ON STATICS. . 133 



force is something greater, but it cannot support the labour of more thati 8 

 hours a day, when drawing with a force of 200 pounds, or of 6 hours when 

 with a force of 240, Avalking two miles and a half an hour. It is generally 

 supposed, that in drawing up a steep ascent a horse is only equivalent to 3 or 

 4 men, and the employment of horses in walking wheels, where the action 

 is similar to that of ascending a hill, has for this reason been condemned. 

 For men, on the contrary, an ascent of any kind appears to afford a favourable 

 mode of exertion. But, perhaps, the weight of the carriage, and of the horse 

 itself, has not always been sufficiently considered in the comparison. The 

 strength of a mule is equal to that of three or four men. The expense of 

 keeping a horse is in general about twice or three times as great as the hire of 

 a day labourer ; so that the force of horses may be reckoned about half as ex- 

 pensive as that of men. The horse Childers is said, although, perhaps, with- 

 out sufficient authority, to have run an English mile in a single minute ; his 

 velocity must in this case have been 88 feet in a second, which would have 

 been sufficient to carry him on an inclined plane witliout friction, or in a 

 very long sling, to the perpendicular height of 1 20 feet. 



A large windmill, on which Mr. Coulomb made many experiments, was 

 capable, on an average, of working eight hours a day; its whole performance 

 was equivalent to our estimate of the daily labour of 34 men ; 25 square feet 

 of the sails doing the work of one labourer. The expense of the machinery, 

 with its repairs, would probably amount to less than half the expense of a 

 number of horses capable of exerting the same force. Where a stream of 

 water can be procured, its force is generally more convenient, because more 

 regular, than that of the wind. 



A steam engine of the best construction, with a. thirty inch cylin<ler has 

 the force of 40 horses ; and, since it acts without intermission, will perforin 

 the work of 120 horses, or of 600 men, each square inch of the piston being 

 nearly equivalent to a labourer. According to IVIr. Boulton, the consumption 

 of a bushel, or 84 pounds of coals, will raise 48000 cubic feet of water 10 feet 

 high, which is ecjuivalent to the daily labour of 8 4- nien, or perhaps more : 

 the value of tliis quantity of coals is seldom more than that of the work of a 

 single labourer for a day; but the expense of the machinery generally 

 renders a steam engine spmewhat more than half as expensive as the number 

 of horses for which it is substituted. According to other accounts, a 24 inch 



