686 ATMOSPHERIC REFRACTION AT LOW TEMPERATURES. 



Aug. 5th. — Appearances of the raising of ice in the horizon by- 

 refraction until it resembles a perpendicular wall, were generally 

 taken to be an indication of open water, but were not thought 

 by Parry an infallible one. 



4. Scoresby's Observations of Fog Bows. 



Scoresby in his Greenland Voyage (pp. 96, 144, 164) also de- 

 scribes remarkable effects of refraction by layers of air of different 

 densities ; and (p. 275) remarkable coronse or fog-bows, with a 

 number of prismatic circles, seen from the mast-head 105 feet 

 above the sea-level in a direction opposite to the sun. 



Round the centre was — 



1. A bow from 3° to 4° in diameter. 



2. A bow 9^^*^ in diameter. 



3. A bow 13° in diameter. 



These at times gave the colours of the spectrum. 



4. A circle about 5° broad, and mean radius 38° 50'. 



The upper edge of this circle was about 6° above the horizon. 

 Another outer circle was seen on another occasion. 



The sun's altitude was 35° 42'. Many shining spikes or needles, 

 supposed to be crystals of snow, were seen floating in the breeze, 

 but they were so small that they could not be caught and 

 examined under a microscope. 



The sun shone above the fog with great splendour, and the 

 shadows of the masts, sails, &c. were clearly thrown on the water. 



p. 351. Passed through brown coloured patches of sea-water, 

 the colour being due to animalcules covering the sea in streaks, 

 as shown by examining the water under a microscope. They 

 must be exposed to an average temperature 15° below the freezing 

 point in a sea perpetually covered with ice. 



Water of a similar appearance is also noticed by Parry on his 

 entrance into Davis Strait. See Journal of Voyage for Discovery 

 of N.W. Passage. 



Sometimes these streaks are of a yellowish green colour. 



5. Observations on Refraction. Paraselene. (Belcher.) 



On November 30, 1852, Admiral Belcher saw a beautifully 

 defined paraselena (see illustration in Vol. I. p. 169) about N.N.E. 

 true. The interior circle had a radius of 22° 30', the exterior 44°, 

 the moon's altitude at the time 30°. 



There were two concentric halos, incomplete near the horizon, 

 accompanied by a strong vertical and a horizontal beam passing 

 through the moon. It was also accompanied by arcs of other 

 concentric circles, having their common centre at a point within 

 the zenith. The greater of these intersected the moon and outer 

 halos, forming at their contact luminous spots. 



