PROTECTION AGAINST WIND. 



Ill 



wood-capital than the formula indicates, while a rotation of 65 years 

 would need a somewhat larger amount than indicated. But by calcu- 

 lating as if the increment or rate of growth continued equal from year to 

 year, it will easily be seen from Fig. 27 (a) that the formula gives a correct 

 result say, for a coppice worked with a 10 years' rotation, though it would 

 apply equally to highwoods worked with a rotation of 50, 60, 100 or more 



Fig. 27. 



I DIRECTION OF MOST DANGEROUS WN05 

 COURSE Of THE ANNUAL FALLS 



(W WINDS') 

 (E TO W) 



(b) Part of a Regular Course of Annual Falls distributed 

 according to subordinate series of small partial falls re- 

 curring near same area only after intervals of 5 years. 



(a) Regular Series of Annua-l 

 Falls in close succession. 



8 9 



& SO OH TO MATURIT 



a 



/ 6 ii 16 zi ^ 7 u n ^^ j a /^ /a ^3 < 



9 14 fS 24 5 iQ i5 20 ^5 YfAffS 

 & SO OH TO MATURITY 



years. The series of growing crops over the whole woodland area for a 

 10 years' coppice rotation would be 



(1) In Autumn, before, the fall I, 2, 3, 4, 5, 6, 7, 8, 9, 10 years old. 



(2) In Spring, after the fall 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 years old. 



(3) At Midsummer, the mean of these , 1|, 2|, 3, 4J, 5|, 6, 7|, 8J, 

 9 1 years old. 



The true mean at midsummer forms a simple arithmetical progression, 

 whose sum is == J (10 x [| + 9|]) ; and 1 is the number of years in the rota- 



