Although the activities of the Mannheim society came to an end in the troublous days of the French Revolution, the records that it had collected served as the groundwork for fruitful studies during the next generation. There are two distinct uses that can be made of statistics of this sort. First, they can be digested in such a way as to bring out the characteristic features of the climate at each of the localities included in the collection, and likewise to illustrate the distribution of climates over the globe. Second, the data for individual days from the various stations can be charted separately, so as to illustrate the _instantaneous_ distribution of barometric pressure, wind and weather, and, by a comparison of the charts for successive days, to provide a sort of moving picture of the atmospheric machinery in operation. Charts based on approximately simultaneous observations showing the state of the atmosphere at a particular moment of time over an extensive area of the earth are called _synchronous charts_, or sometimes _synoptic charts_, though the latter term is also applicable to charts showing average values for a particular month, year, etc. Synchronous charts, as used nowadays for the purpose of making forecasts, are prepared from data collected by telegraph; but the same kind of charts can be prepared in a more leisurely manner from the statistics gathered at any previous time, and such charts were frequently made for the purpose of study before the days of telegraphy. The pioneer in such undertakings was the German physicist, H. W. Brandes, who, about 1820, utilized the observations collected by the Meteorological Society of the Palatinate, together with some others, in compiling a series of daily synchronous charts of Europe for the year 1783.