METHODS OF MAP MAKING 131 



elevation is found directly from the slope observation; 

 second, with similar directness surface chainage is con- 

 verted into horizontal distance. These two things are the 

 essentials wanted. To facilitate the work, the graduations 

 on the trailer of the tape correspond with those on the arc 

 of the clinometer. 



The method will be grasped from the accompanying 

 figure and the following explanation : If a party is ascend- 

 ing the slope indicated in the figure, the man ahead (who 

 serves not only as head chainman, but runs the compass, 

 takes notes, and sketches topography), as the tape comes 

 to its end, sights with his clinometer at the height of his 

 eye on the rear man (who may be the timber cruiser as 

 well as rear chainman). The reading obtained, in this 

 case 38, is the vertical rise per 66 feet horizontal on the 

 slope between the two men. That corresponds to a vertical 

 angle of 30, but the fact, not being needed, is neglected. 

 The topographer now calls out "38" to the rear man, who 

 lets the tape run out to that mark, as a matter of fact 20.42 

 feet beyond the two-chain point. When the chain to this 

 mark has been drawn straight and taut and pins are set, 

 two chains is the horizontal distance between them. This 

 the topographer may now plot on his map. The height of 

 the new point (twice 38, or 76 feet above the first one) may 

 also be used as the basis of sketching. 



