142 



Forestry Quarterly. 



one side of the slot in which the blade is seated and a nick in 

 the blade facilitate opening. 



rr 



a) 



Co) 



A longitudinal section showing Christen arm (a) folded and (b) ex- 

 tended; (c) is the brass seat. 

 The distance between the two arms when erected is exactly 15 inches. 



At one side of the stick and along the lines' connecting the arms 

 is marked the Christen scale, based upon the use of a lo-foot pole 

 and a distance between the arms of exactly 15 inches. It is de- 

 rived according to the formula: 



height of tree distance between arms 

 height of pole scale distance 



height of pole X distance between arms 



or scale == , ■ , ^ — j— ■ 



height of tree 



The Christen, so constructed, is very accurate up to a height of 

 about 50 feet, and is thus suited to the second growth found 

 in this vicinity. If larger trees are to be measured the same de- 

 gree of accuracy can easily be obtained to a much greater height 

 by making slight adaptations. For instance, using a 15-foot or 

 a 20- foot pole the reading can be made accurately to 75 or 100 

 feet respectively by multiplying the original scale reading i^ or 2. 

 The capacity for accurate measurement could be raised to 100 

 feet by the use of a 30-inch distance between arms and a lo-foot 

 pole, to 150 feet with a 15-foot pole, or to 200 feet with a 20-foot 

 pole. Since the 15-inch distance between arms is much more 

 convenient to handle in small growth, it might be advisable to put 

 in both 15 and 30 inch Christen (using the same upper arm and 

 putting the scales one on each side of the arms) where the height 

 of trees to be measured varies greatly. If measurements are to 



