EXTERIOR DEFECTS 



115 



diagram measuring 4 by 14 inches, whose length equals that of the fire scar lying 

 within the inscribed cylinder, gives the deductions. As the scar gets shallower, 

 the length lying within this cylinder is les3 than its total length. Tables could 

 be worked up by a scaler to express the board-foot contents that could be cut out 

 of slabs of given thickness on circles (inscribed) of given diameter for a standard 

 length of log, allowing a minimum width of board equivalent to that used by the 

 log rule (§ 67) But ocular methods are almost equally efficient after practice. 



Deduction by Sectors. Side defects extending deeply into the log 

 (Fig. 21) cannot be slabbed off and are not easy to express by diagrams. 

 By enclosing them in V-shaped 

 areas representing sectors of a 

 circle, an idea may be obtained 

 of their extent. This method 

 may be used for any defect 

 occurring wholly on one side 

 of the geometric center of a 

 log and which is more accu- 

 rately enclosed by a sector 

 than a slab. 



Fig. 21. — Method of deducting from scale 

 by means of sectors enclosing defective 

 portion of log. 



The cull per cent for the portion of the log affected is roughly equal to the 

 ratio between the area of the circle and of the sector. This rule is exact for the 

 ratio J, and nearly so for smaller or larger sectors. The error in applying the rule 

 will average less than 3 per cent of the volume of the log, and if the defect is con- 

 fined to a short length, thi3 error is proportionately less for the whole log (from inves- 

 tigations of H. D. Tiemann); e.g., a sector equaling one-fourth of a circle calls 

 for 25 per cent cull. Cull tables may be made for this deduction, but it is equally 

 convenient to apply the percentage directly to the scale.' This latter method 

 adjusts the cull factor to any log rule (§ 89). 



Other Surface Defects. Stained sap is scaled as sound. When 

 unsound or decayed, the scaling diameter is taken inside the sap. 

 Surface checks caused by prolonged weathering as in the case of dead 

 timber, or by neglect or exposure of logs, must be scaled out in the same 

 manner as sap. Cat faces, as defined for cedar poles in the Lake States, 

 are defects on the sides of logs caused by some mechanical injury to 

 the bark which has caused a wound. A cat face may be accompanied 

 by rot, or be merely a dry face, not healed over and forming an indenta- 

 tion in the bole. According to its shape and depth, a cat face is deducted 

 either as a slab or a segment, of proper length. The term cat face is 

 also applied to a fire scar at the butt of a tree, usually partly healed 

 over, which may be sound, rotten or wormy. Any surface defect partly 

 healed over, on the bole, caused by either fire or mechanical injury, 

 whether at the butt or on the bole, may properly -he called a cat face. 

 Lightning scars, even when the tree is not shattered or killed, usually 



