BRANDIS HYPSOMETER. 



25 



wheel, which is weighted on one side and swings between two 

 pivots, so that it always maintains the same position when at 

 rest. Oscillations can be ai-rested by a stop (see at s in figure). 

 That point of the wheel, which corresponds with the horizontal 

 line of vision, is marked as zero, and from this point the wheel 

 is graduated to 60^ up and down. A lens is fastened along- 

 side the eye-piece, to facilitate the reading of the angle on the 

 wheel. By directing the tube to any point, the angle can be 

 easily read off on the wheel, which preserves the same position 

 while the instrument is being raised or lowered. The wheel 

 is placed in a firm metal case. 



Fig. 17. — Branditi' Ilypsonieter and Clinometer. 

 (The front lid I'enioved, so as to show the wheel,) 



In using the instrument, any convenient position, where 

 the top and foot of the tree can be seen, is chosen, the angles 

 to the top and foot of the tree read off, and the distance from 

 the e^^e of the observer to the foot of the tree measured. The 

 height is then found by the formula (see Fig. 18) — 



D A X sin. (u + * 



H = 



COS. u 



This formula is obtained in the following manner : — 



Height - 11= I) CQaii. u + fun. I). 

 Since D O = D A x cii>'. I : 

 II = D A X vox. I [tan. u + tan. I) 



H 



B A X COS. I X 



n'ni. n X COS. I + sin. I x cos. 



COS. U X COS. I 



-. . sin. (ji + 



