4

THE DISC ENGINE.

covers are frustums of hollow cones, of such an angle that the apex of eachcone would not reach the centre of the spherical chamber. In the smallends of these conical frustums spherical seats are bored, having the same centreas the spherical chamber.

At the bottom between the two covers or ‘ cones, ’ and at right angleswith them, i. e. longitudinally with the cylinder, is fixed a thick plate or‘partition,’ which is let into grooves in the cones and in the cylinder, theupper edge being fitted with metallic packing curved to the same radius andfrom the same centre as the spherical seats in the cones.

The piston or ‘ disc ’ consists of a circular plate of such thickness thatthe two flat sides will respectively touch the two cones. This disc is eithercast with or attached to a spherical boss or ‘ ball ’ concentric with it, whichball fits the spherical seat in the cones and partition. A piece is cut out of thedisc to allow the partition to pass through it. The periphery of the disc isfitted with metallic packing rings, much in the same way as the pistons ofother engines. Also the seats in the cones are fitted with metallic glands, tocarry the ball of the disc, and with hemp packing to render the seat steam-tight.

In the ball or boss of the disc is keyed an arm or ‘ diagonal shaft ’passing through the ends of the cones: one end of this arm enters a brassbush or block fitted in a crank or pulley fixed on the screw-propeller shaft, towhich it gives motion ; the steam causing the disc to roll on and between thetwo cones, and consequently the end of the diagonal shaft to describe a circle.The only parts, however, which revolve, are the crank and the screw-shaft, thedisc being prevented from rotating by the partition.

The steam ports are on one side of the partition, and the exhaust port onthe other side, and the engine works at full pressure without any valves what-ever, the disc itself shutting off the steam from the induction and admitting itto the eduction port. Expansion valves are, however, now generally used withthis engine, which offers admirable facilities for their use.

The advantages gained by the use of this engine to drive the screw-pro-peller are as follows:

The disc engine acts with a uniform force on the crank of the propellershaft continuously in the direction of the motion of the crank, and having nodead points nor a reciprocating motion, the engine runs with ease at the samespeed as the propeller.

The engine is lighter and occupies less space than the ordinary engines, andthe consumption of fuel has been proved by numerous experiments to be less.It is also much less liable to derangement, for no water can get jambed in the