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 
