MAaNBTIC SURVEY OP GREAT BRITAIN. 



83 



Table XVIII. 



Note on the correction applied in Tables XVIII. to the Dips 

 observed with S 2. This needle being employed for the statical 

 measurement of the variations of the intensity, the poles were not 

 reversed in the dips obtained with it. The "observed dips" in 

 Table XVIII. are consequently a mean of four positions only of 

 the needle and circle ; namely, of the circle in the azimuths 0° and 

 180°, and the same repeated with the needle reversed on its sup- 

 ports; both ends of the needle being read, and ten readings taken 

 in each position. There are twelve stations at which the dip was 

 thus observed with S 2 ; at eight of these it was also observed 

 with Gambey's instrument, in which the poles of the needle were 



g2 



