CH. Ill] MENSURATION AND INCREMENT ii 



In each case g is measured in inches at the middle of the log, 

 and the length of the log, or the timber-height of the tree, is 

 measured in feet. 



As regards felled timber there is no difficulty about making 

 the measurement. For the girth, a quarter-girth tape, or a string 

 is used, while for the length an ordinary tape is used, or else a rod 

 with feet marked on it. If the shape of the tree or log is in any 

 way irregular, it is measured off into different sections of regular 

 form, and each section is measured separately. 



10. Commercial method of estimating standing timber. 



With standing timber, there are two procedures to be con- 

 sidered; first the ordinary commercial method of calculation, 

 and secondly . the method employed for purposes of forest 

 management, or for scientific investigations, in which the true 

 volume is required. 



By the commercial method, the girth is taken at 4 or 5 feet 

 from the ground with a quarter-girth tape, which gives at once 

 the quarter-girth to the nearest quarter of an inch. 



The next step is to make a deduction for bark, which in most 

 parts of the country is done by allowing one inch for every foot 

 of quarter-girth. Thus if a tree measures anything under 24 inches 

 of quarter-girth, but 18 inches or over, i| inches would be 

 deducted for bark. An oak of course has a thicker bark than 

 a beech, and an opportunity may offer of measuring what the 

 actual thickness of bark is in a tree of any given species and any 

 given size. The correct mathematical allowance is -39 of an inch 

 from the quarter-girth for every quarter of an inch of thickness 

 of bark. Ordinarily, however, the commercial rule of thumb of 

 \ inch for every 6 inches of quarter-girth is followed. 



The next step is to estimate the timber-height of the tree, 

 that is, the length of bole from the base of the trunk up to the 

 point at which the stem divides up into the njain branches that 

 form the lower part of the crown. This estimate is made by eye, 

 without using any means of measuring the height. It requires 

 practice and experience to do it accurately, and it is desirable 

 always to stand at about the same distance from the tree when 

 judging the height fit to yield sawing timber. There is of course 



