94 A MANUAL FOR NORTHERN WOODSMEN 



or, if difference in elevation is required, a pole or level rod 

 may be used to measure the amount. 



The instrument may be used to find the difference in 

 elevation between any two points without the use of a 

 level rod. To 'do this the observer begins at the lower 

 point, and, after levelling the instrument, sights in the 

 desired direction and notes the point on the ground ahead 

 intersected by the cross-wire. He then advances to that 

 point and repeats the operation, and so moves on up the 

 grade until the upper point is reached. As between every 

 two observations he has advanced to a height equal to the 

 distance from the ground to his eye, the height of the hill 

 will be the product of that distance by the number of 

 sights taken. 



The instrument may also be used as a clinometer to 

 measure slope. To do this the observer sights along the 

 slope parallel to the ground, and then uses the hand wheel 

 to turn the level tube until the bubble shows it is level. 

 The measuring arm, turning with the wheel and the level, 

 sweeps the scale and indicates the slope in degrees, or in 

 per cents, according as the instrument is graduated. 



In the same way, and with the aid of a table of tangents, 

 one may use the instrument to obtain the height of a tree 

 or a hill. This process is explained and illustrated on 

 page 166. 



For an improved form and more complicated use of 

 the instrument, see pages 130-131. 



SECTION IV 

 COMPASS AND PACING 



The staff compass, with folding sights, cross levels, and 

 a needle from 2| to 4 inches long, is familiar to most 

 woodsmen. It is a very compact and practical instrument, 

 has long been employed for retracing lines, and of late 

 years, as forest lands have come to be handled more 

 systematically, has attained a great extent and variety of 

 uses. It has also been constructed in a variety of forms, 

 combined with other instruments in some cases. The form 



