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 O, 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 cj drawn in direction of G, 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 
