Note 25 — Chapter II · OCEANS-CURRENTS IN RELATION TO THE DISTRIBUTION OF HEAT OVER THE GLOBE.
Reading edition
The mean temperature of the equator, according to Dove, is 79°·7, and that of the north pole 2°·3. But as there is, of course, some uncertainty regarding the actual mean temperature of the poles, we may take the difference in round numbers at 80°.