ASCENT OP GRADES. 289 



commence moving down it on the slightest application of force 

 in that direction, — are repeated in nearly all treatises upon road 

 making, and need not be re-stated here. The useful deduction 

 from them and from practical experience, however, is that for a 

 well-made road, with a hard and compact surface, the inclina- 

 tion ought not to exceed 1 in 30, and for ordinary gravel roads 

 1 in 20. 



These inclinations are sufficiently safe, but a vertical rise is 

 equivalent to an increased length of road proportional to the an- 

 gle of inclination. From calculations made by means of a for- 

 mula deduced from experiments tested by Sir John Macneill, 

 it is shown that a goods wagon of six tons burden, drawn three 

 miles an hour upon an inclination of 1 in 30, one mile is equiv- 

 alent to 2.7 miles level road ; and for a stage-coach of three 

 tons drawn six miles the equivalent level road for one mile is 

 1.62 miles. 



The amount of force expended in conveying a given load over 

 a road from one point to another at a higher elevation, is equal 

 to the force of traction plus the force necessary to lift it up to 

 the elevation reached : thus if the load is carried two miles, and 

 the terminus is a hundred feet higher than the starting point, it 

 has to be lifted up that hundred feet, as well as hauled the two 

 miles. 



Any intermediate descents will not compensate for the rise, 

 but will add, by carrying the load to a lower level, to the ascent 

 to be made. 



The difficulty of making the ascent will be in proportion to 

 its inclination, and it will be necessary to start with a team of 

 sufficient strength to climb the hill, which would be greater than 

 would be needed on a level, or descending road. 



The road-covering upon steep inclinations is liable to be torn 

 up by the hoofs of the animals making extra exertions to ascend 

 with heavy loads, and is more subject to injury from deluging 

 rains, in proportion to the pitch of inclination. Hence hills 

 should be avoided or reduced as much as possible. 



These considerations are apt to be overlooked by persons 

 ordinarily having charge of improvement, or the construction 

 of roads, or otherwise they might be amended by material 

 reduction of grades, and generally with very little extra cost. 



37* 



