Leading Foresters. 95 
value of stands. His “Forest Mathematics” (1835) 
in which he introduces factors of form and many other 
new ideas was an original contribution to science. 
Very different in character from these four leaders 
was the aggressive, sharp-witted Friedrich Wilhelm Leo- 
pold Pfeil (1783-1859), who, without a university edu- 
cation, and in spite of his poor knowledge of mathe- 
matics and natural history, advanced himself by native 
wit and genius. After a brief period of employment in 
private service, in the province of Silesia, he accepted 
the position of professor of forestry at the Berlin Uni- 
versity in 1821 in connection with Hartig, with whom, 
however, he was at sword’s point. It was at his insti- 
gation, with the assistance of von Humboldt, that the 
school was transferred, in 1830, to Eberswalde, Pfeil be- 
coming its director. 
While Hartig was a generalizer, Pfeil was an indi- 
vidualizer, free from dogma and most suggestive; a free 
lance and a fighter. Critical in the extreme and prolific 
in his literary work, he domineered the forestry literature 
of the day by means of his Kritische Blaetter, a journal 
of much import and merit. 
The youngest of the group, Gustav Heyer (1799- 
1856), a thoroughly educated man, combined the pro- 
fessorial position in the University of Giessen (1835) 
with practical management of a forest district, but in 
1843 abandoned the latter in order to devote himself en- 
tirely to literary work. He was one of the clearest and 
most sytematic expounders, and both his Waldbau (silvi- 
culture, 1854) and his Waldertragsregelung (forest or- 
ganization, 1841) are classics. He devised one of the 
most rational methods of forest organization, and, im- 
