SCIEXTIFIC r.ESVLTS 127 



From our own observations at sea in the ice regions we can remark 

 that the circulatory effect of icebergs is rehatively so weak, and the 

 many temperature variations in the surface waters so fluctuating that 

 even the most sensitive thermal recorder can hardly be expected to 

 -( rve as a relial)le iceberg detector. It is ho})ed. however, that purely 

 from the standpoint of scientific interest, information regarding the 

 circulation induced by melting icebergs Avill soon be more firmly 

 established. 



Visibility and Mihage 



Icebergs floating far out from shore in Davis Strait and in the 

 North Atlantic are sighted at various distances depending upon the 

 state of visibility, height of the berg, and of the observer.*'* Smith's 

 (192Ta) investigations in the ice regions south of Newfoundland state 

 that bergs can be seen on a very clear day by a crow's-nest lookout at 

 12 to 15 miles, and they have been picked up under excellent visibility 

 a maximmn distance of 20 miles by a masthead lookout.*'^ The bridge 

 usually sights a berg on ordinary days at 10 to 12 miles, in clear 

 weather, but with a low lying haze around the horizon, the tops of 

 bergs have been seen 9 to 11 miles. There is a tendency to over- 

 estimate the distance, believing that one can see farther than is actu- 

 ally the case. In a dense fog a berg can not be seen more than 100 

 yards ahead of the ship, where it takes form as a luminous white 

 mass if the sun is shining, otherwise it first appears close aboard as a 

 dark somber shape. In a light, low fog an observer can see ice first 

 near the surface of the sea. tlie initial signs being the lapping of the 

 water on its base. A V)erg may be seen at a consideral)le distance on 

 a clear, moonlight night, how far depending upon the altitude and 

 size of the moon, and on the relative position of the moon, berg, and 

 ship. Given a full moon at an altitude of 35°, a berg; can be discerned 

 at a distance of 8 miles, and is plainly visible to the naked eye as a 

 glistening, luminous spot at 5 miles. 



Mirages at sea often create fantastic berg shapes, the images 

 appearing inverted and much larger than the actual berg proves to be 

 when alongside. Each new berg sighted afar looks much larger than 

 its predecessors nearer to, but upon closer approach both images 

 gradually shrink; the upper snaps off and disappears in space, while 

 the lower contracts until correct proportions are restored. Berg 

 mirages are very frequent in the waters around New^foundland, where 

 the plane of atmospheric discontinuity is well developed in summer, 

 a luindred feet or less above the water, the stratification of the air is 

 sometimes so sharp that berglike reflections rise and fall even with 

 the motion of the ship on the swell. There is a record of an iceberg 

 the image of which was sighted over 20 miles away in the mixed 

 Avaters south of Newfoundland; it first appeared as three bergs, one 

 set upon the other, Avith the mirage continually changing shape as it 

 was approached. An ice blink is a common phenomenon attending 



«* Due to the flat opaque whiteness of icebergs and their consequent poor ability to re- 

 flect any particular color, a pair of binoculars fitted with amber sun shades are found a 

 great help in scanning the horizon. Amber-colored spectacles for navigators in ice regions 

 are also recommended. , ^ ^ 



<^Zeusler (1925, p. 37) reports an incident where a berg was sighted at a maximum 

 distance of 36 miles. Commander Roach from the cutter Modoc in May. 1930, reported 

 sighting a berg under conditions of unusual refraction at a distance of 50 miles. 



