24 THE MEASUREMENT OF LOGS. CUBIC CONTENTS 



to read that much less in diameter for all logs alike. For more accurate 

 scaling the width of bark is deducted separately for each log. 



The caliper scale is the more accurate of the two methods for 

 commercial use. The volumes by this formula, in average logs, are 

 slightly below the actual contents. ^ 



Where the length of a log exceeds that which can be accurately 

 measured as one log by the above methods, the practice is to consider 

 it as composed of two or more shorter sections. By Smalian's method, 

 the intermediate points measured are taken as the ends of these sec- 

 tions. By Ruber's method, the middle point of each section is found. 

 In either case, calipers should be used. The length of section which 

 can be measured without subdivision depends primarily on the rapidity 

 of taper. Logs or sections whose total taper does not exceed 2 inches 

 may be scaled or measured as one piece regardless of length. In com- 

 mercial scaling logs less than 18 feet long are seldom subdivided. In 

 scientific studies 8 feet is usually the maximum length between measurp- 

 ments of diameter, and 4 feet is often required for the first or butt 

 sections. 



30. Girth as a Substitute for Diameter in Log Measurements. 

 The circumference of the circle, corresponding to the girth of the log, 

 may be used to determine the area of the cross-section.- In this case, 

 if G = girth, and B = Basal or end area, 



5 = ^=.0796^2 



47r 



A tape is used in which the results are read directly in inches of 

 diameter, each inch being equal to 3.1416 inches on the tape. A pin 

 in the end of the tape enables one man to encircle the log. 



The ratio between diameter and circumference, tt, holds good only 

 for the circle. The more eccentric the cross-section, the greater this 

 ratio Vjecomes, and the smaller the actual area in proportion to girth. 

 Hence, Avhatever error occurs by this method tends to give a cross- 

 sectional area greater than the actual area.^ 



^ Tests of 4398 spruce and fir logs measured in lengths up to 40 feet by this method 

 in Maine indicated that the scale required a correction factor of 1.049 or 4.9 per cent 

 over-run. The Measurement of Logs, Halbert S. Robinson, Bangor, Me., 1909. 



- Girth measurements are commonly used in India, and in commercial measure 

 ment of imported logs in England. In the United States, the girth of large logs is 

 sometimes taken, when more convenient than the measurement of diameter, but 



(7 



the result is reduced to diameter by the formula D=— = ..3183G. 



TT 



3 Mensuration of Timber and Timber Crops, P. J. Carter, Office of Supt. of 

 Gov't. Printing, Calcutta, 1893, p. 2. 



