THE USE OF THE ABNEY HAND LEVEL. 

 By M. L. Erickson. 



For two winters I have experimented with the use of the Abney 

 level in timber reconnaissance with the view of using it as a sub- 

 stitute for the aneroid barometer. For winter use the aneroid 

 barometer has proven very unsatisfactory. Probably the main 

 reason for this is the constant great change in atmospheric pres- 

 sure distributed over small areas. The atmospheric changes 

 apparently vary and change greatly in areas as small as a square 

 mile. It was found that careful camp aneroid readings taken 

 hourly failed to provide the desired corrections of the field read- 

 ings, for even after these corrections were made it was nothing 

 uncommon to still find an error of 200 to 300 feet. Perhaps, the 

 aneroids we used were not sufficiently high class to register true 

 atmospheric pressure. At any rate, I have found it necessary 

 to abandon, for the most part, the use of the aneroid barometer 

 in winter cruising and I think, the Abney level should be substi- 

 tuted for the aneroid in summer work also. 



The use of the Abney hand level was found to work satis- 

 factorily practically in all forest conditions. The greatest ob- 

 jection to it at first was the amount of computation necessary to 

 determine elevations. It involved long office work and I did not 

 care to employ the Abney so long as its use seriously increased the 

 cost of the work. This winter, however, I have prepared a 

 table by which all office computation is eliminated, and the ele- 

 vations can be carried in the field and noted on the field sketch. 

 Mr. W. J. Paeth has devised a scheme by which the office compu- 

 tation due to the use of the Abney is very materially lessened, and 

 I think his plan is practicable and cheap enough where a draughts- 

 man is employed steadily in the office. But I was not satisfied 

 until all office computation was eliminated and also the added 

 expense of a camp draughtsman. This winter's experience has 

 demonstrated that the office computation is not necessary and the 

 use of the Abney was found to be entirely practicable. 



The table used is based on readings in per cent, but similar 

 tables can readily be prepared for Abney levels graduated in de- 



