volume of water.  The Frithjof section in particular seems to show that the vertical circulation in these regions reaches to a depth of 500 or 600 metres at the close of the winter.  If we consider, then, what must happen over a bank in the ocean, where the depth is less than this, it is obvious that the vertical circulation will here be prevented by the bottom from reaching the depth it otherwise would, and there will be a smaller volume of water to take part in this circulation and to be mixed with the cooled and diluted surface water.  But as the cooling of the surface and the precipitation are the same there as in the surrounding regions, the consequence must be that the whole of this volume of water over the bank will be colder and less salt than the surrounding waters.  And as this bank water, on account of its lower temperature, is heavier than the water of the surrounding sea, it will have a tendency to spread itself outwards along the bottom, and to sink down along the slopes from the sides of the bank.  This obviously contributes to increase the opposition that such banks offer to the advance of ocean currents, even when they lie fairly deep.

These conditions, which in many respects are of great importance, are clearly shown in the two Fram sections and the Frithjof section.

The Northern Fram section went from a point to the north-west of the Rockall Bank (Station 15), across the northern end of this bank (Station 16), and across the northern part of the wide channel (Rockall Channel) between it and Scotland.  As might be expected, both temperature and salinity are lower in this section than in the southern one, since in the course of their slow northward movement the waters are cooled, especially by the vertical circulation in winter already mentioned, and are mixed with water containing less salt, especially precipitated water.  While in the southern section the isotherm for 10deg.  C. went down to 500 metres, it here lies at a depth of between 50 and 25 metres.  In the comparatively short distance between the two sections, the whole volume of water has been cooled between 1deg. and 2deg.  C. This represents a great quantity of warmth, and it is chiefly given off to the air, which is thus warmed over a great area.  Water contains more than 3,000 times as much warmth as the same volume of air at the same temperature.  For example, if 1 cubic metre of water is cooled 1deg., and the whole quantity of warmth thus taken from the water is given

[Fig. 4. —­ Temperature and Salinity in the “Fram’s” Northern Section, July 1910]

to the air, it is sufficient to warm more than 3,000 cubic metres of air 1deg., when subjected to the pressure of one atmosphere.  In other words, if the surface water of a region of the sea is cooled 1deg. to a depth of 1 metre, the quantity of warmth thus taken from the sea is sufficient to warm the air of the same region 1deg. up to a height of much more than 3,000 metres, since at high altitudes the air is subjected