-------+-------------------------+-------------------------- | Aphelion December. | Aphelion June. +-------------------------+-------------------------- | Winter. Summer. Year. | Winter. Summer. Year. +-------------------------+-------------------------- | °F. °F. °F. | °F. °F. °F. N. 60° | -9 +15 -1 | -5 -4 -1 30° | -13 +13 -2 | +1 -8 -2 Equator| -8 +4 -2 | +1 -6 -2 S. 30° | -6 +1 -2 | +3 -5 -2 60° | -2 -1 -1 | +1 -2 -1 -------+-------------------------+-------------------------- Spitaler claims that these differences are sufficient to cause a glacial period in the hemisphere with winter in aphelion, but from this point his theory departs widely from Croll’s. During the long severe winter great volumes of sea water are brought to a low temperature, and, owing to their greater weight, sink to the bottom of the ocean, where they remain cold and accumulate from year to year. But the water warmed during the short hot summer remains on the surface, where its heat is dissipated by evaporation and radiation. Thus, throughout the cold period, lasting about 10,000 years, the ocean in that hemisphere is steadily growing colder, and this mass of cold water is sufficient to maintain a low temperature through the whole of the following period of 10,000 years with winter in perihelion, which would otherwise be a genial interval. In this way a period of great eccentricity becomes a glacial period over the whole earth, but with crests of maximum intensity alternating in the two hemispheres. Unfortunately the numerical basis of this theory is not presented, and it seems incredible that a deficiency of temperature could be thus maintained through so long a period. Further, the difficulty about chronology remains, and the work brings the astronomical theory no nearer to being a solution of the Ice Age problem than was Croll’s.