The Use of the Abney Hand Level. 373 



man takes the course with a compass and the grade readings with 

 an Abney and carries his horizontal distance by pacing. 



There are numerous practices in the field that the topographer 

 soon learns to employ. 



1. Sight a definite object on ground. Determine elevation 

 at that object and then add 5 feet for distance ground to eye. 



2. Sight at peculiar markings on trunk of tree (black knots, 

 scars, wood-pecker holes, etc. ) . Add or subtract difference in feet 

 above or below approximate height of eye. 



3. Sight at peculiar definite limbs in tree. Make approximate 

 allowance for distance above eye. 



4. Sight at top of a tree or snag. Determine height of tree by 

 any of the simple methods and add this to elevation determined 

 for the top of the tree. 



A great help in plotting the contours between strip lines when 

 the course follows steep side hills is to note with the Abney the 

 slope up or down by plus or minus; the direction of slope being 

 indicated by arrows. 



The exact location and elevation of points of ridges or other 

 topographic relief not directly on line with the compass course can 

 be determined. The location is determined by bearings from two 

 stations taken with the compass, and the vertical angle is taken 

 from one of these stations with the Abney level. Knowing the 

 distance and the vertical angle, the elevation of the object can be 

 easily computed. 



The Abney is a great aid in checking one's own work in the field. 

 Often observation from stations along the strip line to tops of 

 peaks, ridges, cabins, ponds or other objects already located will 

 give a check on the elevation previously determined. 



Incidentally the tallyman need depend on no other instrument 

 for determining the number of logs or height of trees. 



On very steep hillsides, through dense brush, or across difficult 

 obstructions it is often unsatisfactory to pace the distance. The 

 Abney level can be used to determine the horizontal distance as 

 well as the vertical difference in elevation. 



Example : The cr^w arrive at the brink of a very deep canyon 

 with precipitous walls. The compassman determines an object 

 on the opposite bank for his course, then with the Abney level 



