COUNTRY ROADS. 233 



draug-lit power, fi'om increasing the g-rade of the road. It is a vast 

 loss, when we consider that nearly all our roads are very hilly. 



When the road has a good surface, the load which the horse 

 can draw will decrease about as follows with increase of grade : 

 If the grade is 1 foot in 100, or 52 feet to the mile, the horse can 

 draw nine-tenths of what would constitute its load on a level ; if 

 the grade is 1 in 30, it can draw two-thirds of its load on a level ; 

 if 1 in 24, it can draw only one-half; if 1 in 10, then it can draw 

 oiilj^ one-fourth of its load on a level. 



It is true that the horse, for very brief intervals, can draw five 

 oa* six times its constant load on a level — can exert a tractive force 

 of 600 or 800 lbs. Except for very short distances, however, it is 

 not well to count upon more than double exertion, which is de- 

 manded when the road has a longitudinal inclination of 1 in 30 or 

 35. Hence the grade of all hills, with any considerable length of 

 ascent, should be reduced to this figure, either by going around 

 the hills, by cutting them down, or making zigzag roads over 

 them. 



The amount of force needful to overcome friction depends 

 chiefly on the surface of the road. Were the roads in Maine level, 

 with their present surface, the force required for draught would 

 probably average about one-tenth of the load. The horse exerting 

 a tractive power of 120 lbs., would draw a load of 1200 lbs., 20 

 miles, in 8 hours. But were the surface such as it ought to be, it 

 would require a tractive power of one thirty-fifth of the load, and 

 the horse would draw 120 x 35=4200 lbs. On an average level 

 gravel road it may be said that the horse can draw, in round num- 

 bers, a load fifteen times its tractive power, or 1800 lbs.; and 

 three times more than this, or 5400 lbs., on a good broken stone road; 

 and eighteen times more, or 3200 lbs., on a. good railway track. 

 Such is the important relation of surface to the load which may be 

 drawn by a horse for several consecutive hours. 



From these conclusions of practical, scientific engineers, the re- 

 sult of numerous and careful experiments in road dynamics, it will 

 be seen that the utility of roads is increased or diminished more 

 than one would at first suppose, by slight variations, whether in 

 grade or smoothness of surface. 



But, again, the tractive power of the horse decreases rapidly 

 with increase of speed, and decreases most rapidly on a rough 

 road, or ascending grade. At the height of its speed the animal 

 can only move itself. As a rule, the draught power of the horse, 



