Haddon, A. C., “The wanderings of peoples.” Cambridge University Press, 1919.
APPENDIX
THE FACTORS OF TEMPERATURE
To calculate the probable temperature of January or July at any point, the following procedure should be adopted:
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.