which this heat has to reach the cooling water also increases; ( b ) that the weight per horse-power increases with the size of the cylinder; (c) that useless forces are called into play-useless in that they are either stationary and do no work or even produce negative work. These result from ( I ) the fluid pressure on the cylinder covers, which has to be transmitted through the framing of the engine; ( 2 ) the negative work of the compression stroke, which in single-acting engines produces a

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... eversal of twist in the crankshaft; and (3) the inertia forces resulting from want of balance, and imperfect cushioning. The Fullagar internal combustion engine eliminates these factors, and has besides the advantages of mechanical simplicity and accessibility. The construction, which is shown diagrammatically in Figs. I and 2 , consists in using as a unit two open-ended cylinders side by side, each with two pistons, and rigidly connecting the FIG. 1 FIG. 2 pistons A to D, and C to B, by means of pairs of oblique rods, external to the cylinders. The action of the engine is as follows: An explosion taking place between A and B drives B down and A up, drawing up D by the oblique rods, and giving, through the two connecting-rods, two equal and opposite impulses to the two cranks. The side thrust produced by the oblique pull is, of course, taken by the crossheads of A and D, which are provided with suitable guides for the purpose. The obliquity of the rods is small, less than the maximum obliquity of the connecting-rods, so that the friction is actually less than would be the case if each piston had its own crank and connecting-rod and the mechanical efficiency of the engine is high. At the ends of their strokes the pistons uncover inlet and exhaust ports in the cylinder walls, as in the Oechelhauser arrangement. The engine works on the two-stroke cycle, and each crank receives, therefore, two impulses per revolution. Air is supplied