Draw a circle round the point of angular radius ten degrees (i.e. set the compass to cover ten degrees of latitude) and divide this into two halves by a line passing from north to south through the centre. By means of squared tracing paper, or otherwise, measure: (_a_) the amount of ice in the whole circle; (_b_) the amount of land in the western half; (_c_) the amount of land in the eastern half. (_a_) is expressed as a percentage of the area of the whole circle; (_b_) and (_c_) as percentages of the area of a semicircle. The term “ice” includes ice-sheets such as that of Greenland or Antarctica, and also frozen sea or sea closely covered by pack-ice; the latter figure may vary in different months. The temperature in January or July is then calculated from the following formula: Temperature = basal temperature + ice coeff. x per cent. of ice + land west coeff. x per cent. of land to west + land east coeff. x per cent. of land to east. The basal temperatures and the appropriate coefficients are given in the following table. In calculating the effect of a given slight change of land and sea distribution, it is not necessary to employ the basal temperature. Instead the equation can be treated as a differential, and the change of temperature due to the change of land and ice calculated from the figures in columns 3 to 5. The figures are given in degrees absolute, 273°0 = 32° F. To convert differences to Fahrenheit, multiply by 1°8. ---------+-------------+----------+-----------+----------- Latitude.| Basal Temp. |Ice Coeff.| Land, | Land, |(Water Zone).| |West Coeff.|East Coeff. ---------+-------------+----------+-----------+----------- Jan. | a. | | | 70 N. | 298.8 | -0.49 | -0.43 | -0.20 60 | 277.4 | -0.07 | -0.31 | -0.01 50 | 276.8 | -0.09 | -0.29 | 0.09 40 | 282.5 | -- | -0.17 | 0.04 30 | 289.6 | -- | -0.08 | 0.03 20 | 294.2 | -- | -0.01 | -0.01 10 | 298.6 | -- | -0.01 | 0.03 0 | 299.3 | -- | 0.01 | 0.00 10 S. | 298.2 | -- | 0.04 | -0.01 20 | 296.2 | -- | 0.07 | 0.00 30 | 293.5 | -- | 0.06 | 0.03 40 | 289.3 | -- | 0.09 | -0.03 | | | | July. | | | | 70 N. | 279.3 | -0.16 | 0.02 | 0.02 60 | 280.7 | -- | -0.01 | 0.11 50 | 285.8 | -- | 0.04 | 0.06 40 | 291.1 | -- | 0.05 | 0.07 30 | 296.8 | -- | 0.08 | -0.01 20 | 297.6 | -- | 0.07 | 0.02 10 | 298.8 | -- | 0.03 | -0.01