The Abney Hand Level. 359 



of his line are sufficient to guide him in drawing his sketch 

 form lines. 



Passing Obstacles Encountered Along the Line. 



When obstacles are met with along the line, making an offset 

 necessary, the work of the compassman can often be simplified 

 and much sighting with the Abney avoided if the compassman 

 practices a little ingenuity in meeting the peculiar needs of the 

 situation with original methods and application of the Abney 

 principle. A few special cases are cited for example. 



1. Cliffs. Assuming that the strip ends on the edge of a steep 

 cliff. The compassman marks his position with a stone, a cut 

 branch, etc., and, having plotted the edge of the cliff on his strip, 

 he can make the offset without further sighting. Having made the 

 descent the compassman offsets back again to the line and marks 

 his position on the strip. From this new position on the line he can 

 sight back upon his former position on the cliff, and knowing 

 the horizontal distance between his first position on the cliff, and 

 his present location on the line, he can obtain the difference in 

 elevation between these two points. Drawing a heavy line to 

 indicate the sight, he enters upon the map sheet, between the two 

 points of sight, the difference in deration in feet and the degree 

 of per cent of slope. He then proceeds along the line as' before, 

 entering upon his map sheet only the per cent or degree of slope 

 of his line. 



2. Dense Bodies of Brush ivhere no offset can be made. As- 

 suming that a dense body of underbrush separates two open 

 spaces. The compassman may find it convenient to sight upon 

 the tip of a tree on or adjacent to the line, on the opposite side 

 of the brush. Marking the point of sight on his line, he proceeds 

 through the dense brush without further sighting until he emerges 

 from the brush, coming opposite the tree sighted upon along his 

 line, he marks the position. Having determined the horizontal 

 distance between his point of sight and the tip of the tree, he 

 calculates the difference in elevation of his point of sight and 

 the tip of the tree. Quickly pacing out from the tree he ob- 

 tains the height of the tree, and adds this height to the difference 

 in elevation. He has now obtained the difference in elevation 

 between his point of sight on the opposite side of the brush and 



