The Geographical Journal (Journal of the Royal Geographical Society): Volume XII, No. 2 [‎261v] (25/154)

116 THE ANNUAL RANGE OF TEMPERATURE IN THE SURFACE WATERS OF THE
presented to the naturalist. In the tropics a marine animal—a cope-
pod or isopod, for instance—lives constantly in water at a temperature
of about 70° Fahr.; in the polar seas, a similar animal lives as constantly
in water at a temperature about zero. What is the difference in the
rate of metabolism, length of life, rate of reproduction, and general life-
history of the two animals ? There seems to be little doubt that a
satisfactory reply to these questions would explain many of the observed
differences between polar and tropical faunas.
The above and some other allied considerations, together with the
desirability of having a more precise knowledge of the variations in the
range of temperature in different regions of the ocean, induced me some
years ago to attempt the preparation of a map showing the annual range
of temperature in the surface waters of the ocean within every two-
degree square on the water surface of the globe; for it seemed that a
comparison of the range of temperature in different places at the surface
of the ocean might possibly show an intimate connection with other
oceanographic phenomena.
2. Preparation of the Range-Map from Temperature Observations
in Every 2 ° Square.
A first attempt was made by using the Charts showing the surface
temperature of the Atlantic, Indian, and Pacific Oceans, published by the
Meteorological Council in 1884. In these charts the mean temperature
and range are given for the four different months, February, May,.
August, and November, as recorded within each 2° square throughout
the three oceans; in some localities numerous observations made it
possible to give the results within smaller areas. In order to arrive at
the extreme annual range within each 2° square, the figures were used
in the following manner : Taking the map for February, the maximum
and minimum temperatures for any particular 2° square in that month
were obtained by adding half the given range to the mean temperature
for the maximum, and by subtracting half the given range from the
mean for the minimum. This operation was repeated with the maps for
May, August, and November, and the four maxima and the four minima
were entered on specially ruled paper. The extreme range shown bj 7
these four sets of figures was laid down on a blank map as the approxi
mate annual range of surface temperature in each 2° square, and lines
were drawn for intervals of ICC Fahr. of range of temperature, in the
same manner as the lines on the map accompanying this paper.
A map constructed on this principle was exhibited at a lecture, on
the structure, origin, and distribution of coral reefs and islands, delivered
before the Royal Institution of Great Britain, in London, on March 16,
1888, with special reference to the range of temperature within the
coral-reef regions. On careful consideration this map was not published.
The method was rejected as unsatisfactory, because the given mean.