54 MEASUREMENT OF WHOLE WOODS. 



measured in one lot. This is a great convenience and saves 

 much time. The vohmie of all sample trees multiplied by 

 the constant c gives the volume of the wood. In this way, a 

 modification of the general method has been elaborated, which 

 is known by the name of Draudt's method. 



Draudt selects in each class the same percentage of sample 

 trees, thus ensuring, that — 



-^ ^ '^2 ^ ^ ^ _ _ 

 Si S2 S3 



Let 



T' = ri X »i + r2 X »2 + ''3 X »3 + • • • 



If J) per cent, of the trees in each class are taken as sample 

 trees, the proportion of these to the total number of trees is 



= J^ = -Op. By multiplying each term in the above 



equation by this coefficient, the following equation is 

 obtained : — 



T" X -Oj) = ri X )/i X -Op + V2 X 7/2 X -Op + /"a X U3 X 'Op -\- . . . 



Here, vi x //i x '0^) represents the volume of the sample 

 trees in the first class, r^, X n^ x '^p that of second class, kc. 

 If the volume of all the sample trees, ?i x ;;i X "O;^ + v^, x »2 

 X -Oj) + . . . = r, then 



and 



•0^; p • 



It happens generally, that the number of sample trees in 

 each class contains a fraction of one. Such fractions are 

 eliminated by considering '51 as a full sample tree and by 



