OBSERVATIONS ON HORSE-POWER. 515 



that the heat that raises a pound of water through one degree of 

 Fahrenheit has an energy of 772 foot-pounds. Whence, when 

 it is said, as at page 512, that the work of a horse in foot- 

 pounds is 1 2,400,000, it is signified that a horse in a day can 

 raise that number of pounds to the height of one foot, or half 

 that number of pounds to the height of two feet, the quarter of 

 that number of pounds to four feet. If a horse can raise, as 

 his day's work, 12,400,000 foot-pounds, and a man no more 

 than 702,000 foot-pounds, it is plain that a horse is not merely 

 eight times more powerful than a man, but more than fifteen 

 times more powerful ; but this discrepancy does not touch our 

 conclusions. 



Observations on Horse-power. To obtain a correct standard 

 of the average daily working power of a horse is of much mo- 

 ment. What is called horse-power in estimating the effect of 

 a steam-engine is above the average power of a horse for a 

 whole day of eight or ten hours. It is the ability to raise 

 33,000 Ib. per minute to the height of one foot. It was cal- 

 culated with care, at the instance of Messrs Bolton and Watt, 

 from the performance of the great dray-horses of the London 

 breweries. There can be no doubt that such horses, though by 

 no means the best fitted for continued great labour, are quite 

 equal to this exertion for a short time, but not for what can be 

 called a day's work. Such an exertion, continued for no more 

 than six hours, gives nearly 12,000,000 of pounds raised to 

 the height of one foot (11,880,000) ; and this is certainly 

 within the working capacity of a horse. In comparison with 

 this may be taken the labour of a man in driving piles, in 

 which the ram, a load of 42 Ib., is drawn up 3J feet 

 twenty times in a minute, so that if this exertion can be con- 

 tinued six hours, the number of pounds raised in that time one 

 foot is more than a million (1,058,436). This, however, is 

 said to be over-severe labour for a man ; yet it is only a tenth 



