HYDROGRAPHY. 



145 



year or a certain month, or whether the whole system of oscillations only is due to the effects of the 

 wind. To answer this question in a satisfactory manner, we must know the oscillations that have oc- 

 curred through a longer series of years. It seems to be the case, however, that the line of demarca- 

 tion between the Atlantic-water and the Polar-water is lying more northerly in the spring than in 

 the autumn. 



The fact of the boundary between the cold ice-water and the Atlantic-water not being subject 

 to any change of importance during the course of the year, shows that the resultant of the 

 powers that are trying to dislocate this line of demarcation, on an average only is 

 very small, either because the water on both sides of this line is at rest, or because the momenta 

 have equally large components in opposite directions perpendicular on the boundary line. 



The arrows on the charts of the boundary lines indicate the force and direction of the wind, 

 such as it is noted in the meteorological journals that it principally has been just before the period 

 for which the boundary line has been drawn. Looking at these arrows, we can form an idea 

 of the important part the wind is playing, when the question is about the removal of 

 the boundary line. A prominent south-west wind has the effect of forcing the boundary line to- 

 wards north-east, while by a north-eastwind it is forced towards south-west. The distance the boundary- 

 line is removed, depends as a matter of course on the force of the wind, as well as on the length of 

 time during which it has been blowing in one and the same direction. The direction of the wind 

 during the month of August was changeable to such a degree, that according to the entries in the 

 journals in this respect, it was quite impossible for me to decide how the arrows should be placed. 

 But the other curves indicate the dependence between the place of the boundary and the wind with 

 so great exactness, that we can determine at once, when looking at the shape of the August-curve, 

 how the resultant of the winds that are prevailing in August, ought to be drawn. We have only 

 a small piece of the October-curve, far to the south-westward, which is due to strong north- 

 easterly gales. 



If we take the average temperature for each month of the observations taken in the region 

 of the sea between 65 — 67 Lat. N. as well as those that have been taken between 65° Lat. N. and 

 the boundary, we get: 



65° — 67 Lat. N 



Boundary — 65 Lat N. 



April 



!°28 



May 



2°23 

 i°99 



June 



4°28 

 3°05 



July 



6°i6 

 4°56 



It is a peculiar fact that during the months May, June, and July we meet with 

 lower temperatures in the water between the boundary and 65° Lat N. than between 

 65 and 66° Lat. N. At times the temperature at the boundary goes down as far as i° — 3 . This 

 may be due to the stormy seas round the boundary, as the heated surface-water when it is 

 blowing a gale of wind, is mixed with water from larger depths. This proves also that the water, 

 must be moving in a southerly direction, for in the case of this motion taking place in a northerly 

 direction, we might expect to find the highest temperatures to the southward. 



The Ingolf-Expedltion. I. 2. x 9 



