91 



miles in 30 days. This indicates an easterly current between these 

 two points of 0.8 to 0.9 knot per hour. The drift track is shown on 

 chart ''C." From July 3 to 4, when under observation of the patrol, 

 she traveled eastward at the very rapid rate of 2.5 knots per hour. 

 This high-drift rate was certainly not due to favoring A\dnds, both 

 because little pf the derelict was exposed above the surface and be- 

 cause light southerly airs prevailed during this period. 



The appearance of a berg at night in the light of a full moon on 

 April 30 was interesting. The sky and the moon were entirely covered 

 by a thin hhn of cirrus stratus clouds, when a berg was sighted 8 miles 

 away, bearing 330°, true; the moon at the time bore 165° and its 

 altitude was 35°. This was about the maximum of visibility since 

 the berg was barely discernible as a white, luminous spot. It assumed 

 a glistening white appearance at 5 miles, plain to the naked eye, and 

 similar to a berg in the sunshine. The patrol ship passed close to the 

 berg and then changed course to 0°. After proceeding 8 miles, the 

 berg could be seen as a mere white place on the horizon. 



The limit of visibility of a berg, with clear atmospheric conditions at 

 night in the moonlight, depends upon (a) the altitude of moon, 

 (h) the size of the moon, and (c) the relative position of moon, 

 berg, and ship. Other tilings being equal, the limit of visibility is, of 

 course, directly proportional to the size of the moon and its altitude. 

 Another important factor is represented by (c). If the berg is be- 

 tween the ship and the moon, the likelihood of seeing it is less than 

 if the berg and moon bear in widely different directions from the ship. 

 The effect of position (c) is minimized as the altitude of the moon 

 increases and vice versa. A low moon, behind a berg, gives the 

 poorest conditions for visibility. The experience with the berg just 

 discussed shows that given a full moon, at an altitude of 35°, cov- 

 ered by a thin film of cirrus stratus clouds, a berg is clearly visible 

 to the naked eye at a distance of 5 miles, irrespective of the relative 

 positions of berg, moon, and ship. 



Temperature. — The cold water area, as shown on the surface tem- 

 perature chart ''N," was much less extensive in July than in June, 

 due to the prevailing southerly winds, which blew the warmer surface 

 layers northward, oveiTiding this area. The same condition was ob- 

 served in 1912, as shown by charts "O" and "P/'i^ bringing out the 

 fact that warm surface water flooded northward and restricted the 

 surface signs of the Labrador Current to a small tongue extending 

 only 60 miles southwest of the Tail. Tliis same seasonal change, 

 which is characteristic of the approach of the end of the ice season, 

 was underway July 6 to 10, 1923. Bergs which might be borne 

 southward around the Tail at this time would tend to remain north- 

 's 1922. Smith, Edward H.: International Ice Observation and Ice Patrol Service, U. S. Coast Guard 

 Bulletin No. 10. Charts "O" and "P." 



