CHAP. x. ] GA S-ENGINE8. 5 1 1 



for kindling the gaseous mixture in. each of the chambers of the 

 cylinder. For this purpose the wires of the induction coil end 

 respectively in i i on one of the metallic ends of the cylinder, which 

 they penetrate by an insulating rod of porcelain ; the spark flies from 

 the piston to this platinum wire. The explosive mixture which 

 enters the chamber at the same instant, owing to the motion of the 

 slide-valve, is successively kindled. The heat resulting from these 

 successive explosions is communicated to the air, and by expanding it 

 furnishes the motive force. At the same time the other slide-valve 

 lets the gas produced by the combustion, and which is now in the 

 other chamber, escape ; whence the alternating motion of the piston and 

 the motion of the shaft and fly-wheel. Since the sides of the cylinder 

 are heated at each explosion, and in order to avoid the high tempera- 

 ture which would often be the consequence, they are surrounded 

 by a case in which a current of cold water is continually circulating ; 

 this current arrives by the tube E and leaves by the tube e. 



' Hugon's engine chiefly differs, as we have said, from Lenoir's, by 

 the method of exploding the gaseous mixture. Instead of induction 

 sparks, a jet of gas is brought by the motion of the engine itself first 

 into contact with the mixture, and then away from it. 



In this respect Otto and Langen's gas-engine resembles Hugon's ; 

 but it differs from it as well as from Lenoir's in an essential point. 

 This engine, as improved by Crossley, works by the vacuum resulting 

 from the explosion of common coal gas and air ; the piston is not, as is 

 usual, connected with the shaft on both up and down stroke, but on 

 the down stroke only. It is thus at liberty to fly up freely from the 

 force of the explosion, which takes place at the bottom only, and by 

 driving the piston before it empties the cylinder of air through its 

 open upper end. The return of the air on the down stroke yields the 

 driving power, and turns the shaft by means of a friction clutch, to 

 which the piston is geared by the rack. The vacuum beneath the 

 piston is equal to about eleven Ibs. per square inch for the greater 

 part of the down stroke. The governor does not act, as is usual, by 

 increasing or decreasing the power of each stroke, but by varying the 

 number of strokes, each being of the same power. This is done 

 without materially changing the speed of the shaft. Three or four 

 explosions per minute are generally sufficient to turn the engine itself, 

 and as a maximum of thirty to thirty-five may be made there is a 



