442 ARCHITECHNICS. 



the joints, or limbs, are nearly straightened, as at the close of the 

 stroke in pulling at an oar. An ordinary man is said to be capable 

 of raising 6000 Ibs. at the rate of one foot per minute, during 8 

 hours per day. The measure of a horse's power, according to Mr. 

 Watt, is, that he can raise 33,000 Ibs. at the rate of one foot per 

 minute, during 8 hours per day. 



4. The application of Steam Power, depends on principles of 

 mechanics and calorics, to which we have already referred ; and it 

 now remains to describe the steam engine. The boiler, for generat- 

 ing steam, is usually made of sheet iron, in a cylindrical form ; and 

 with its gauges and safety valve, is rather a necessary appendage to 

 the engine, than a part of the engine itself. The steam from the 

 boiler, flows through the steam pipe, when the supply valve or throttle 

 valve is opened, into one end of the cylinder; where it acts upon the 

 piston, and presses it to the opposite end of the cylinder ; from which 

 part the previous steam, or air, is allowed to escape. The steam being 

 then admitted into this end of the cylinder, and let off from the other, 

 drives back the piston, and thus causes it to move alternately forward, 

 and backward, in the cylinder. The admission, and escape of the 

 steam, is regulated by means of the steam, and exhausting valves ; 

 which are so connected, by rods, or levers, with other moving parts, 

 that they are mechanically opened, and shut, at the proper time. 

 The piston rod, connecting the piston with the working beam, or 

 with the crank rod, transmits the motion to the axle, in order to 

 produce circular motion, either directly, or by means of the working 

 beam. 



In some high pressure engines, especially for locomotives, the 

 steam is let off into the air, or goes to create a draught through the 

 fire : and in such engines, the motion of the piston is constantly 

 resisted by the atmospheric pressure ; but in the Watts, or condens- 

 ing engine, the steam escapes into a condenser, or separate cylinder, 

 kept cold by an influx of cold water, through the condensing valve ; 

 by means of which, the steam is almost immediately condensed, and 

 its pressure on one side of the piston, in a great measure removed. 

 The water resulting from this condensation, is exhausted from the 

 cylinder, by the air pump ; and thrown into what is called the hot 

 well. This hot water is carried back to the boiler, by means of the 

 hot toater pump ; and the condenser stands in what is called the 

 cold well, supplied by what is termed the cold water pump, to assist 

 in keeping it cool. The rotary motion of the axle, is equalized, 

 where this is desirable, by means of a heavy fly wheel ; the mo- 

 mentum of which keeps up the motion at the dead points of the 

 crank: and the velocity may be regulated by means of a governor, 

 consisting of heavy balls suspended from levers, on each side of a 

 vertical axis ; and which, by flying off farther from the axle, if the 

 velocity be increased, act on other levers, which at once diminish the 

 supply of steam. 



