148 ELEMENTARY FORESTRY. 



The Diameters of Trees and I/ogs are taken with a 

 pair of wooden calipers of convenient size for the timber of 

 the district A limb or scale bar, graduated in inches and tenths, 

 has a fixed arm standing out at right angles at one end, while 

 a second arm is movable along the bar so that the trunk of a 

 tree may be inclosed between them and the diameter read 

 directly from the scale. The fixed arm is held in place by a 



Figure 39. Calipering a tree. 



screw so that it may be removed for packing and transportation, 

 or so that a broken part may be replaced. The other arm has 

 an adjustable plate which keeps it at right angles to the scale bar 

 when pressed against the tree. Sometimes the circumference of 

 the tree is measured with a steel tape, one side of which is grad- 

 uated to give diameters of circles whose circumferences are read 

 from the other side. 



The Heights of Trees are determined by means of a most 

 convenient and useful little instrument, called Faustman's mir- 

 ror hypsometer. The distance of the observer from the tree is 



