332 THE POPULAR SCIENCE MONTHLY. 



ton fitting the cylinder tightly, a plunger moving in it loosely, and the 

 system of cranks and connecting-rods by which the motion of these 

 parts is communicated. The upper portion of the cylinder, through 

 which the tightly fitting piston alone moves, is water-jacketed, and 

 consequently remains cool, while the part below this becomes more 

 or less highly heated. In this heated portion the plunger moves, al- 

 ternately displacing the air from above the fire. It is a long iron shell 

 filled with wool or other non-conductor, and provided with studs on 

 its sides which keep it from the walls of the cylinder. The machine 

 is started by giving a few turns to the fly-wheel, when it begins run- 

 ning of itself, the action being as follows : 



The plunger being raised, the air below it is heated and expands, 

 forcing the piston upward. As it does this, the plunger is brought 

 down with a quick motion, displacing the air, which passes through 

 the annular space between the plunger and cylinder wall to the upper 

 part of the cylinder. Here it comes in contact with the cool surface 

 of the water-jacketed portion and contracts, forming a partial vacuum 

 below the piston, w^hich then descends by atmospheric pressure. By 

 the upward movement of the plunger, the air is again brought in con- 

 tact with the heated bottom and sides of the cylinder, and the same 

 operation is repeated. The plunger-rod passes up through the piston, 

 and by means of the simple system of connecting-rods and cranks 

 shown in the figure the proper motion is given the plunger. The pump 

 is placed at the side of the cylinder, and its rod connected directly to 

 the beam of the engine. The water is drawn into the pump and dis- 

 charged through the water-jacket, the slight heating of the water in 

 its passage through the jacket being no disadvantage, while the con- 

 tinual passage of fresh water readily keeps the cylinder cool. The 

 engines have so far only been made for pumping purposes, but they 

 can readily be adapted to those of a small power, by using only a part 

 of the power of the engine in pumping. Four sizes of the motor are 

 made, three with single cylinders, six, eight, and twelve inches in 

 diameter, and one with two cylinders of the latter size. The first lifts 

 two hundred gallons of water fifty feet per hour, with an expenditure 

 of fifteen feet of gas, the second three hundred and fifty, the third 

 eight, and the fourth sixteen hundred gallons, the same height, with a 

 proportional consumption of fuel. The prices vary from two hun- 

 dred and ten dollars for the smaller to five hundred and fifty dollars 

 for the largest size. Only the two smaller sizes are at present made 

 to burn gas. They are perfectly safe, so simple that they can be used 

 by the most inexperienced persons, and for their special purpose are 

 probably as cheap and satisfactory machines as can be made. 



Another engine, and one of the most serviceable of this- class of 

 machines to be found in the market, is the Rider compression engine. 

 Like the other hot-air engines, it is constructed chiefly with a view 

 to pumping, but when desired for power in addition it may be ob- 



