CONSTRUCTION AND USE OF SLOPE SCALE 413 



horizontal distance in strides^ by simply taking the number on the slope 

 scale directly opposite the determined horizontal distance. 



For slopes greater than 1 degree, multiply the number found on the 

 slope scale by degrees of slope. For example : If the horizontal distance 

 between two points be 80 strides, then for a 1-degree slope between two 

 points the difference in elevation between them is the number directly 

 opposite 80, or approximately 7.5 feet. For a 4-degree slope it is 4 times 

 7.5, or 30 feet. This direct multiplication, instead of using trigonometric 

 functions, however, produces an error which increases with the size of the 

 angle. By trigonometric calculation the error in the elevation for a 

 4-degree slope is .027 of a foot, or 0.09 per cent, and only reaches 1 foot, 

 or 1.2 per cent, with an angle of 11 degrees. It may be seen that this is 

 within the allowable error and may be disregarded for the slopes en- 

 countered in such work, but correction could be made for it if desired. 



In fieldwork or in plotting, the slope scale enables the difference in 

 elevation between any two points to be determined rapidly by simply 

 laying the slope scale between the same two points on the map and reading 

 directly the number of feet of elevation corresponding to the horizontal 

 distance. For example, the horizontal distance between any two stations, 

 A and B, may have been determined by means of either triangulation or 

 pacing and recorded on the map. Then, by placing the slope scale on the 

 map with its zero at Station A, the corresponding elevation for a 1-degree 

 slope may be read directly on the scale opposite Station B. 



Conclusions 



The equipment mentioned above may be used efficiently for instruc- 

 tional purposes, either military or geologic, and for geologic reconnais- 

 sance in the field. Its extremely light weight, only 4% pounds, including 

 the alidade, renders it particularly adapted for reconnaissance work 

 in mountainous regions where climbing is involved and lightness of 

 equipment is an important matter. 



In military instruction it is adapted for exercises in traversing, inter- 

 section, and resection; positions may be accurately located by means of 

 the Italian resection, and it is especially useful for the various kinds of 

 plain and topographic sketching. The alidade and slope-card allow of 

 accuracy for such work that can not be attained with the equipment 

 ordinarily used and described in the text-books on military mapping. 



For instruction in geological field methods, the cheapness of the outfit 



s The same holds true for any unit of horizontal distance on the scale, whether it be 

 strides, feet, or meters, etc. 



