THE; TRAVERSE BOARD 



101 



taken to the other known point, and set up by the range 

 back to the first. Then swinging the ruler about the 

 second point located on the sheet, the surveyor draws 

 rays from this to the same objects as before. The in- 

 tersection of pairs of rays directed toward the same object 

 in the field fixes that point upon the map. This is done 

 directly and graphically, no computation or reduction 

 being required. 



More complicated forms of the instrument, telescopic 

 alidades, the application, of the vertical angle, etc., need 

 not be here discussed, as they are hardly likely to be em- 

 ployed by other than specialists. It seems likely, how- 

 ever, that among a large class of foresters and woodsmen 

 this simple form of the plane table will find general use. 



The following survey of a small lake made with the 

 traverse board involves a somewhat more complicated 

 use of the instrument than that described above. This 

 particular piece of work took the time of two men for two 

 days, but on the ice it could have been done more quickly. 

 The steps in making the survey were as follows : 



1. Base line A B measured, the longest straight line 

 that could be had on the shore and in wading depth of 

 water. Flags set up at its ends and at C, D, E, F, and G, 

 prominent points on the shore visible from both ends of 

 the base line. 



2. Plane table set up at A as oriented by the needle. 

 Point a selected on the paper, line drawn from it in direc- 

 tion of B and a b measured to scale. Rays a c, a d, a e, a }, 

 a g drawn in direction of C, D, E, F, and G. 



Board at A Board at B 



3. Table set up at B, oriented by ranging b a at A and 

 checked by the needle. Rays drawn from b toward C and 



