ABSTRACT OF OBSERVATIONS WITH FOX CIRCLES. 



299 



the SHIP'S MAGNETIC FORCE. 



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

 liy the constant parameter R ; 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 

 ./= " 9 V = l 



- - 1 +a 



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



