336 SCOTT’S LAST EXPEDITION 
In the spring of 1911 (September) the sea ice at this point 
was 8 feet 3 inches thick. 
The labour entailed in keeping the holes open was consider- 
able, and the time taken in this work very appreciably curtailed 
the time available for making collections. 
The position chosen was about three-quarters of a mile dis- 
tant from the hut in the strait between Cape Evans and Inacces- 
sible Island, the depth at this point being 100 fathoms. 
Tow-nets of various sized mesh were set at varying depths, 
the current under the ice being sufficiently strong to allow them 
to fish satisfactorily as a stationary net. Very good catches were 
obtained, which were brought back to the hut in Thermos flasks. 
These flasks proved quite invaluable, since catches could be kept 
in perfect condition in the lowest temperatures which otherwise 
would have been ruined by crystals of ice forming and spoiling 
all the more delicate specimens. 
The physical conditions under which these drifting or plank- 
ton organisms exist is of great importance, and observations were 
regularly taken with this end in view. 
The Expedition was fortunate in possessing some very fine 
reversing thermometers made by Richter of Berlin, and these 
were used to determine the temperature of the sea. During the 
winter a reversing water-bottle was used to obtain samples of sea 
water for analysis, but with what success cannot be ascertained 
until the analyses have been carried out. 
During the winter only one sample could be taken each day, 
as the instrument had to be taken back to the hut, thawed out, 
and thoroughly dried. 
Soundings were also taken through cracks and seals’ blow 
holes, and these will be plotted on the charts. 
During the first year a complete record was obtained with 
an automatic tide gauge constructed and looked after by Mr. 
Day. It might be mentioned here that the McMurdo Sound 
tides present some unusual features. Spring-tides and neap tides 
are quite masked by the diurnal inequality of heights, depending 
on the declination of the moon. For example, with high declina- 
tions N. or S. the greatest rise and fall takes place, and there is 
only one high water and one low water in the twenty-four hours. 
But with the moon on the equinoctial there is much less rise and 
fall, and two high waters and two low waters are experienced. 
