OF THE POLAR SEA. 



257 



The aurora appeared with more or less brilliancy on twenty-eight 

 nights in this month, and we were also gratified by the resplendent 

 beauty of the moon, which for many days together performed its 

 circle round the heavens, shining with undiminished lustre, and 

 scarcely disappearing below the horizon during the twenty-four hours. 



During many nights there was a halo round the moon, although 

 the stars shone brightly, and the atmosphere appeared otherwise 

 clear. The same phenomenon was observed round the candles, 

 even in our bed-rooms ; the diameter of the halo increasing as the 

 observer receded from the light. These halos, both round the 

 moon and candles, occasionally exhibited faintly some of the pris- 

 matic colours. 



As it may be interesting to the reader to know how we passed 



— 45° 5'. So that in the parallel 68° 42', where, if there was no refraction, the sun would 

 be invisible for thirty-four days, his upper limb, with the refraction 56' 3", is, in fact, above 

 the horizon at every noon. 



The wind was from the westward a moderate breeze, and the air perfectly clear. Ja- 

 nuary 1st, 1821. Observed meridian altitude of 0 lower limb 2° 35' 20". 0 apparent 

 diameter 29° 20'. For apparent altitude 2° 35' 20", the mean refraction is 16' 5" (Mackay's 

 Tables), and the true, found as detailed above, is 20' 8" : which increasing in the same 

 ratio as that of the atmosphere, at a mean state of temperature, is 41' 19" at the horizon. 

 But the difference of refraction at the upper and lower limbs, increasing also in that ratio, 

 gives 55' 16" for the horizontal refraction. Temperature of the air — 41°. Wind north, 

 a light breeze, a large halo visible about the sun. January 15th, 1821. — Observed an 

 apparent meridian altitude 0 lower limb 4° 24' 57". 0 apparent diameter 31' 5", For 

 apparent altitude 4° 24' 57", the mean refraction is 10' 58" (Mackay's Tables), and the 

 true, found as detailed above, is 14' 39", which increasing in the same ratio as that of the 

 atmosphere at a mean state of temperature, is 43' 57" at the horizon. But the difference 

 of refraction between the upper and lower limbs, increasing also in that ratio, gives 48' 30" 

 for the horizontal refraction. 



Temperature of the air — 35°, a light air from the westward, very clear. 



The extreme coldness of the weather rendered these operations difficult and dangerous ; 

 yet I think the observations may be depended upon within 30", as will appear by their 

 approximate results in calculating the horizontal refraction ; for it must be considered that 

 an error of 30", in the refraction in altitude, would make a difference of several minutes 

 in the horizontal refraction.'" — Me. Hood's Journal. 



2 h 



