TRAIL SURVEYS. 63 



uphill and taking a sight on the ground at a point 100 

 feet distant, or by sighting downhill at the top of a pole 

 which is 10 feet high and 100 feet distant. 



For running different gradients, of course the height of 

 the surveyor's eye remains the same, and the length of 

 the sight is changed according to the grade. Thus, a 

 sight on a 10-foot pole, looking downhill, in a distance 

 of 50 feet, would give a 10 per cent grade; and a sight, 

 uphill, on the ground at a distance of 50 feet, would give 

 a 10 per cent grade, still assuming the height of the sur- 

 veyor's eye to be 5 feet. In the same manner, if the 

 sights, both uphill and downhill, were 200 feet, the 

 grade would then be 2J per cent. 



The use of these instruments is to some extent a mat- 

 ter of individual preference. 



In the large majority of cases the grade should be 

 located by a downhill survey. This is always the case 

 when a pass or saddle is the salient high point. When 

 the grade connects two salient points the location may 

 be run in either direction. The alignment of the trail, 

 or its meanders, may be determined by a compass sur- 

 vey after the trail is constructed. It is a matter of sec- 

 ondary importance and should be given no considera- 

 tion if it takes any time which might have been spent 

 in getting the best possible grade. The importance of 

 alignment should not be entirely overlooked, however, 

 and where two or more routes would give equally satis- 

 factory grades, then the one should be chosen which will 

 have the most favorable alignment, together with short- 

 ness of distance, and which will require the least number 

 of bridges and culverts, and in other respects afford the 

 most favorable conditions for construction. 



