108 Rev. Mr Scoresby an the Uniform Permeability of 



Now, the position represented in Fig. 5. is that of No. 1, m 

 the first line of this table, in which the magnet was placed at the 

 distance of one focal length from the compass — not from the 

 centre, but, in this instance, measured from the focal poles of 

 the needle w, s. 



Therefore the distances F s and F n are each = 1 ; and F'^ 

 and F^n the distances of the remote or counteracting pole are 

 each = 2. But owing to the considerable length of the com- 

 pass needle, and the great deviation which occurred on this occa- 

 sion (namely 59° 23'), the actual distances of the two poles of the 

 needle from the nearer focus F were ^ and ^, and from the re- 

 mote focus were 1^ and 2^. Let us now see what relation of 

 forces these distances afford in comparison with those belonging 

 to the distance 1 ^d 2. 



First, As to influence of the magnet on the compass, whilst 

 the needle is in the meridional position s v. 

 The distances F.? and F ;i being each = 1, their combined 

 influence will be inversely as 1* -|- 1* or |-, which represents the 



