INSTRUMENTS USEFUL TO A WOODSMAN. 105 



The hand level is often of use to lumbermen in laying out roads 

 and trails and in locating dams. To use the instrument as a hand 

 level it must first be set by swinging the case containing the spirit 

 tube into line with the main tube. The observer then sights at an 

 object through the tube, which he brings to a level by the bubble 

 reflected in the mirror, and then notes whether or not the object 

 is above or below the cross wire. If the object is in direct line 

 with the cross wire it is on the same level with his eye; other- 

 wise the object is above or below the level of his eye, as the case 

 may be. 



1^ The lumberman may also use the hand level in finding the 

 height of a hill, or the height of any point on the slope of a hill, 

 as is necessary in making topographical maps. To find the height 

 of a hill, the observer begins at its base, and after leveling the 

 instrument, sights in the desired direction, and notes the point 

 ahead intersected by the cross wire; he then advances to that point 

 and repeats the operation, and so moves up the hill from point to 

 poin-t until the top is reached. As between each observation he 

 advances a height equal to the distance from the ground to his 

 eye, the height of the hill will be the product of that distance by 

 liie number of observations taken. 



The instrument may also be used as a clinometer to ascertain 

 the slope of a niU. To do this the observer sights the instrument 

 at an object on tne »Ior)e which is the same height above the 

 ground as his eye and located above or below where he stands, 



I ^according as he is sighting up or down the hill. He now uses the 

 handwheel to swing the tubular case until the bubble shows it is 

 level. The measuring arm, which swings with the case, is at the 

 same time swept over one or the other of the two scales, and 

 indicates upon it the slope of the hill in degrees. 



If the observer will provide himself with a table of natural tan- 

 gents, he may use the instrument for measuring the height of 

 trees. He sights the instrument at the top of a tree and turns the 



j handwheel until the bubble shows that the case is level, at which 

 time the measuring arm, which swings with the case, indicates 

 upon the right-hand scale in degrees the angle formed by a line 

 running from the observer's eye to the top of the tree and a hori- 



ll^zontal line extending from his eye to the trunk of the tree. He 

 then consults his table of natural tangents, which gives him the 



