Development of Mensuration. 75 



average diameter, to which Hennert added the volume 

 of a cone with the difference of the two diameters as 

 a base, to make the total tree volume. 



Most measurements of standing trees were, of 

 course, made on the circumference, for, in the absence 

 of calipers, the diameter could be directly measured 

 only 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 

 diameter at any height, similar to some more modern 

 ones, was constructed by Reinhold. 



Determination of the real wood contents in a cord 

 of wood and of the volume of bark by measurement 

 was taught by Oettelt, and the method of immersion 

 in water and measuring the displaced volume, by 

 Hennert (1782). 



In 1785, Krohne first called attention to the vari- 

 ation of the increment in different age classes and 

 the need of determining the accretion for each separ- 

 ately. 



In 1789, Trunk taught how to determine average 

 felling age increment, and also the method of deter- 

 mining the change of diameter classes, which is now 

 used by the United States Forest Service: "On good 

 soil a tree grows one inch in three years, on medium 

 soil in four years, on poor soil in five years." With 

 this knowledge, the attainment of a given diameter, 

 or the change from one diameter or age class to the 

 next could be calculated. 



Volume tables were at Trunk's command, and 



