WEISE S HYPSOMETER. 31 



B}^ introdacing this value into the former equation, the 

 height is obtained as — 



H 



_ I X {tan, a -|- tan, h) 

 tan. m + tan. n 



All instruments which measure vertical angles are suited 

 for trigonometrical height measuring. For practical purposes 

 it is desirable that the instrument should not require a stand, 

 and that, besides the angles, the corresponding tangents 

 should be marked on it. 



c. Description of some of the more imful Instruments. 



Weise's Instrument. — It consists of (1) a tube T with an 

 objective in the shape of a cross at one end and an eye- 



Fig. 14. — Weise's Hypsometer. 



piece E at the other. (2) A scale fastened longitudinally to 

 the tube (called the height scale, H, Fig. 14) ; it is toothed on 

 one side, and has the zero point some distance from its end. 

 (3) A second scale, D, moving at the zero point of the height 

 scale and at right angles to it (called the distance scale). 

 From the upper, or zero, point of this scale depends a plumb 

 line P. 



When not used, the distance scale and plumb line are kept 

 in the tube. 



