34 F. L. Ekman, 



fed from the evaporatiug basin itself, tlms discharging a quantity of 

 water corresponding to the surplus carried thither by the surface-stream. 

 This undercurrent penetrates trough the basins mouth into the ocean 

 and there sinks in consequence of its greater weight. Provided the di- 

 mensions of the mouth afford sufficient room for this double circulation, 

 the specific weight of the water in the basin can probably not attain 

 such an amount, that a real surplus of hydrostatic pressure should take 

 place from that side, were it not helped by the excess of water carried 

 thither by mechanical reaction. 



This appears to me likely to be the true explanation of the 

 double stream in the strait of Gibraltar. The theory, which attempts to 

 account for the under-current exclusively by the greater specific gravity 

 of the Mediterranean's water, is besides destitute of the necessary foun- 

 dation, as long as we know nothing about the relative height of the 

 levels. The chief difference between the currents of Gibraltar and the 

 Sound appears to me to be, that in the first case the surface-current 

 flows from a locality with constant level to one, where the level is al- 

 ways sinking, whereas in the second case it flows from a region, where 

 the level is always rising, to one, where it is constant. 



In further confirmation of this view I may be allowed to adduce 

 an experiment, which I made to convince myself, that a double stream 

 of this kind may be produced independently of the specific weight of the 

 water-strata. In a box of 12 decimetres length and V/^ decimetres broad 

 and deep I set up for the purpose a vertical partition in the middle, 

 in the upper part of which was an opening, about ^/^ decimetre broad 

 and 1 dec. deep. The box was filled with fresh water and a stream, 

 yielding only about- 100 cub. cent, per minute, was conducted to one end 

 of the box behind a pack of hards there put in, which caused the stream 

 to be uniformly distributed; at the other end of the box the water esca- 

 ped through a hole at the surface. Then on immersing a glass rod, 

 wetted with a solution of aniline, perpendicular to the bottom of the 

 box, I could by the diffusion of the colour observe, the slight motion of 

 the water at any depth. When the rod was placed at the opening in 

 the partition, a constant under-stream was observed to flow from the di- 

 vision of the box, from which the water escaped, to that, into which it 

 was admitted. This stream was then analogous to that, which exists 

 between the Mediterranean and the ocean, with merely the difference, 

 that in this case the water flowed instead of evaporating from the sur- 

 face, and that no salt was present. 



