1S8 THE INCREMENT. 



Example. — A Scotch pine wood GO years old contains — 



Timber = 3,300 culnc feet, worth 4(/. per cubic foot. 

 Firewoods 760 ,, ,, „ Id. „ 



Hence, mean quahty — 



3,300 X 4 + 760 X 1 o. -, 

 q = ^ = 3 44 pence. 



The same wood in the year 70 has — 



Timber = 3,820 cubic feet, worth 5(1. a cubic foot. 

 Firewood =710 ,, ,, ,, Id. 



Hence- 



And 



,. 3,820 X 5 + 710 X 1 ..o^ 



(J= -J^ =4-3. pence. 



4-37 = 3-44 X l-O^^/" 



loy(100 + 7V _ , ^^^ 



And 



.) I log 4-37 — lo g 3 jl4 

 ])^ = 2*42 per cent. 



Approximate value — 



4-37 - 3-44 ,, 200 ^ qq , 



What has been said above can also be applied to the inter- 

 mediate returns. Indeed, the quality increment of that part of 

 a wood, which yields the thinnings, can be very considerable, 

 especially while the wood is still young. Here, a few years' 

 extra growth may cause a great rise in the quality per unit of 

 measurement. On the other hand, if thinnings are kept over 

 too long, they interfere with the proper development of the 

 major part of the wood; hemje, extremes iu tliis respect must 

 be avoided. 



