INSTRUMENTS USEFUL TO A WOODSMAN. 97 
instrument to be mounted upon a Jacob staff or upon a tripod. 
| The support also comprises a ball-and-socket joint, by which the 
compass is leveled with the aid of spirit tubes on two sides, a 
swivel, which permits the compass to be turned in sighting it, and 
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Fig. 6.—Measuring the height of a tree by means of two poles. 
a set screw for securing it against turning after sighting. When 
not in use the sights are folded down and the support unscrewed. 
When taken apart the entire instrument is in compact form for 
transportation, and, being made of aluminum, it is not heavy. 
The price is between $20 and $25, without staff or tripod. 
38850°—Bull. 36—10-—7 
