148 Polar Explorations. 



where nature has placed the great depot of magnetic pow- 

 ers, and where every phenomenon of this kind is exhibited 

 on the grandest scale, we shall be able to appreciate the 

 value of these important results." 



Observations made by Capt. Parry, Lieut. Foster and oth- 

 ers, during one hundred and seventy two consecutive days, 

 induce them to suggest the following hypothesis : 



That there is a diurnal variation twice in every twenty- 

 four hours past a certain point, which they denominate a ze- 

 ro, or magnetic meridian; the westerly variation occurring 

 in the forenoon, and the easterly after twelve o'clock. " The 

 diurnal* change of direction appears to have been seldom 

 less than 1®, and sometimes to have amounted to 5° and 6°, 

 and even 7°;" and it is their opinion that the changes in 

 amount are due to the influence of the sun, and probably of 

 the moon, on the terrestrial magnetic sphere. The particu- 

 lar law of this influence remains unascertained. It is a ques- 

 tion whether the diminishing intensity of a magnetized nee- 

 dle in constant use, may not have caused some disturbance ; 

 but if that were the case, the variations should have dimin- 

 ished in a constant and regular ratio. They therefore im- 

 agine a small revolution of the polar point around its own 

 center, produced by the action of the sun. This theory ap- 

 pears to accord with observations in peculiar and various 

 situations in remote parts of the globe. In no instance was 

 the magnetic influence affected by the Aurora Borealis dur- 

 ing the three winters of Capt. Parry's residence within the 

 polar circle. The observations upon the needle were made 

 in a snow house, at a distance from the ships, in order to 

 avoid the effect of their attraction. 



Capt. Franklin remarks that when the Aurora was stream- 

 ing with prismatic colors, it had an obvious effect upon the 

 magnetic needle, but that when it was of a steady dense 

 light without motion, the needle remained unmoved. He 

 infers that the feebleness of the electric fluid in the higher 

 latitudes, where it was seen by Capt. Parry, is the cause of 

 this discrepancy ; that the prismatic colors and the activity 

 of the phenomenon at 68°, the site of his observations, being- 

 far greater than in the latitude of 73° at Port Bowen, are suf- 

 ficient to account for the different effects witnessed by him- 

 self and Capt. Parry, If the cause of the variation of the 

 needle can be ascertained, and the laws which regulate it 



* Edin. New Phil. Jour. March, 1827. 



