Diagram A. Declination disturbances given in Curves of equal value 5° 10° 20° 30 o 40°and 50° 
llui figures repr&serut tl\ie amount of disti crtjances in degrees and the dots show the points of obserx'atLoih. 
. denote equal values of disturbance of five needle JZastwcuxt ) 
_ „ . . Westward.) of the true Meridian. 
- are linos of rto chstzubance. 
The Decluicifrm at Reader's Head, near Cossack being taken as ■ zero. 
The letters D l , D z and P 2 show the positions of disturbance of Vertical force _ see Table HI. 
