412 A. M. BATEMAN MILITARY AXD GEOLOGIC MAPPING 



CONSTEUCTION AXD USE OF SlOPE ScALE. 



AAlien the slope angle and the horizontal distance in strides^ between 

 any two points are known, the difference in elevation may be read directly 

 by the construction of either a chart or slope scale. The chart may be 30 

 made that one axis represents distance in strides, another degrees of 

 slope, and a third the corresponding difference in elevation, measured in 

 feet. The slope scale, however, was found more practical and convenient, 

 it is so constructed that differences of elevation in feet for one degree of 

 slope are read directly opposite the figure on the distance scale represent- 

 ing the horizontal distance between the two points (see figure 5, B). It 

 is constructed as follows : 



Problem: Constrnct a slope scale to be nsed with a working scale of 

 1/1000.* 



This means that 1 inch on the scale equals 1,000 inches on the ground. 



I20 ^40 , ISO (so JoJ" 



STRIPE S Tggg 



Slope Scale m feet for l«S|ope - X by decrees of slope. 



Figure 5. — Slope Scale (B) on same Ruler as Stride Scale (A) 



The slope scale is so placed as to give difference in elevation in feet, opposite the dis 

 tance in strides between two points, for any degree of slope. 



Xow, 1 degree of slope equals 1 foot rise (or depression) in 57.3 feet; 

 equals 10 feet rise in 573 feet, or 6,876 inches, on the ground. 



Thus, for 1 degree of slope, 10 feet rise (or depression) would be 

 represented on the scale by 6876/1000, which equals 6.876 inches. By 

 the method of proportion shown in figure 4, divide on paper a line 

 6.876 inches long into 10 equal parts, each one of which will represent 1 

 foot rise (or depression) on a scale of 1/1000. This may be called the 

 slope scale. These divisions may then be transferred to the triangular 

 wooden rule, so that the zero of the slope scale is set directly opposite the 

 zero of strides on the working scale (see figure 5, B). The elevation 

 divisions may be extended to the left of the zero, as shown in figure 5, B, 

 and further subdivided to read fractions of feet. Similar elevation scales 

 may be made corresponding to any desired horizontal scale or any desired 

 unit of horizontal measurement. The scale, constructed as described above, 

 will then give the number of feet elevation for a 1-degree slope for any 



3 Any other desired unit of measurement can be employed. 



* The problem is the same, regardless of what wwking scale may be used. 



