110 MECHANICS. 



as an ordinary horse can exert without being improperly- 

 fatigued with continued service : 



Velocity Duration of the Wo^'Tc accomplisJiedfor one day, in tons, drawn 

 per hour. day's work. one mile. 



Miles. Hours. On a canal. On a rail-road. (^ a turnpike. 



21 1 2 IIM2 520 115 14 



3 8 243 a 12 

 3Ma 59|io 153 82 10 



4 4^1 2 103 72 9 



5 29lio 52 57 7.2 



6 ' 2 30 48 6 



7 IM2 19 41 5.1 > 



8 11 Is 12.8 36 4.5 



9 .= %c 9 32 4 

 10 3]^ 6.6 28.8 3.6 



From the preceding table it will be seen that a liorse, at 

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

 work on a canal as on a rail-road ; but the resistance of 

 the water increases as the square of the velocity, 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 ^le amount of water should 

 be moved or displaced in a given time, but it must be 

 moved with twice the velocity, thus requiring a four-fold 

 force. 



The muscular formation of a horse is such that he will 

 exert a considerably greater force when working horizon- 



