OF THE POLAR SEA. 



251 



of celestial observations made during these 

 intense frosts. The results of this and ano- 

 ther similar observation are given at the 

 bottom of the page.* 



* " The observed meridian altitude of 0 upper 

 limb was 2° 52' 5V'. Temperature of the air— 45° 5'. 

 By comparing this altitude, corrected by the mean 

 refraction and parallax, with that deduced from the 

 latitude which was observed in autumn, the increase 

 of refraction is found to be 6' 50", the whole refrac- 

 tion, therefore, for the altitude 2° 52' 51" is 2V 49". 

 Admitting that the refraction increases in the same 

 ratio as that of the atmosphere at a mean state of tem- 

 perature, the horizontal refraction will be 47' 22". 

 But the diameter of the sun, measured immediately 

 after the observation, was only 27' 7", which shows 

 an increase of refraction at the lower limb of 3' 29". 

 The horizontal refraction calculated with this differ- 

 ence, and the above-mentioned ratio, is 56' 3", at the 

 temperature - 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. January 1st, 1821. 

 Observed the meridian altitude of 0 lower limb 2° 

 35' 20". 0 apparent diameter 29° 20'. For ap- 



* 



