The Biltmorc Stick. 



407 



of such an instrument over calipers and diameter tape in this 

 kind of work. 



As the name indicates, the Biltmore stick idea undoubtedly had 

 its origin at the Biltmore School of Forestry. Dr. Schenck 

 mentions it in his "Forest Mensuration" but gives no description 

 or explanation of its construction. 



Knowing of no published explanation of how the above men- 

 tioned scale was constructed and used, and believing that such an 

 explanation would be of interest to the profession, the writer 

 determined : ( i ) To derive a formula which might be used to 

 construct an accurate scale, (2) to use this formula in the con- 

 struction of such a scale, (3) to check up this scale for various 

 diameters by comparing its readings in actual field work with 

 caliper readings, and (4) to write an account of this investi- 

 gation. 



The problem resolved itself to this proposition : To derive a 

 formula for a scale which applied tangentially to a circle at a 

 fixed distance from the observer will give the diameter of the 

 circle. 



Assuming 25 inches as the fixed distance from the observer 

 and applying the geometrical principle of similar triangles having 

 proportional sides, we have 



AB 

 BC 



AB^ 

 B^ 



AB=25 inches, and B'C 

 Substituting these values 



Diameter, or D 



26 



