[dawsonJ effect of WIND ON CURRENTS AND TIDAL STREAMS 193 



Wind injluence on surface ieinpcvature. — A very noticeable effect of 

 the direct action of the wind upon the water, is a change in the surface 

 temperature. This may occur after a long period of quiet weather when 

 the water has become warm for a few fathoms at tlie surface, resulting 

 in a rapid fall of temperature with the depth. A heavy wind, especially 

 when off shore, may then drive the surface water out to the offing, and 

 allow the cold under-water to come up to the surface. A fair estimate 

 can even be made, by careful comparison, of the depth to which the wind 

 disturbance extends. 



This was well illustrated in Belle Isle strait. In the early part of 

 tlie season when tlie surface temperature is only 35° there is little dif- 

 ference between this and the under-water; but after June the surface 

 laj^er rises to 45° or even 55°, while the deeper water remains almost as 

 cold as before. 



A sudden change in the surface temperature may thus afford a 

 valuable indication of wind disturbance. The best examples of this dur- 

 ing the season of 1906 were as follows: — 



From Red bay to the middle of the strait, the average temperature 

 of the surface water on August 16 was 52°. 7. After the gale of the 17th, 

 the temperature on the following morning between the same points was 

 45°. 2, and on the 20th, the average was still only 44°. 3. This marked 

 change was occasioned by 1,550 miles of N.E. wind, as detailed above. 



From August 18 to September 1 the temperature of the surface 

 water recovered very little, having only risen to 46°, 3 by the 1st. This 

 may have been due in part to the preponderance of westward flow, bring- 

 ing in the colder Atlantic water. Consequently, the temperature of the 

 watei^ in the strait was not appreciably altered by the northeast gale of 

 September 4th. The average temperature across the width of the strait, 

 from Eed bay to a station near the south shore, as obtained on August 

 27, and again on September 5 after the gale, was 45°. 5 on both dates. 



On September 7 and 8 another northerly gale occurred. From the 

 7th at 12 o'clock to the 8th at 11 o'clock, there were 717 miles of wind 

 from ]Sr. and IST. by E., rising to 53 miles an hour as measured in Red 

 bay. The average for the 23 hours was 31 miles an hour. As soon as 

 the wind moderated, on the afternoon of the 8th. it was found that the 

 surface temperature was 2° lower than before for two miles from the 

 north shore, and %° lower at a depth of 5 fathoms. At 10 fathoms 

 there was no change. The average temperature for 9 miles out, to the 

 middle of the strait, was 45°.0. 



There did not appear to be any appreciable change made by the 

 heavy west wind of September 11-12, so far as the observations obtained 

 could indicate. But with the next northerly gale, the difference was 



