ABSTRACT OF OBSERVATIONS Willi FOX CIRCLES. 



299 



the Ship's Magnetic Force. 



The vertical component of the ship's magnetic force proceeding from sub-permanent magnetism is denoted 

 by the constant parameter E ; that part of it proceeding from transient induction in soft iron by -/. 



The vertical force is further affected by horizontal induction in horizontal soft iron, giving it a different value 

 according as the ship's head is north or south. This induced force is represented by the constant c. 



In the notation of the " Admiralty Manual " for deviations of the Compass — 



7 1 + k q * ' i 



d = - — r = =-2— A = 1 + a. 



\+a \+a 



The constants R and d, are expressed in terms of the horizontal force at Kew Observatory = 1 0. 



