18 



TEE 1RR1 GA T10N A GE. 



at A, B, and C. The board B D is fastened to the triangle at right 

 angles to A C. An ordinary carpenter's square used in the construc- 



FIG. 1. Leveling device triangle with plumb bob. 



tion of the apparatus will insure sufficient accuracy in the position of 

 B D. Near B, on the board B D, a plumb line is made fast. The 

 plumb bob, like a mason's plumb bob, hangs in a hole, so that when B 

 D is vertical the string hangs very near the surface- of the board B D. 

 When B D is exactly vertical A C is exactly horizontal, if the angles 

 at D are true right angles. 



The dimensions of the triangles may be about a follows: A C, 12 

 feet long; A B, about 7 feet 3 inches; C 8, about 10 feet; and B D, 

 about 6 feet long. Other dimensions will do as well, the essential 

 features being the straight board A C and the board B D at right 

 angles to it and near enough to one end of A C for the man carrying 

 that end of the triangle to see accurately the position of the plumb 

 line. The board B D should not be less than 4 feet long, or the 

 plumb line will be too short to give satisfactory results. It will fre- 

 quently be found convenient to have a scale of feet marked off on A C. 



In marking on the board B D the line in which the plumb line will 

 hang when A C is exactly horizontal considerable care is required. 

 Two pegs are driven into the ground ar far apart as A and C for these 

 points to rest on. The highest one is driven into the ground until the 

 plumb line follows about the center line of the board B D. Having 

 marked this position of the plumb line, the Lriange is reversed so that 

 the end B rests OQ the peg where before we had the end C, and vice 

 versa. Should the plumb line make an angle with the first line 

 marked on the board, then the correct position will be exactly in the 

 middle between these two lines. This point should be permanently 

 marked on the board B D: in using the triangle when the plumb line 

 passes through this point the base of the triangle will be level. 



DETERMINATION OF LINE OF A DITCH. 



To use this instrument for locating the line of the ditch, calculate 



