MEASUREMENT OF TIMBER 



195 



The instrument consists of a tube, T, with cross wires at O, 

 and an eye-piece, E. A toothed scale, //, is fixed to the 

 tube. D is a movable scale with a plumb-line, P, attached to 

 it. To take the height, stand at any point where the top and 

 bottom of the tree can be seen. Then measure the horizontal 

 distance to the tree. Fix the scale D in such a way that it 

 indicates, at the level of the scale //, the same number of 

 units as there are in the distance between the observer and 

 the tree. Thus, if the distance is 40 feet, set the scale at 40. 

 Look at the top of the tree through the tube, allowing the 



Fig. 14. Weise's Hypsometer. 



plumb-line to swing clear ; on getting the cross wires to 

 coincide with the top of the tree, turn the tube gently to the 

 right so that the plumb-line is caught in the teeth. Read off 

 the number at this point on the scale H. This gives the 

 height above the level of the observer's eye. Repeat the 

 operation looking at the bottom of the tree. If the plumb- 

 line is now caught on the O side of the scale D, add the result 

 to the previous one ; if it is caught on the E side of the scale, 

 subtract the second reading from the first. The total given 

 is the height of the tree in feet, if the unit is one foot. Where 



N 3 



