312 



NA TURE 



[January 24, 1901 



of rotation in a left-handed direction. It has been proved that 

 there is no great influx of cold water into the Gulf area through 

 Belle Isle Strait, as was formerly supposed. On the contrary, 

 the chief interchange of water between the Gulf and the ocean 

 is at Cabot Strait, the wider entrance to the Gulf south of 

 Newfoundland. 



We cannot enlarge further on these interesting results, as the 

 information as now published is in as concise a form as it can 

 be put. We desire, rather, to draw attention to some points 

 which the investigations themselves emphasise, and which are 

 of general application elsewhere in similar work. 



The most important of these is the relation of the under- 

 currents to the current on the surface. These were examined 

 everywhere, to a depth of 30 fathoms at least, as this depth 

 extends almost uninterruptedly over the whole Gulf area. It 

 may be thought, at first sight, that the direction of the under- 

 current has no bearing upon the movement of the water as it 

 affects navigation. In such a region as the Gulf of St. Law- 

 rence, however, the currents in the summer months are all very 

 tnoderate in their speed, usually ranging from half a knot to one 

 knot per hour ; and their direction on the surface is accordingly 

 much influenced by the wind. It was found in these circum- 

 stances that the movement of the under-current at 20 or 30 

 fathoms often showed more definite characteristics ; as, for 

 example, a tendency to make constantly in some one direction, 

 or to vary with the tide. The wind is thus a disturbing element ; 

 and the under-current, being more in accordance with the normal 

 conditions of the locality, will come up to the surface as soon as 

 the disturbing influences which have been acting on the surface 

 of the water cease to operate. 



It maybe unfortunate, from the point of view of the navigator, 

 that it is the surface of the water to a depth of 5 or 10 fathoms 

 which is so readily and so frequently disturbed ; but, on the other 

 hand, it is clear that it is essential to make a careful investigation 

 of the under-current in order to understand the surface current 

 itself. The study of the under-current is also necessary, if any 

 hope is entertained of arriving at the general circulation in the 

 Gulf or the true relation of its currents to the causes which 

 influence them. 



When a period of some length is considered as a whole, 

 and the under- current is also taken into account, it becomes 

 possible to trace the general circulation of the water ; which 

 depends upon a greater movement in some dominant direction 

 rather than in other directions, when long averages are taken. 



The primary tendency in the surface current is thus to follow 

 the direction which the general circulation has in the locality in 

 question ; but this tendency is disturbed and often overcome by 

 the influence of the tide and wind. The tidal influence shows 

 itself chiefly as a veer in the direction of the current, which is 

 either through a limited range or completely around the com- 

 pass ; and it is also probable that the tides themselves are irregu- 

 lar in some localities, owing to interference. When the wind 

 remains in one quarter and has any considerable strength, the 

 drift which it gives to the surface water soon extends to a depth 

 of five fathoms or more, and its influence thus makes itself felt 

 throughout the thickness of the surface layer which affects ship- 

 ping. As a rule these influences are all acting at the same time ; 

 and it is their combined effect which gives rise to the actual 

 behaviour of the surface current. 



A knowledge of the general circulation is also important to 

 mariners, as it includes all the more constant currents, and it shows 

 the direction which the surface current tends to take when un- 

 disturbed. Although there are few instances of currents in the 

 Gulf area which run steadily enough to be termed constant, we 

 have yet found it possible, from continuous observation or long 

 experience, to arrive at a dominant direction for each locality ; 

 or the direction in which the current runs more frequently, and 

 in which, therefore, the water makes on the whole. 



With regard, also, to the drift of ice as an indication of the set 

 of the current, a superficial view may readily be taken ; but it is 

 here pointed out that to infer correctly the set of the current it 

 is necessary to distinguish between the different kinds of ice met 

 with and their relation to the movement of the surface of the 

 water and to the under-current, respectively. 



This is illustrated by the character of the ice met with in the 

 Gulf of St. Lawrence, which is of three kinds : — (i) Berg ice, or 

 true icebergs, found in the vicinity of the straits opening into 

 the ocean. (2) Flat or pan ice, forming fields or in broken 

 pieces, usually not more than 6 feet in thickness, but sometimes 

 as thick as 10 feet. This often jams or shoves along the shore 



NO. 1630, VOL. 63] 



or between islands, and may form masses 20 feet or more in 

 thickness, but it can never be mistaken for berg ice. (3) River 

 ice, from the St. Lawrence River and its estuary. This is also 

 flat ice, but it can be readily distinguished by its appearance 

 from the Gulf ice. 



