806 SCIENCE. 
a mean velocity of 1.06 decimeters per sec- 
ond at the surface, and 0.20 decimeter at 
the bottom in 55 m. depth, and an ingoing 
current fromS. W., to W.S. W. with 2.16 
decimeters velocity at the surface and 0.37 
decimeter at the bottom. With strong 
winds the currents extended all the way to 
the bottom ; with feeble winds still water is 
found at the bottom. Contrary local winds 
often produce still water or drift currents at 
the surface, when the main current is out- 
going, but the stronger inflowing current is 
seldom stopped by contrary winds. 
The salt determinations in the northern 
Baltic show a surface layer of 15-20 m. 
deep with an average saltness of 5.6 to 5.7 
grammes of salt to the liter; between 20 
and 45 m. a mixed layer of 6 to 7.3 
grammes; and between 45 and 55 m. a 
nearly homogeneous bottom layer of 7.5 to 
7.7 grammes of salt, which shows scarcely 
any variation during different seasons. 
This bottom layer also shows but slight 
changes of temperature ; between June 11 
and August 16, 1877, the temperature rose 
from 0°.5 to 1°.6, while at the surface dur- 
ing the same time it rose from 4°.6 to 17°.5. 
Thus far I have followed Dr. Cronander, 
but I feel tempted, before concluding, to 
make a few remarks concerning the conclu- 
sions reached, and also to apply the results 
obtained towards the explanation of some 
of the more prominent ocean currents, which 
he has refrained from doing. 
In the estimate of the Baltic current, 
based on difference of level between the 
Baltic and North Sea, a uniform slope of 
1: 3000000 from the head of the Baltic to 
the North Sea has been assumed. It ap- 
pears quite probable to me that,on account of 
the obstruction which the narrow and shal- 
low passages interpose to the free passage of 
water between these two seas, the surface of 
the Baltic will be nearly on a perfect level 
and that at its juncture with the North Sea 
there will be a much greater difference of 
[N. S. Von. X. No. 257. 
level than that indicated by a slope of 
1: 3000000 and quite sufficient to produce 
perceptible currents in the Sound and Great 
Belt. In a critical examination of the cur- 
rents in these two passages, I think the 
tidal currents should have received some 
consideration. The rise of the tide in dif- 
ferent parts of the Baltic furnishes the 
means of determining the strength of these 
currents; and, however small it may be, 
the figures should have been produced just 
as has been done with the so-called Baltic 
Current. Furthermore, I am willing to 
admit that Dr. Cronander’s observations 
prove that in the open Baltic the currents 
move in obedience to laws identical with 
those governing the flow of rivers; but in 
the Sound and Great Belt the direction and 
flow of currents are so greatly modified by 
contraction of the channels, that a current, 
which in the open Baltic or North Sea 
might be considered a mere drift current, 
could be easily changed into a veritable 
river current. 
The equatorial currents appear to me to be 
fair examples of surface currents which de- 
rive their strength solely from the action of 
the trade winds. Unfortunately, deep-sea 
current observations are not at hand, but, if 
the above supposition holds, their depth 
cannot be very great. The current through 
the Strait of Yucatan, which at the surface © 
surpasses the strength of all the Gulf 
Stream waters, is assumed to be due to the | 
partial barrier, namely, Yucatan and Cuba, 
between the Caribbean Sea and the Gulf of 
Mexico. According to Pillsbury’s observa- 
tions, I estimate its depth at 200 fathoms. 
The undercurrent from the Gulf of Mexico, 
which I am led to believe exists, from com- 
parison of the quantities of water that enter 
the Gulf and leave it through the Strait of 
Florida, may possibly be explained upon 
the same grounds as those undercurrents 
occasionally met with in the Great Belt, 
viz., an effort towards the restoration of 
