The idea of a slow deterioration of the climate due to increasing desiccation is of old lineage and is most likely related to the venerable conception of a bygone golden age. Aristotle even at that early date believed that a gradual arefaction of the Earth took place. In recent times this faith has been particularly fostered by Huntington in a number of treatises where he endeavours to prove that Asia, represented for instance by Palestine, Syria, and Persia, and further Africa and North America are subject to a rapid exsiccation clearly traceable through historic time. The contrary, however, is true about Western Europe. It was often said that Southern Russia in recent times suffered a slow arefaction manifesting itself in the formation of steppes. This led to careful investigations showing the assertion to be erroneous and culminating in the work of Leo Berg. Rather, a slight shifting in the opposite direction is detectable as the forest region has expanded at the expense of the steppes in conformity with the development toward the end of prehistoric time. The renowned American astronomer, the late Dr. Lowell, embraced the idea of increasing aridity which he observed himself in Arizona where his observatory is located. The drying out of Arizona undoubtedly took place in long bygone prehistoric time. The disappearance of a high culture in Syria and Mesopotamia was the result of hostile devastation of their waterworks; a compensation is now offered in the reclamation of the deserts along the Nile, in California and Arizona, and in numerous other places. CHAPTER IV ATMOSPHERE AND PHYSICS OF THE STELLAR BODIES In a certain sense, we are justified in speaking of an atmosphere of suns and stars. These bodies consist mainly of a comparatively dense mass surrounded by a layer of very attenuated gas. The density of our Sun is about 1.4 times that of water. In other stars it is considerably lower, in some cases only a few hundredths of the density of water. This applies particularly to those stars of variable magnitude, the Cepheid type, named after their longest and best known representative, the mysterious star Delta in the constellation Cepheus, and in general to young stars. In any case the stars are gaseous throughout on account of their high temperature. An exception must be made for the clouds of matter precipitated by easily condensed vapours, such as gaseous carbon, which clouds float in the outer strata, and are responsible for the bright astral light.