The berg ice, from its great depth in the water, will evidently 

 move with the under-current ; and it will not be appreciably 

 affected by the wind. These bergs do not necessarily indicate 

 the direction of the current as affecting shipping, except when 

 the surface current has also the same direction. They show in 

 reality the average direction the current has between the surface 

 and the depth of their draught. This draught is limited to 

 about 30 fathoms by the depth of the Belle Isle Strait. They . 

 are thus of much value as an indication of the general movement - 

 or circulation of the water. 



The relation of the flat ice to the wind and current requires 

 some little consideration. It is, of course, just as true of this 

 ice as of the berg ice, that the greater part is under water ; but, 

 as it is almost always in broken pieces, more or less piled and 

 with upturned edges, the wind has a much greater hold upon 

 it, in proportion to its total weight, than on the berg ice. Even 

 when this is allowed for, its depth in the water still gives the 

 current a greater hold upon it than the wind has. For example, 

 if such ice is drifting with a current in a given direction, and the 

 wind is blowing across that direction at right angles, the ice 

 will seldom be set more than two points, or three at the most, 

 off the true direction of the current. When the ice becomes 

 soggy or water-soaked and loses its edges, as it does later in the 

 spring, it will set still more correctly with the current. 



When the surface current itself is moving in the direction of 

 long-continued or prevalent winds, as it often does in the Gulf, 

 the flat ice naturally follows the same direction too. Also, in | 

 regions where the current is tidal, and the ice in calm weather ' 

 would drift as far in the one direction with the flood tide as in 

 the other direction with the ebb, the direction in which it makes, 

 on the whole, will depend upon the wind. It is probably for 

 these reasons that it is so often said that the ice drifts with the 

 wind ; although this merely expresses the fact, without dis- 

 tinguishing between the relative influence of the wind and the 

 current upon it. 



There is also a direct effect which the ice has upon the 

 strength of the current in regiorrs where the direction of the 

 surface drift is under the influence of the wind. The broken 

 and upturned edges of the ice give the wind a much greater hold 

 upon the water than it otherwise would have. Hence during 

 long continued winds the speed of the current is appreciably 

 greater than if the ice were not present. This is undoubtedly 

 the explanation of the common belief which is expressed by 

 saying that *' the ice makes its own current." It may be well 

 to recall that the weight of the ice itself is the same as the water 

 which it displaces ; and, therefore, the wind has no greater 

 mass to set in motion in producing a surface current than if the 

 ice were to melt and refill the hollow which it makes in the 

 water ; yet the presence of the ice gives the wind a better hold 

 than it would have uponUhe surface of open water free from ice. 

 There' is one condition of the ice which may prevent it from 

 showing correctly the movement of the water. When it is set 

 against an island or headland and packed together for a long 

 distance out, with open water beyond, it may circle round as on 

 a pivot. The outer edge of the pack may thus make a long 

 sweep very different in its path from the true set of the current ; 

 and its movements also become irregular, as vessels caught in 

 such ice which are near together in the evening may be ten or 

 fifteen miles apart in the morning. 



The influence of rivers flowing into such a land-locked area 

 as the Gulf of St. Lawrence is also discussed, with approximate 

 measures of volume which show how small the volume of even 

 such a river as the St. Lawrence is, relatively to the water in 

 motion in a costal current, which is more nearly comparable 

 with an ocean' current. 



The probable balance of flow between the Gulf and the ocean 

 is also explained, but measurements of volume of even an 

 approximate kind are wanting to give precision to the results. 

 The importance of such investigations with regard to the move- 

 ments of fish, which must be influenced by the temperature of 

 density of the water, is also emphasised, in view of the large 

 annual value of the Canadian fisheries. 



The further investigation of the currents has been discontinued 

 since 1896 for reasons of economy; but the tides themselves 

 are receiving careful attention, and already trustworthy tide-tables 



