38 ANGULAR SURVEYING 



The right-hand page is used for remarks and sketches. 

 When no objects are to be located along the line, as in the case 

 from A to B, no sketch is necessary. Between B and C, a 

 sketch is drawn showing the location of a road and mill with 

 respect to the line BC. The line being run is usually rep- 

 resented by the center line on the right-hand page, unless 

 objects are to be located at great distances on one side of the 

 former line, in which case it is represented by a vertical line 

 drawn near the right or the left edge of the page, as may be 

 necessary. This is illustrated by the lines PQ and KL, which 

 represent parts of BC and DE, respectively. A number writ- 

 ten in the column of distances between two letters denoting 

 corners, indicates the distance at which the point horizontally 

 opposite it in the sketch is from the immediately preceding 

 station or corner. Thus, the number 100, horizontally oppo- 

 site P, indicates that the distance from B to P is 100 ft. 



Declination of the Needle. The angle that the magnetic 

 meridian or the direction of the needle is making with the true 

 meridian is called the declination of the needle. When this 

 declination is known, the true bearing of a line, that is, the 

 angle that it makes with the true meridian, can be determined 

 from its magnetic bearing by adding or subtracting the declina- 

 tion, as the case may require. 



The declination of the needle has different values in dif- 

 ferent localities, and also varies from year to year in a given 

 locality. The approximate declination of the needle in a given 

 locality at a given time can be determined from charts pub- 

 lished by the United States Coast and Geodetic Survey. They 

 show lines passing through all points where the declination of 

 the needle is the same (isogonic lines) and also Knes passing 

 through all points where the declination is zero (agonic lines). 

 These charts give also the yearly variation of the isogonic 

 lines, and may be used for obtaining approximate values of 

 declination for dates other than those for which the chart is 

 prepared. 



