HIGHWOODS, COPSES, ETC. 265 



this will result in presenting an indented inclined 

 plane. And the area of this will be calculable (as 

 that of a right-angled triangle) by multiplying 

 the height of the triangle (representing the fall 

 of mature timber for each year) into the base 

 (representing the number of years forming the 

 period of rotation), and dividing the result by 

 two ; because the indentations can be eliminated 

 as above shown in summarising the arithmetical 

 progression. From this it will be very clear that 

 the length of rotation not only reduces the area 

 that can be cropped annually, but also adds very 

 considerably to the capital required in timber. 

 Suppose, for example, that there are two 

 estates having each 800 acres of similar land 

 under mixed crops of larch and pine, and that 

 one of them is worked on an eighty years* 

 rotation, with an annual fall averaging 10 

 acres, while the other is cropped with a rota- 

 tion of one hundred years, and an annual fall 

 averaging 8 acres; and suppose, also, that 

 the yield of the mature crop is in the former 

 case 7000 cubic feet per acre, while in the 

 latter it is 8500 cubic feet; then, in the 

 former case, the capital required in timber 



