480 Forestry Qtuirterly. 



to other formulae (Schumacher's rule) the author's own formula 

 is constructed, not quite so simply as the author promised. The 

 upshot of it is that Schumacher's rule, "the values per unit rise 

 with the diameters in arithmetic progression," is only partly true, 

 the curve being represented by a number of straight line parts; 

 which by shifting of the abscissae zero axis to a determinable 

 degree can be made straight : the prices then are in direct propor- 

 tion to the clianged diameters. The amount of shifting {s) for 

 different diameter classes {D to d) is capable of mathematical 



D—d 

 expression ; being for straight lines s=^P — 5 D when P 



and p are the prices for the two diameters ; and for curved parts, 



Ax 



To determine the price increment per cent, Pressler's well 



known diameter increment per cent formula, somewhat modified, 



200b 

 namely Pcfr=r-=— — z—, in which «= number of vears for which 

 D-^-nb 



the investigation is made, and &=average periodic ring width, 



200b 



during n years, is modified to -^fir-, — r— . This holds if the mea- 



* -^ D-\-nb-\-s 



surement is made in the middle of the log length, for measure- 

 ment at other places, the coefficient 200 must be varied; if breast 

 high, to 240 or 300 for .8 and .9 density (change of form factor!), 

 and if measured at Pressler's "increment middle" to 160 and 

 130 respectively for the two densities. 



Going into the discussion of the value increment of a tree, the 

 author reviews the various methods hitherto employed, and then 

 develops his own formula starting from the conception that this 

 increment is composed of the increment i. of the log volume 

 (^'^) times unit price (g^), 2. of volume of other wood (z/^) 

 times its unit price {q^), 3. of the participation of the log volume 

 in the total volume {x) or in the total value (^r) in hundreds of 

 the unit. The final result of the consideration of these factors 



200b z 

 yields the formula of value increment percent: pval::^ , — 



pj^p D—d D^d xq 



to which s^=r= X > ^"d - ^^ 



P—p^ 2 2 ' -^ xq.-\-{i—x)^^ 



