230 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
tion of the density, salinity, and amount of oxygen of the sea water. 
Speed was essential when the water samples were taken in winter. 
After the water bottle was hauled up, it had to be detached from the 
wire as quickly as possible and the observer had to run headlong on 
board with it to prevent the contents from freezing. 
The water bottles were emptied in the laboratory, where samples 
for the various investigations were taken to be examined. The 
specific gravity, for instance, was determined with a high degree of 
accuracy by using Nansen’s hydrometer of total immersion, and the 
amount of chlorine from which the specific gravity could be com- 
puted independently was determined by careful titration. Sys- 
tematic differences amounting to five in the fifth decimal between 
the computed and observed densities indicate that the composition of 
the sea water is altered by freezing. Chemical analyses of the 
samples we are bringing home may throw light on the character of 
these changes. 
We found, furthermore, that over a large part of the shelf the 
density of the sea water remained constant to a depth of 20 fathoms, 
where a sudden increase took place. The lighter surface water was 
separated from the heavier bottom water by a marked surface of dis- 
continuity, which is of the same importance to the currents in the 
sea as is the surface of discontinuity in the air above the ice to the 
air currents or winds. 
We had no biologist on board, and I am therefore unable to give 
any account of the life in the sea. We did, however, collect samples 
of plankton and specimens from the bottom of the sea, which we have 
preserved and are bringing home for further study. 
The investigation of the tidal phenomena has taken much of our 
time and brought interesting results. ‘The tides were recorded con- 
tinuously at Bear Islands by a tidal gauge constructed on board. 
On the shelf the range of tide and time of high water were deter- 
mined at several stations by means of direct soundings, and the tidal 
currents were measured or recorded continuously. At first we used 
the current meter constructed by Ekman, but soon found that this 
delicate instrument was too difficult to handle in low temperature. 
The moment it was hauled up for reading it became coated with ice 
and had to be taken indoors and heated before it could be lowered 
again. We needed an instrument which could be left lowered for 
weeks, recording the currents under the ice electrically in the labora- 
tory. Mr. Dahl and I succeeded in designing an instrument of this 
kind, which recorded direction and velocity of the currents by means 
of a single electric circuit, but I can not enter upon the details of 
construction. Two types were developed, one of which was sus- 
pended on a single wire and recorded the direction by means of a 
compass needle, and another which was suspended in a bifilar frame 
