QUALITIES OF THE STEAM-ENGINE. 269 



is too slow, the balls approach the axis, and open the 

 Talve. 



In high-pressure engines, the steam is not condensed, 

 but escapes into the open air at every stroke of the piston, 

 which produces the loud, successive pwjfoi of all engines 

 of this kind. 



The steam-engine, in its most perfect form, is a striking 

 example of human ingenuity, and its qualities are thus 

 described by Dr. Arnott: "It regulates with perfect ac- 

 curacy and uniformity the number of its strokes in a given 

 time, and records them as a clock does the beats of its 

 pendulum. It regulates the quantity of steam ; the brisk- 

 ness of the fire ; the supply of water to the boiler ; the 

 supply of coals to the fire. It opens and shuts its valves 

 with absolute precision as to time and manner ; it oils its 

 joints; it takes out any air accidentally entering parts 

 which should be vacuous; and when any thing goes 

 Avrong which it can not of itself rectify, it warns its at- 

 tendants by ringing a bell ; yet, with all these qualities, 

 and even when exerting a force of six hundred horses, it 

 is obedient to the hand of a child. Its aliment is coal, 

 wood, and other combustibles. It consumes none while 

 idle. It never tires, and wants no sleep. It is not sub- 

 ject to any malady when originally well made, and only 

 refuses to work when worn out with age. It is equally 

 active in all climates, and will do work of any kind ; it is 

 a Avater-pumper, a miner, a sailor, a cotton-spinner, a 

 weaver, a blacksmith, a miller, a printer, and is indeed of 

 all occupations ; and a small engine in the character of a 

 steam pony may be seen dragging after it, on an iron rail- 

 way, a hundred tons of merchandise, or a thousand j^er- 

 sons with the speed of the wind." 



Steam-engines have been much used on large farms in 

 England for thrashing, grinding the feed of animals, cut- 

 ting fodder, and for other purposes. A successful English 

 farmer has used a six-horse steam-engine to drive a pair 



