THE PRINCIPLE OF THE CHRISTEN HYPSOMETER 243 



198. The Principle of the Christen Hypsometer. Many hypsom- 

 eters have been invented, principally by Continental foresters, using 

 one or the other of these general principles. The Christen hypsometer 

 introduces a different principle but has no special merit except the 

 simplicity of its operation. Description of this instrument, taken 

 from Graves' Mensuration is as follows : 



This instrument consists of a metal strip 16 inches long, of the shape shown in 

 Fig. 51. The instrument is made of two pieces hinged together, which are folded 



Fig. 50. — Winkler Hypsometer. 



when it is not in use. A hole is pierced in the upper end, from which it is suspended 

 between the fingers. Along the inner edge is a notched scale which gives directly the 

 readings for heights. The instrument is used as follows: A 10-foot pole is set against 

 the tree. The observer stands at a convenient station whence he can see the tip and 

 base of the tree and also the top of the 10-foot pole. The instrument is suspended 

 before the eye and moved back and forth until the edge 6 is in line of vision to the 

 top of the tree and the edge c in line of vision with the base. The point where the 

 line of vision from the eye to the top of the 10-foot pole intersects the inner edge 

 of the instrument indicates on the scale the height of the tree. 



