FOREST INSTRUMENTS. 149 



measured with a steel tape, and the instrument adjusted to that 

 distance by the slide and vertical scale. The top and bottom of 

 the tfee are then sighted and the readings of the marginal scale 

 where the plumb line crosses it added to or subtracted from 

 each other, according as the eye of the observer is above or 

 below the level of the tree. This instrument may also be used 



V \ 



^ 





Figure 40. Faustman's mirror hypsometer. (ABCD.) Frame of in- 

 strument, () mirror in which scale is reflected, (a) eyepiece, (b) cross-wire 

 on which object is sighted, (gc) slide and vertical scale for distance of ob- 

 server from tree, (f) spring to hold slide in place, (/t) marginal scale which 

 gives height of tree. 



in taking levels and grades, and may be mounted on a Jacob 

 staff or tripod, but is more often used in the hand. Another 

 instrument, called "Baummesser" by the Germans, mounted on 

 a tripod, is used to take heights, and by means of a stadia 

 attachment the diameter at any point on the trunk of the tree 

 may also be measured. After some practice with one of them a 



