10 



correctly the volume both of the cone and of the paraboloid, and is 

 only 1*8 per cent, less than that of a cone with a concave surface. 



The rtf^-height may be estimated with the eye, or obtained 

 with the help of a special measurer .(the richt-tube). This instru- 

 ment consists of cardboard tubes telescoping one into the other. 

 At the objective end of the outer tube are fixed two wire points at 

 the extremities of one and the same diameter. The end of the 

 innermost tube is closed, except for a small hole to which the eye 

 is applied. To use the instrument, direct it on the trunk at the 

 point where the diameter has been measured, and pull out the 

 tubes until the wire points just embrace it. Then drawing- out the 

 tubes to twice this length, direct the instrument again on the tret j , 

 working it up along the trunk until the wire points just embrace it, 

 and note the point where this occurs. The diameter at that point 

 is, on the principle of similar triangles, half the original measured 

 diameter, and the height of the point is the rze/itf-height sought. 



5. Estimation by means of several diameters. 

 The measurement of diameters above the reach of a man of 

 average stature requires the use of special instruments, and hence 

 this method is seldom employed. 



6. General. 



As the fourth and fifth methods can give only the contents of 

 the stem, the contents of the branches and stump and roots must 

 be obtained by means of special tables compiled for the purpose. 



Chapter iy. ' , 

 On the measurement or Valuation Survey of Standing Crops. 



1. The Various Methods of Valuation Survey in General. 

 The most correct method of obtaining the cubical contents of 

 an entire crop would be to cube each component tree separately, 

 and then sum up the results. But such extremely detailed pro- 

 cedure is entirely impracticabie, except in the case of crops of very 

 limited extent. In practice, therefore, it is necessary to devise 

 some much more expeditious methods that will yield results accu- 

 rate enough for the purposes of the forester. 



