588 JOURNAL OF FORESTRY 



height curve. (2) The bark thickness curve. (3) The form point 

 curve. 



One can also simply take an average form point, from readings on 

 trees of average size or even average up all form points and supply 

 the average to all sizes. This procedure is really quite accurate in 

 total results. 

 Application of the Tables 



Once these curves, etc., are ready we start to use Jonson's tables. 

 Looking up in the tables, one finds the form classes corresponding to 

 any form points. It is customary to show a form class curve with 

 the form point curve on the same ordinate and abscissa. The form 

 class is more horizontal than the form point curve. Taking from the 

 curves the d.b.h. ivithout hark, the heights and the form classes, the 

 volume is then obtained from the tables. 



The form class is expressed in decimals and usually lies between 

 0.55 and 0.75. One generally refers to the unit as being 0.01. This 

 unit only causes a variation of approximately 1.5 per cent in volume; 

 it is therefore, not necessary, for ordinary purposes, to make minute 

 interpolations for form class Init rather try to take it in the nearest 

 round figures. One can either look up the volume of the average 

 tree of each diameter class, or, only looking up for diameters in even 

 figures, draw up a volume curve. I prefer to put all the curves one 

 above the other having the same diameter scale as abscissa right 

 through, so that by following one vertical line, one gets the dififerent 

 factors from each curve in turn. 



Summarizing, the process consists in the following operations : 



1. — Tallying trees in diameter size classes. 



3. — Making observations on sample trees for height, bark thickness, 

 form point, etc. 



•'5. — Finding the averages of the different factors by means of curves 

 or otherwise. 



4. — Looking up volume in Jonson's tables using height, diameter, 

 and form class as argument; or, if for example a log specification is 

 required, getting the diameters at any point on the stems from the 

 taper tables. 

 The Use of Form Quotient Taper Tables 



One of the most common objects in using such tables is for making 

 log estimates. As a concrete example, supposing that in a certain 



