230 
PROFESSOR FORCHHAMMER ON THE COMPOSITION 
to evaporate than the rivers bring into the sea. My analyses have not given me any 
reason to alter anything in our views of the cause of this difference, nor do I regard the 
single instance of water that is more rich in salts at the surface than in the depth as 
more than a local exception. 
As to the difference between surface and deep water for other substances, I shall only 
remark that the deep water of the Mediterranean contains a remarkable excess of sul- 
phuric acid. The proportion between chlorine and sulphuric acid is 
For the whole ocean . . . 100 : 11-89 
Mediterranean surface . . . 100 : 11-82 
Mediterranean depth . . . 100 : 12-07 
Already in the Straits of Gibraltar the difference has the same character. The proportion is 
For the surface 100 : 11-42 
For the deep water .... 100 : 11-93 
In some places, however, in the Mediterranean the surface-water is richer in sulphuric 
acid than water from the depth ; thus, for instance, the sea between Sardinia and Naples 
had a proportion of 12-55 sulphuric acid in surface-water. 
In the Baltic we have the same phenomenon ; the water from the depth contains 
likewise more salt than that from the surface, but the direction of the currents is the 
reverse. The upper-current goes generally (not always) out of the Baltic, and the under- 
current goes, as it would appear, always into the Baltic. The cause of this great differ- 
ence between the Baltic and the Mediterranean is evident ; the Baltic receives the excess 
of atmospheric water from a great part of Europe. The greater part of Sweden, the 
greater part of European Russia, and a great part of North Germany send their water 
into the Baltic, and the evaporation is comparatively small. Thus the excess must find 
its way through the Sound and the Belts. With the assistance of Captain Prosilius, 
who in the year 1846 commanded the vessel at the station of Elsinore, the surface- 
current was observed on 134 days, from the 27th of April to the 11th of September ; 
of which on 24 days it ran from the north, on 86 days from the south, and on 24 days 
there was no surface-current at all. The quantity of chlorine was determined for every 
sample by titration, and from that the quantity of salt deduced by multiplication with 
the determined coefficient 1-812. The mean quantity of salt for the current from the 
North was 15*994 per 1000; that for the current from the South 11-801 ; that for the 
period when there was no current at all was 13-342. Once a week a sample was taken 
from the bottom, by sending a reversed bottle down to the bottom, turning it there, 
and after having allowed it to stand some time, taking it slowly up. The mean of 
nineteen observations was 19-002 per 1000 salt, which, according to the manner in which 
the samples were taken, is rather under than above the real mean, and proves clearly 
that it is water from the Kattegat which runs at the bottom of the Sound. But we 
have also direct observations of the same fact. Some years ago a steamer was, close to 
Elsinore, struck by another steamer, and sunk a very short time after the collision. 
