BRANDIT'S HYPSOMETER 427 



pressure on the button is withdrawn. On fairly level ground 

 the upward angle, from a line horizontal with the observer's 

 eye to the very tip of the tree, is first ascertained, by looking 

 through the eye-piece and releasing the dial by pressing 

 the button ; when the cross wires cut the top of the tree and 

 the dial is steady, it should be fixed by taking the pressure 

 off the button. The angle can then be read ; and, having 

 measured the horizontal distance from the centre of the tree 

 to the observer, the height of the tree, from a point in a line 

 horizontal with the eye, can be ascertained by reference to 

 tables. 1 To the height thus ascertained must be added the 

 length between the ground level and a point on the tree in a 

 line horizontal with the observer's eye. This will give the 

 correct height of the tree. 



If the observer be standing on much higher ground than 

 that upon which the tree is growing, it will be necessary to 

 measure the tree in two lengths, and add the two together. 

 The first length is from a line horizontal with the observer's 

 eye to the top of the tree, and the second length is from the 

 same horizontal line to the bottom of the tree. 2 The sum of 

 these two will give the height of the tree. 



There are other hypsometers, such as Weise's, Faust- 

 mann's, Konig's, which may be preferred by some. The 

 principle of all is that of trigonometrical relations. 



The basal area at breast high is obtained by taking 

 the diameter over bark at 4% feet above the ground. The 

 basal area is the product of: 



(Diameter) 2 x . 

 4 



The diameter is taken in inches by means of callipers, or 

 of a tree compass. Callipers are preferable to the tree compass, 

 as the latter is usually heavier and is apt to give too small a 

 diameter. For very great accuracy, two diameters at right 

 angles to each other should be measured, and the mean of 



1 Tables for use with this instrument will be found in Appendix A. 

 The hypsometer may be obtained from Herr Max Woltz, Bonn, 

 Germany. 



2 The downward angle being read. 



