OQ 



that's it; 



When it is desired to retain 

 steam, and to obtain a greater 

 degree of heat than is indicated 

 by 212° of Fahrenheit's thermome- 

 ter,* it is necessary to use 

 stronger vessels, 4, made of stouter 

 metal, 

 and with 

 fasten- 

 ings to se- 

 cure the 

 moveable 

 parts. 

 But even 

 these 

 vessels 

 would 

 burst, if 

 372. an outlet 



were not provided at a point 

 when the force of the steam be- 

 came nearly equal to the strength 

 of the vessel : because the force of 

 steam augments with increase of 

 temperature. Steam at the tern- 

 perature 212° presses with a force 

 of 151bs. to the square inch ; at 

 250°, 301bs. to the square inch ; 

 at 275°, 451bs. to the inch ; and 

 at lower and higher temperatures 

 the pressure, or force of steam 

 bears proportion to the heat im- 

 parted to it. 



Water in an open vessel will 

 not rise to a greater temperature 

 than 212°, because the steam 

 which flies away bears with it 

 the heat which, if confined, would 

 raise the temperature, and im- 

 part to the steam a greater force. 



The pressure of the atmosphere 

 upon everything at the earth's 

 surface is equal to a little less than 

 151bs. to the square inch. The 



» The thermometer is an instrument used to register 

 degrees of heat, it will be explained her ea.> t«r . 



reason that steam escapes at 

 212° is, that at that temperature 

 it exerts a force a little greater 

 than that of the pressure of the 

 atmosphere. Whenever steam is 

 confined, it acquires a higher 

 temperature, and consequently a 

 greater tendency to expand. 



The steam engine is simply a 

 mechanical contrivance to confine 

 steam, and give direction to its 

 increased force. 



Long before the steam engine 

 was invented, the expansive force 

 of steam was observed, and a toy 

 constructed, in which a jet oj 

 steam escaping from the mouth 

 of a figure turned a wheel, 5. A 



similar toy is made now. But 

 in this contrivance there was no 

 increase of force by confinement 

 and greater heat. Motion was 

 produced by the jet of steam 

 simply striking upon the fans of 

 the wheel. 



A simple instrument, 6, will 

 explain the first principle of the 

 steam engine. A glass tube, con- 

 taining a drop of water, 8, and 

 fitted with a moveable piston, 9, 

 being set over a flame, the water, 



will become steam, but will bo 



