APPLICATION OF LABOR. 169 



From the preceding table it will be seen that a horse, 

 at a moderate walk, will do more than four times as 

 much work on a canal as on a rail-road ; but the re- 

 sistance of the water increases as the square of the ve- 

 locity, and therefore when the speed reaches five miles 

 an hour, the rail-road has the advantage of the canal. 

 On the rail-road and turnpike the resistance is about 

 the same, whether the speed be great or little, the 

 chief loss with fast driving resulting from the increased 

 difficulty with which the horse carries forward his own 

 body, which weighs from 800 to 1200 pounds. The 

 •table also shows that when it becomes necessary to 

 drive rapidly with a load, it should be continued but 

 for a very short space of time ; for a horse becomes as 

 much fatigued in an hour, when drawing hard at ten 

 miles an hour, as in twelve hours at two and a half 

 miles an hour ; because, when a boat is driven through 

 the water, to double its velocity not only requires that 

 twice the amount of water should be moved or dis- 

 placed in a given time, but it must be moved with 

 twice the velocity, thus requirmg a four-fold force. 



The muscular formation of a horse is such that he 

 H 



