1886.] 



On Local Magnetic Disturbance in Islands. 



85 



observations has been made than in the other islands, and as the re- 

 sults are remarkable they are the first to be discussed. 



Table I shows some values of the declination observed previously to 

 the " Challenger's " visit in 1873, but reduced to that epoch by allow- 

 ing an annual change of 2' increasing. This annual change has been 

 deduced from the best available observations at four stations. 



Table I. — Declination at Bermuda, 1873. 



Station. 



Bastion C, Ireland Island 



» » • • 



j» j> 



Fort Cunningham Flagstaff 



Hen Island Magazine 



(Near) lighthouse on Gribbs' Hill . . 



In the dockyard 



Mount Langton 



Anchorage fH.M.S. "Boscawen" 

 in G-rassy ■( „ " Cornwallis" 

 Bay. L- ,r "Pembroke" 

 Green outside dockyard ...... 



Declination. 



7° 24' 

 8 00 



6 26 

 5 00 



7 54 

 3 56 



W. 



Difference 

 from normal. 



+ 0° 6' 

 + 42 

 -0 52 

 -2 18 

 + 36 

 -3 22 

 + 12 

 + 1 42 

 -0 06 

 -0 05 

 + 01 

 Normal 



Observer. 



Hill. 

 Barnett, 

 Bodie. 

 Barnett. 



Bodie. 

 Hill. 

 Lefroy. 

 Bodie. 



" Challenger. 



In Table II are recorded the magnetical results of the " Challenger " 

 observed at Bermuda in 1873. 



In Tables I and III will be found the differences between the 

 observed magnetical elements and the normal values at a station on 

 the green outside the dockyard, deduced from the results of swinging 

 in a position 15 miles south of it. 





Results of swinging at sea, 

 corrected for effects of ship's 

 iron. 



Correction for diff. 

 of geographical 

 position. 



Resulting normal 

 values at green outside 

 dockyard. 



1 

 I 



1 





+ 5' 

 + 15' 

 + 0-03 



7° 18' W. 

 65° 33' N. 

 21-25 



In the accompanying diagram No. 1 the differences of declination 

 are shown at each station, and in diagram No. 2 the differences of 

 inclination and vertical force. 



These results appear to point to the existence of a strong focus of 

 blue magnetism situated above the position indicated by the dotted 



