Methods of Mensuration. 69 
Until nearly the middle of the 18th century surveys 
of exact nature were almost unknown; only when the 
division into equal or proportionate felling areas became 
the basis for determining the felling budgets, did the 
necessity for such surveys present itself. 
Plane table and compass were the instruments which 
came into use in the beginning of the 18th century. But 
not until the latter half of that century were extensive 
forest surveys and maps of various character made, espe- 
cially in Prussia under Wedell, Kropff and Hennert. 
The methods of measurement of wood developed still 
later. Until Oettelt’s time no method of precise de- 
termination of volumes was known, everything being 
estimated by cords or by diameter breast-high and 
height, or by the number of boards which a tree would 
make (board feet ?). 
The diameter was sometimes used as a price maker, 
the price increasing in direct proportion to the diameter 
increase. Oettelt calculated the volume of coniferous 
trees as cones and Vierenklee, who wrote a book on 
mathematics for the use of foresters, calculated timbers 
with the top removed by the average diameter, to which 
Hennert added the volume of a cone with the difference 
of the two diameters as a base to make the tree volume 
Most measurements of standing trees were, of course, 
made on the circumference, for, in the absence of 
calipers, only the diameter could be directly measured 
on the felled tree. Doebel had already measured 
the height by means of a rectangular triangle and 
the first real hypsometer with movable sights was 
described by Jung in 1781, and a complete instrument, 
which could be used for measuring both height and 
