BOARD OF AGRICULTURE. 



were one to judge from what he sees, crowning is a favorite fea- 

 ture with our road-builders. i\.hnost everywhere the roads are 

 rendered excessively convex by scraping upon them whatever of 

 loam, sand, clay or mud can be obtained at their sides. Frequent- 

 ly they are made, by piling up this unstable material, about as 

 Eound as a log, hardly safe according to the requirement of the 

 law. 



Road Dynamics. 



Let us now consider the load that can be drawn upon roads of 

 different quality. From experiments which have been made with 

 much care by scientific men, we learn several important facts 

 about traction, or draught, upon roads. It is true that no conclu- 

 sions, mathematically exact, have been reached, yet they are suffi- 

 ciently exact for ordinary purposes. 



It is assumed, by convention, that the horse performs an average 

 day's work, on a hard, smooth, level road, when he exerts a force 

 of 150 lbs. for 8 hours and travels 20 miles, or 2| miles an hour. 

 This is equivalent to the horse power of Watts, or the elevation of 

 33,000 lbs., one foot in one minute. Careful experiments, how- 

 ever, show that this figure is too high for the ordinary horse ; that 

 120 lbs., perhaps a smaller figure even, would come nearer the 

 truth. But we will take 120 lbs., with a velocity of 2| miles an 

 hour, for 8 hours, over a hard, smooth, level road, as the unit of 

 ordinary horse-power. 



Now, in an estimate of draught, all these things must be con- 

 sidered — gravity, friction, grade and velocity. 



The gravity to be overcome, which is always the same, whether 

 the road be rough or smooth, increases with increase of grade. 

 With a grade of 1 in 100, a hundredth part of the load must be 

 lifted ; with a grade of 1 in 20, a twentieth part of the load must 

 be lifted; and one-tenth, with a grade of 1 in 10. But further: 

 While there must be, with increase of grade, a proportional in- 

 crease of drauglit, due to increase of gi'avity, yet the horse cannot 

 exert so great tractive force as when moving on a level. Not only 

 must the animal lift its own body, and simply to lift this 12,000 

 feet constitutes a fair day's work, but, because of its anatomical 

 structure, its drawing power is otherwise diminished when ascend- 

 ing a hill. On a level the horse can draw the load that is drawn 

 by five men ; up a step hill it cannot draw more than the load of 

 three men. Thus there results, in two ways, a loss of animal 



