The main object of this book is to explain the use of the weather map, where it can be of use, for the purpose of making predictions. The kinds of weather that can be foretold are the great changes, and these are the ones most interesting to know. Successful continuous predictions for every day are not possible. A fall of temperature as great as 40 degrees can be foreseen to a certainty for most parts of the country east of the Mississippi River. The north-east rain storms along the Atlantic coast can be successfully predicted in most cases. Floods along the lower Ohio and Mississippi rivers can be foreseen from one to three weeks in advance of their occurrence, and the height the water will reach can be assigned within a foot or two. Rain occurs, as a rule, with the areas of low air pressure that cross the country from west to east and from south-west to north-east. The average direction and rate of motion of these areas are known, but they are subject to many irregularities. Rain can in most cases be inferred for regions over which the areas are likely to pass. At times, however.