let the position of the parts be as represented in the figure. The steam entering the steamchest finds the upper passage open, and flowing through it, acts upon the upper face of the piston and drives it to the bottom of the cylinder. The steam below the piston meanwhile flows through the lower passage, and entering the eduction pipe at a, is conveyed to the condenser, where it is condensed. When the piston reaches the bottom of the cylinder, the excentric acts upon the bent lever to open the lower and close the upper passage. The steam from the steam-chest now flows through the lower passage, and acting upon the lower face of the piston, forces it to the top of the cylinder. Meantime the steam above the piston, flowing down the upper passage, enters the eduction pipe and is conveyed to the condenser. When the piston reaches the top of the cylinder, the excentric again acts to change the position of the sliding valve, and thus the motion of the piston is continued indefinitely.

The Locomotive.

477. The figure represents a section of a locomotive, the principal parts of which are the following:

The boiler, BB, with its flues, pp, and safety-valve, M. The dotted line represents the height of the water in the boiler.

The fire-box, A, communicating with the smoke-box, C, by means of the flues, pp. The fire-box has a double wall, the interval being

Explain the action of a condensing engine. (477.) Explain the principal parts of a locomotive engine.

filled with water and communicating with the boiler. E is the grate, and D the door for the supply of fuel.

The steam-pipe, SS, conveys the steam from the steam-dome to the steam-chest. It may be closed by a valve, V, worked by a

lever, L.

The steam-dome is an elevated portion of the boiler, the object of which is to permit the steam to enter the steam-pipe without any admixture of water, as might be the case were the steam taken from a lower level.

The cylinder, the piston, P, and the piston-rod, R, are similar to the corresponding parts of the condensing engine.

The blast pipe, L, through which the steam is blown off after having acted upon the piston, terminates in the smoke-box, and the blast of steam from it serves to increase the draft of air through the flues, and thus promotes the combustion of fuel.

The connecting rod, G, transmits the motion of the piston to the crank arm, by means of which a rotary motion is imparted to the driving wheels of the locomotive.

The manner in which steam acts to impart motion to the piston is the same as in the engine already described.

The Hydraulic Ram.

478. The HYDRAULIC RAM is a machine for raising water by means of shocks, caused by sudden stoppages of a stream of water. It consists of a reservoir, B, with a supply pipe, A, and an orifice, D, which may be closed by a spherical valve. Attached to the reservoir is an air-vessel, G, with a valve, E, and a

delivery pipe, II.

The stream of water entering the reservoir through the supply pipe, forces the valve D into its place, and closes the orifice. The sudden stoppage of the water causes a shock which forces a portion of water into the airvessel through the opening, E. The equilibrium being restored, the valve D

Fig. 835.

G

B

falls, as does the valve E, and immediately a second shock ensues,

Explain the action of a locomotive engine. (478.) What is the hydraulic ram↓ Explain its construction and use.

and a second supply of water is forced into the air-vessel, and so on indefinitely. The water forced into the air-vessel compresses the air in the upper portion of it, until its elastic force becomes sufficient to force a jet of water up the delivery pipe. The delivery once commenced will continue as long as the machine remains in order. Only a small portion of the water which enters the reservoir is raised into the delivery pipe.