196 FELLING AND 



the tree is very high, or the distance large, the unit may be 

 taken as two feet or a yard. Thus, if the observer is standing 

 90 feet away this may be taken as 30 yards, and the scale is 

 set at 30. The height is then obtained in yards, but as the 

 scale is marked to show half units, the result is correct to 

 within 1 8 inches. 



The instrument is simple and easy to use. 



The height having been obtained, the place where the half 

 height would be on the tree is noted. An assistant takes the 

 quarter-girth with a tape as high as he can reach, and the 

 woodman estimates the fall-off in quarter-girth from this 

 place up to half height. This is difficult to do accurately, 

 especially on irregular trees. If the woodman has the oppor- 

 tunity of measuring this fall-off on large numbers of felled 

 trees he will, however, soon be able to estimate correctly to 

 within half an inch of quarter-girth. As a general rule, on 

 normally shaped trees, the fall-off is about i inch in quarter- 

 girth for every 10 feet in height for conifers, and about 

 i^ inches in 10 feet with broad-leaved trees. Taking these 

 figures as a basis the woodman must add or deduct from them 

 according to the shape of the tree. 



Having thus measured the length and estimated the quarter- 

 girth at half height, the cubic contents are worked out as for 

 felled trees, using tables, and making the usual bark allow- 

 ance if the volume under bark is required. 



When large numbers of trees are to be measured singly it 

 would be tedious to take the height of each tree with an 

 instrument ; the work can be hastened without losing much 

 accuracy by using a pole, say 20 feet long, with feet marked 

 on it. This should be propped against the tree, and the 

 woodman can then estimate the length of timber above the 

 top of the pole. Such a pole will be quite sufficient for short 

 trees, but with tall ones the estimate should be checked 

 periodically with the height measurer. After a little practice 

 the length will be obtained with a very fair degree of accuracy. 



