238 THE MEASUREMENT OF STANDING TREES 



The Klaussner principle differs from that shown in Fig. 43 only 

 in that the height is measured on the vertical scale be, the measure- 

 ment may be taken at any point from the tree by adjusting the scale 

 Ac to correspond with this distance, and the triangles may be of any 

 form, provided one side is vertical. 



Merritt Hypsometer. The Merritt hypsometer is a scale placed on 

 the reverse side of the Biltmore stick (§ 191) and is read by holding the 

 stick in a vertical position at arm's length, when standing at a given dis- 

 tance from the tree. 



Six inches on the stick will give the height of a 16.3-foot log under 

 the following conditions: 



Arm length, inches 23 24 25 26 27 



Distance from eye to tree, feet 62.5 65.2 67.9 70.6 73.3 



The similar triangles used here correspond in principle with those 

 of the Klaussner hypsometer. 



For accurate results the stick must be held vertically and not raised 

 or lowered during the reading. Only approximate accuracy can be 

 secured, but the method serves as a ready check on ocular measure- 

 ments of log lengths. 



196. Methods Based on the Similarity of Right Triangles. The 

 second general method for measuring heights is the use of the right 

 triangle. This method is based on securing a horizontal line of sight 

 from the eye to a point on the bole of the tree, and requires two 

 readings, one above, the other below this point of intersection, the sum 

 of which gives the height of the tree. This disadvantage is offset by the 

 fact that these instruments may be held in the hand, thus eliminating 

 the tripod, and making them compact and portable. 



The horizontal line of sight may be secured by using either a bubble 

 or a plumb-bob. The simplest application of this method is that of a 

 right isosceles triangle, for which purpose a clinometer is used. This 

 is an instrument with bubble mounted on a graduated arc reading in 

 per cents, or in degrees. In the latter case the graduations must be 

 reduced to per cents. 



When the arc on this clinometer is set at an angle of 45°, the line 

 of sight A b coincides with the line ABata definite distance from the 

 tree, from which a horizontal line of sight, which can then be taken by 

 setting the arc at zero, gives a distance to the tree equal to the height 

 of the tree above the intersection of this line with the bole. If used 

 on fairly level ground, the distance below this point is within reach and 

 can be measured on the tree and added to the distance to the tree to 

 get its total height. 



This instrument can also be used to measure heights from any dis- 

 tance from the bole, by taking two readings or angles, one to the upper 



