336 THE POPULAR SCIENCE MONTHLY. 



of using the heated air in moving the piston differs somewhat from 

 that employed in the engines above described, being more nearly like 

 that in which steam is used in the steam-engine. The furnace is air- 

 tight, the air di-awn from the atmosphere being forced through and 

 over the lire, and the exj^anded air and products of combustion being 

 admitted to the cylinder through valves worked by the engine in a way 

 entirely similar to the admission of steam in the steam-engine. The 

 cylinder is placed over the furnace, from which it is separated by a par- 

 tition of iron faced with fire-brick upon the furnace-side. This furnace 

 is lined with fire-brick upon all sides except the bottom, making a very 

 durable construction, as there is nothing exposed to the direct action of 

 the fire, to burn out. The air is drawn from the atmosphere by the up- 

 ward movement of the piston in the small cylinder at the left, through 

 the valve B, and on the down-stroke of this piston is forced through the 

 channel G into the furnace. The valves H and E regulate the amount 

 passed over and through the fire. The heated air and products of 

 combustion are admitted into and exhausted from the cylinder through 

 the puppet-valves, shown in the chamber to the right of the engine. 

 A steady gradually diminishing pressure is exerted against the piston 

 by these heated gases, and drive it to the upper end of the cylinder. 

 The exhaust-valve then being opened by the mechanism of the engine, 

 the piston descends by atmospheric pressure, forcing the gases out into 

 the air. While the power-piston is making its doAvnward stroke the 

 supply-piston draws in a fresh charge of air, which is forced into the 

 furnace during the up-sti'oke. A fly-wheel makes the motion of the en- 

 gine smooth and uniform. The power-piston consists of two shells, 

 the upper one turned true to fit the bored portion of the cylinder, and 

 the lower one fitting it loosely. This latter protects the first portion 

 from direct contact with the heated gases, and, as the upper part of 

 the cylinder does not become overheated, a water-jacket is not needed. 

 As the furnace is a closed compartment, the engine must be stopped in 

 order to replenish the fire. This is not so much of an inconvenience, 

 however, as it would at first sight appear, as one firing in the morning 

 and another at noon, when the motor is running continuously ten hours 

 a day, are all that are required. The machine is compactly built, and 

 runs with very little noise. It is made in sizes of from one and a half 

 to seven horse-power, at prices ranging from something less than five 

 hundred to one thousand dollars. According to the statement of the 

 manufacturers, the engine is exceedingly economical of fuel, the one- 

 and-a-half horse-power using but forty pounds of coal per day of ten 

 hours, and the three-and-a-half, eighty pounds. This is but a little 

 over two pounds per horse-power per hour, a result attained in the 

 steam-engine only in the larger-sized and most perfectly constructed 

 machines. 



