14 INSTRUCTIONS FOR MAKING FOREST SURVEYS, ETC. 



not necessary to remove the glass in order to sharpen 

 the center pivot. This may be done by unscrewing it 

 from the under side of the compass after the needle 

 has been clamped, although this must be done very 

 carefully, so that the clinometer pendulum will not 

 move out of place; otherwise it will be necessary to 

 remove the cover glass. 



In case of any serious injury to any instrument, it 

 should be returned to the property clerk at Ogden for 

 repairs. 



The instrument should not be kept near large bodies 

 of iron, nor exposed to electric motors or generators. 

 Compass needles are frequently demagnetized by being 

 carried in a valise in an electric car and being set 

 down over a powerful* motor, because the needle is 

 clamped (as it should be) while being carried. On the 

 other hand, the magnetism of a needle may be strength- 

 ened by laying the compass, with the needle undamped, 

 near a direct-current motor or generator or strong 

 magnet. A better plan is to unclamp the needle, and 

 after it has found its bearing, to clamp it and leave it 

 to the influence of the magnetic current. In this way 

 the continued quiver of the needle will not dull the 

 center pivot. 



Do not allow the needle to be deflected, while being 

 read, by an ax, jackknife, pencil tip, the metal band of 

 a hat, or other metal. 



THE POCKET COMPASS. 



The Forest Service standard pocket compass is a 

 strong and serviceable instrument for cruising or re- 

 tracing survey lines. Instructions for its proper use 

 are engraved upon the base dial, as shown in figure 2. 



