HYPSOMETERS BASED ON PENDULUM OR PLUMB-BOB 241 



the string and plumb-bob. The two arms when not in use can be placed 

 within the cylinder. The instrument is more durable than the Faust- 

 niann but slightly less accurate. 



Forest Service Hypsometer. A more durable type of hypsometer 

 based upon this principle is known as the Forest Service hypsometer. 

 The distance at which this instrument reads the heights BD and DC 

 is fixed at 100 feet. The scale showing these heights is computed from 

 the tangents of the angles read at this distance and expressed in terms 

 of feet in height. This scale is placed on a circular pendulum which 



Fig. 48. — Mot hod of application of the Faustmann hypsometer. 



is released by pressing a small knob with the thumb while sighting 

 through a peep-hole along the line of sight AB ov AC. This scale is 

 enclosed in a metal frame in the form of a disk, and the instrument is 

 practically indestructible and can be operated with one hand. If read 

 at 50 feet, the readings shown must be divided by two. If at 200 feet, 

 they must be multiplied by two, and proportionately for other distances. 

 As in the case of other clinometers this hypsometer may be used to read 

 per cents of grade. 



The Winkler Hypsometer. The same principle may be used in 

 constructing a hypsometer in the form of a square or rectangular 

 board or cardboard. In this instrument the line of sight, AB, coin- 

 cides with the top edge of the board, 



A board whose top and bottom edges are parallel is laid off with a 



