To state an example: The positions of Berlin and London are such, that the summer-heat and the winter-cold ought to be equal in both places. But because England is an island in the ocean, that is, surrounded by large masses of water, the evaporation of water is in London much greater; hence the summer there is cooler. For the same reason rain and fog are much more frequent there, and the winter, consequently, is less severe. In the course of this work we shall see how similar conditions have very great influence upon whole countries, and therefore often cause, contrary to the rule, cold summers and warm winters. CHAPTER IX. RULES ABOUT THE WEATHER, AND DISTURBANCES OF THE SAME. If we cast a glance upon the phenomena of our atmosphere, we find that they are indeed computable, and that the weather in general may be foretold, even for large countries, with some degree of certainty. Nay, there are countries where the weather is not variable at all, but changes at regular periods and according to fixed rules. In countries near the equator, where the sun's heat is very strong, heat, calm, and dryness prevail during the summer-time. This state of the atmosphere continues uninterruptedly until winter; nor can there be any frost there in winter, because even then the sun's rays fall with but little obliquity upon the surface of the earth. But inasmuch as the sun no longer heats the earth to the same degree, the air ceases to retain the same amount of heat, and as a great deal of cold air is constantly passing in from the poles, the vapor spoken of above is, at that season of the year, changed back into water. Thus, winter there is merely a long, uninterrupted rainy season. We see that for the warmer countries the rules of temperature are pretty constant and sure; there one is not surprised by irregularities of weather such as occur with us. Summer brings heat, calm, and dryness; winter, east winds, thunder-storms, and continual rain. The rain once ceasing, the sun reappears in a few days, and everything begins to bloom again. This holds good only for the countries near the equator. The further you go towards the poles, the more varied become summer and winter, the length of day and night, heat and cold, and consequently, also, the condition of the atmosphere and of the weather proper.