1864.] made at Port Kennedy hj Sir F. L. M'Clintock, ^c. 



85 



Sea, 1200 miles distant from Port Kennedy (Captain M'Clintock's station), 

 in the winters of 1852-53, and 1853-54, published in the Phil. Trans, 

 for 1857, Art. xxiv. 



The first point established conclusively by this comparison is, that, after 

 due allowance has been made for the difference in the antagonistic force of 

 the horizontal portion of the earth's magnetism by which any disturbing 

 action on the declination-magnet is opposed at the two stations, the 

 intensity of the disturbing force is considerably less at Port Kennedy than 

 at Point Barrow — that is to say, less at the station which is nearest to the 

 points of 90° of dip, and of the maximum of the total terrestrial magnetic 

 force, than at the station which is more distant from those points. The 

 indication thus derived from the magnetic record at the two stations 

 accords with the fact of the far greater frequency of the aurora at Point 

 Barrow, where in the two winters its appearance is recorded on six days 

 out of every seven, whilst the proportion at Port Kennedy is not more than 

 one day in four. 



For the purpose of examining the periodical laws of the disturbances at 

 Port Kennedy, those which exhibited the largest differences from their 

 respective normals of the same month and hour, amounting to between 

 one-fourth and one-fifth of the whole body of the hourly observations, were 

 separated from the others, and were subjected to analysis in the customary 

 manner. It is thus shown that both at Port Kennedy and at Point 

 Barrow the disturbances so treated form themselves into distinct categories 

 of easterly and westerly deflection, — the curve representing the easterly 

 deflections having the same general form and single maximum as that of 

 the easterly deflections at Kew, exhibited in PI. XIII. fig. 1 of the Phil. 

 Trans, for 1863, Art. XII. ; and the westerly curve having the same general 

 form and double maximum as is seen in fig. 2 of the same Plate, represent- 

 ing the westerly deflections at Kew. 



A remarkable correspondence is pointed out in regard to the hours at 

 which the maxima of easterly and westerly deflection take place at Port 

 Kennedy and Point Barrow. The maximum of easterly deflection occurs 

 at the same hour of absolute time at the two stations ; and the maximum 

 of westerly deflection at the same hour of local time at the two stations. 



The author concludes by taking a general review of the phenomena of 

 the solar-diurnal variation, particularly in the vicinity of the dip of 90°, 

 where the geographical and magnetical directions of the magnetic needle 

 are often strongly contrasted. At Port Kennedy the normal direction of 

 the magnet is 35° to the east of south, and at Point Barrow 41° to the 

 west of north : the contrast at the two stations in this respect is therefore 

 nearly as great as can exist in any part of the globe, wanting only 6° of 

 180°, or of being diametrically opposite. The solar-diurnal variation at 

 these stations furnishes an apt illustration of the author's exposition. 



He further takes the occasion of the phenomena of the disturbance 

 diurnal variation at Port Kennedy, and at Nertschingk in Siberia, to show 



H 2 



