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 Yierenlelee, 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 jB.rst real hypsometer mth movable sights was 

 described by Jung in 1781, and a complete instrument, 

 which could be used for measuring both height and 



