Methods of Mensuration. 71 
the original number of pegs that had been taken out, 
the difference gave the number of trees in each diameter 
class, and by multiplying the average cubic contents of 
a measured sample tree in each class by the number in 
the class its volume was found. 
The method, often employed at present, of ascertain- 
ing by tally the diameter classes on strips forty to 
fifty paces wide, the so-called strip method, was described 
by Zanthier in 1763. 
These measurements were usually confined to sample 
areas, the use of such being already known in 1739. The 
contents of the sample area, if a special degree of ac- 
curacy was desired, was ascertained by felling the whole 
and measuring. 
Oettelt, of mathematical fame, was the first to publish 
something about the determination of the age of trees 
by counting rings, although the practice probably ante- 
dates this account. He knew of the dependence of the 
ring width on the site and on the density of the stand. 
It seems that long before this time the French had 
made the determination of yield in a more scientific 
manner, Réaumur reporting in 1721 to the French 
Academy comparative studies of the yield of coppice and 
of volumes of wood. 
Oettelt, too, laid the foundation of forest financial 
calculations when he ascertained the value of a forest 
by determining the value of an acre of mature wood— 
the oldest age class—and multiplying it by half the 
acreage of the whole forest, suggesting the well known 
expression for the normal stock (5) soon after to be 
developed by an obscure Austrian tax collector. 
