134 Germany. 



although many unsolved problems are still under 

 investigation. Still, late into the century it was cus- 

 tomary to measure only circumferences of trees, by 

 means of a chain or band, although an instrument for 

 measuring diameters is mentioned by Cotta, in 1804, 

 and by Hartig, in 1808. Schcener and Richter are in 

 1813 mentioned as inventors of the first "universal 

 forest measure" or caliper. The improvement of 

 calipers to their modern efficiency has been carried 

 on since 1840 by Carl and Gustav Heyer and by many 

 others until now self-recording calipers by {Reuss, 

 Wimmenauer, etc.) have become practical instruments. 

 For measuring the heights of trees, Hossfeld had 

 already a satisfactory instrument in 1800; a very large 

 number of improvements in great variety followed, 

 with Faustmann's mirror hypsometer probably in the 

 lead. As a special development for measuring dia- 

 meters at varying heights Pressler's instrument should 

 be mentioned, and a very complicated but extremely 

 accurate one constructed by Breymann. 



Various formulas for the computation of the con- 

 tents of felled trees had already been developed by 

 Oettelt and others in the eighteenth century and a 

 formula by Huber, using the average area multiplied 

 by length was definitely introduced in the Prussian 

 practice in 1817. The names of Smalian, Hossfeld, 

 Pressler and others are connected with improvements 

 in these directions. 



The idea of form factors and their use was first de- 

 veloped by Huber, who made three tree classes 

 according to the length of crowns, measured the dia- 

 meters six feet above ground, and used reduction 



