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In this engine a free piston was used in a vertical cylinder, the former being thrown up by the force of the explosion. The only work done on the up-stroke was that to overcome the weight of the piston and piston rod, and the latter being made in the form of a rack, engaged with a toothed wheel on the axle as the piston descended, causing the fly-wheel and pulley to rotate.

The piston rods have strong nuts on each side of each of these arms to attach them to the arms, and also to enable the length of the piston rods to be suitably adjusted, to leave equal clearance between the piston and each end of the cylinder at the termination of the stroke. CROSS HEAD AND PUMP ARMS. Messrs. Q. Will you recapitulate the main particulars of the air pump?

Let O be the center of the shaft; let L O M represent the face of the main valve seat, in which is shown the port leading to the cylinder; and let A be the edge of the main valve, at the beginning of a stroke of the piston.

In the steam-engine the piston is forced backward and forward by the expansive power of the steam, the vapour being admitted alternately to the forward and rear ends of the cylinder.

In side lever engines it is a judicious practice to add a nut to the top of the piston rod, in addition to the cutter for securing the piston rod to the cross head. In a good example of an engine thus provided, the piston rod is 7 in. in diameter, and the screw 5 in.; the part of the rod which fits into the cross head eye is 1 ft. 5-1/2 in. long, and tapers from 6-1/2 in. to 6-13/16 in. diameter.

Thousands of feet above us the mighty cylinder uprose, and in the lessened circle that was its mouth I glimpsed the bright stars; and knew by this it opened into the free air. All of half a mile in diameter was this shaft, and ringed regularly along its height by wide amethystine bands like rings of a hollow piston.

Matheson, one foot caught under a seat, was dragged down and down until his heart hammered like a piston and his lungs were bursting with the fierce effort to hold his breath. To the drowning man there comes a moment when he perforce gives up the fight and abandons himself to the blessed peace of unconsciousness, like a wanderer in a snowstorm lying down to rest.

C.A. Parsons, the inventor of the engine, worked out the idea that inventors have been studying for a long time since 1629, in fact that is, the rotary principle, or the rolling movement without the up-and-down driving mechanism of the piston. The Turbina was driven by a number of steam-turbines that worked a good deal like the water-turbines that use the power of Niagara.

Under 50 lbs. of steam it develops sufficient power to run a small electric-lighting installation, or to do other useful work on a moderate scale. Piston, 1-1/2 inches diameter; 1/2 inch long. Stroke of piston, 2-1/4 inches. Connecting rod, 5 inches long between centres; 5/16 inch diameter. Piston rod, 5-1/8 inches long; 1/4 inch diameter. Valve rod, 4-1/8 inches long; 3/16 inch diameter.

The cone of the piston rod, by which it is attached to the piston, is turned the reverse way to that which is adopted in common engines, with the view of making the cutter more accessible from the bottom of the cylinder, which is made to come off like a door.