18 THE MEASUREMENT OF LOGS. CUBIC CONTENTS 



measured. Abnormally large sections are found at forks or at the base of limbs or 

 are caused by swellings. Stumps cut low give a section averaging much too large 

 to indicate the true volume of the log, due to the rapid flare of the butt. 



Abnormally large diameters at the top end of logs should be measured by reduc- 

 ing the diameter to what the log would have if it held its regular form. Where 

 flaring butts are measured, the errors incurred may be serious. It is preferable to 

 adopt a method which does not require this butt measurement, or else to subdivide 

 the log by caliper measurements into shorter sections. Abnormal cross sections 

 caused by limb swellings, or knots, should be measured, if possible, by taking the 

 diameters at equal distances above and below the swelling. When logs are cut to 

 small diameters in the top, the log may taper rapidly in the last few feet, and the 

 disproportionally small diameter at the top will reduce the computed volume of the 

 log as a whole. This problem may be solved by measuring the tapering portion 

 separately as a short piece. In commercial scaling of logs which have abnormal 

 diameters, the scaler should apply a measurement which in his judgment will give 

 the correct contents of the log. 



In ordinary scaling, the diameter of logs is expressed in the nearest 

 inch with fractions entirely dropped or rounded off (§83). For accu- 

 rate volume measurements, each diameter is secured to the nearest 

 tenth of an inch, for which purpose the rule or cahpers used must be 

 graduated to tenths. In commercial practice, thickness of bark is never 

 included in measuring the diameter of a log except when the bark is to 

 be utilized, as for fuel or tannin,^ in which case the diameter is measured 

 outside the bark. 



When the diameter of the log is taken in the middle, the thickness 

 of bark must be ascertained and deducted. For accurate volume 

 measurements, thickness of bark on one side may be determined by 

 notching and measuring to the nearest tenth of an inch. Double this 

 thickness when deducted gives diameter inside bark. Or the bark may 

 be stripped from opposite faces in order to apply the calipers directly to 

 the wood. This latter method is laborious and is seldom used even 

 in scientific volume determination. 



26. The Form of Logs. Logs diminish in diameter from butt to 

 top, corresponding to the form and growth of trees. This difference 

 or loss in diameter at successive distances from the butt, is termed taper. 

 The taper of logs gives them their characteristic forms. On account 

 of this taper, logs are never truly cylindrical no matter how closely 

 they may approach the cylinder in form. 



The geometrical forms to which logs can be compared must there- 

 fore be circular in cross section and tapering. The forms suitable for 

 this purpose are the paraboloid, cone, and neiloid. 



' Exceptions to this practice may be found in some regions, in scaling, when the 

 log rule in use gives a large over-run which is offset by including width of one bark 

 (§83). 



