[DAWSON] EFFECT OF WIND ON CURRENTS AND TIDAL STREAMS 189 



direction we may term the element of dominant flow which is super- 

 imposed upon the usual tidal elements. It gives rise to much complica- 

 tion as it is large in relation to the strength of the tidal streams, espe- 

 cially at the neaps when they are weak. The tidal streams themselves 

 are also complex in their character, and show at times a marked diurnal 

 inequality which follows the declination of the moon. 



It must not be hastily assumed that the wind is the cause of the 

 dominant flow. There is no evident relation between the direction of 

 this flow and the local wind, to show that one is the cause of the other. 

 The wind would produce primarily a surface drift, whereas the do- 

 minant flow affects the whole body of the water. Examples of a true 

 wind drift have been met with in this strait; but this does not extend to 

 any great depth. It is also to be noted that the dominant flow may 

 continue for a week or more at a time in the one direction, which a wind 

 drift v\'ould not do. 



During both seasons, a careful watcli was kept, to detect any in- 

 fluence of the wind upon the movement of the water ; and the continuous 

 meteorological observations, taken on board, afforded complete weather 

 data for comparison. But it may be stated in general that the effect of 

 the local winds in producing a drift in their own direction is remarkably 

 slight, considering the situation of this strait. In the line of the strait 

 to the westward there is a clear stretch of 470 miles of water across the 

 Gulf of St. Lawrence to the New Brunswick shore; and to the eastward 

 it opens into the Atlantic with no other shelter than what the small 

 island of Belle Isle affords. 



The best indication of the effect of the wind upon the movement of 

 the water is afforded by a difference between the surface current and the 

 under-current, in direction or in the time at which they turn; as it can 

 be stated definitely from the experience gained in this Survey, that the 

 water at a depth of 20 or 25 fathoms at which the under-current was 

 here observed, is unaffected by any storm, at least in the summer season. 

 A departure from the general relations between the surface and under- 

 current as established by these observations, will thus reveal any distur- 

 bance occasioned by wind. 



It was frequently observed, especially in unsettled weather, that if 

 there is a change, it will occur at slack water. For example, when the 

 barometer is low, and a change is to be expected, east wind will come 

 up with the flood. Also a westerly wind will seem to be held back by 

 the flood and will be light and variable till slack water, when it will 

 come out strongly with the ebb. These changes with the tide, in un- 

 settled weather, are exactly similar to those which are so familiar on the 

 Lower St. Lawrence. It would thus appear to be quite as necessary to 



