142 THE WOODSMAN S HANDBOOK. 
can be taken. The number now opposite the index mark is the 
percentage of the angle formed by a line running from the ob- 
server's eye to the top of the tree and a horizontal line running 
from him to its trunk. This percentage is the ratio between the 
height of the tree above the level of the observer’s eye and the 
horizontal distance from the observer to the tree. This value is 
multiplied by the horizontal distance from the observer to the 
tree. Theresult is the height of the tree above the level of the ob- 
serverseye. The observer then sights the instrument to the base 
of the tree, operates it as before, takes the reading from the left- 
hand scale, multiplies the value thus secured by the horizontal 
distance from him to the tree, and adds this result to the result 
previously obtained, and thus secures the total height of the tree. 
These computations may be greatly simplified by taking all obser- 
vations at a distance of 100 feet or 100 yards from the tree. | 
A more elaborate form of the instrument is furnished with a 
hinged cover to shut over the glass and with two sights located at” 
the upper corners of the panel. 
COMBINED SURVEYORS’ HAND LEVEL AND 
CLINOMETER. 
This instrument (shown in fig. 12) has a telescoping surveyors’ 
hand level of ordinary construction, except that its spirit tube is 
located above instead of in its main tube, which, however, con- 
tains the usual inclined steel mirror and sighting cross wire. 
Combined with the hand level is a clinometer comprising a 
plate screwed to one side of the main tube of the hand level and 
having engraved upon it a curved right-hand scale and a curyed 
left-hand scale. These scales are struck from the same center and 
meet ata zero point, from which they are graduated outward in 
degrees to 90. A measuring arm, having a spatulate lower end 
beveled to receive vernier graduations, sweeps these scales. This 
arm is carried by a short shaft journaled in the upper edge of the 
plate and concentric with the two curved scales. The outer end 
of the shaft is furnished with a knurled hand wheel, by which the 
clinometer is operated. The inner end of the shaft carries a frame 
supporting the tubular case containing the spirit tube of the hand 
level, the center of the case being cut away to show the bubble in 

