194 BOTANICAL GAZETTE [September 



seen to decrease as the rate of wind movement is increased. Now- 

 let a line bisecting the right angle at o cut oy at c. The ordinate 

 from ojj passing through c will give a value of w which may very 

 conveniently be used as the unit. Now since i*—i, the value of y 



at this point becomes y = — — ; hence c = -— I. By substitute 



^ J i+c y 



ing this value of c into the formula with other experimental values 

 of y and w> the value of n can be obtained readily. A more general 



/.C=yf eu^y/"- £** -mJnujS: 



Fig. 3 



method of finding the value of n is by the elimination of c, as follows : 

 Going back to the original formula and solving for cw n , we find that : 



/ — /i t—tt /w\ n P 



cw n = — i=p; likewise cw* = — i = p 1 : dividing — = — ; 



whence n = . 



w 



log — 



Knowing the value of n, we can readily find c by the formula 



P t 



c = 7~\^. The first method for finding the value of c and then of 



n is quicker and more accurate when as many as four or five experi- 

 mental points on the curve oy are known, thus enabling one to 



