SURVEYING PRACTICE 21 



to range for themselves, and lose no time waiting for the 

 set-up of the instrument. The chainmen keep behind the 

 instrument where they are out of the way. Each man 

 learns his exact duties, and all hands, particularly the corn- 

 passman and rodman, learn to work together. 



Running by Backsight. The details of compass survey- 

 ing vary considerably in accordance with the accuracy re- 

 quired, cost allowed, and the make-up of the party doing 

 the work. If local attraction is suspected or, on short 

 lines, if great accuracy is required, obstructions are cleared 

 completely out of the line, and w r hen an assumed or trial 

 course has been started, it is prolonged by backsight en- 

 tirely, reference to the needle not necessarily being made. 

 In order to do this, either a rear rodman is employed or a 

 stake is set in line at each station occupied by the compass. 



Picketing. The compass after the start, indeed, may not 

 be used at all, but straight stakes, preferably four to five 

 feet high and sharpened at both ends, may be ranged in 

 one after another along the line. This method of running 

 a line is frequently resorted to, and is called picketing. 



To clear out in most woods a line open enough for con- 

 tinuous backsighting or picketing is an expensive process, 

 and, further, this method for long distances and uneven 

 ground is not to be relied on. If, in those circumstances, 

 close accuracy of alignment must still be had, resort must 

 be made to another class of instrument, a transit or solar, 

 which may carry the work out of the hands of the woods 

 surveyor. 



Running by the Needle. Usually the compass will do 

 the work reasonably well and satisfactorily to all interested 

 parties, in which case the needle will be used at nearly 

 every setting. In all compass running it is well to carry a 

 light rod ahead, though that is sometimes dispensed with, 

 the compassman going up to a stake or even an axe set up 

 by the head axeman in line. When trees of some size are 

 run into, they are not commonly cut down, but the com- 

 passman notes, or has marked, the spot at which his line 

 of sight hits them, and, going forward, sets up beyond 

 them in the same range as nearly as he can. For back- 

 sighting it is not a great trouble to set stakes, but, in a 



