On the Pleionian Variations of the Discharge of the Rhine at Basel

M /[ OST of the many researches on climatic variations have been made with the purpose of finding given periodicities. A large number of periods have thus been found; but many if not all of them are problematic, simply becau?e the excess or deficiency of temperature, pressure, or rainfall of a given year can never be observed all over the world. There are always areas of compensation. To ascertain whether temperature was above or below normal on the earth's surface, all available data from all parts of the world have to be taken into consideration and mapped. Only then can a predominance of positive or negative anomalies during a given year be determined. By using this purely geographical method the author was able to show, for example, that the mean air temperature of the continental areas and of a number of oceanic islands was at least 0.3' C. higher during I900 than during I893. It is interesting to notice that these were years of a minimum and a maximum of sunspots respectively. For convenience of expression the author called the areas of positive departures thermopleions or pleions and the areas of negative departures antipleions or meions.' The pleionian centers displace themselves. The pendulation of a pleionian center in North America during the decade I90o-i909 was traced by using overlapping I2-month means and overlapping departure maps.2 For the following decade, i9i0-i919, more extensive researches were made and world maps of temperature3 and atmospheric-pressure anomalies4 were drawn and studied in detail. Aerological observations made at Agra, India, at Paris, and at Lindenberg, near Berlin, also demonstrated the fact that the pleionian temperature variations observed on the earth's surface are reversed at an altitude of I0 to I2 kilometers.' Hence the vertical temperature gradients change, and these changes must depend on, or are the cause of, the formation of pleionian centers. This leads naturally to the study of the exchange of air masses affecting rainfall. To simplify such researches, river-discharge data should be examined first. A series of observations on the water level and discharge of the Rhine, begun at Basel in i8o8 and seemingly perfectly homogeneous up to I933,6 is admirably suited to the purpose. In the course of time certain changes in the river bed have caused changes in the mean level of the waters at Basel.7 Because of this fact, it is preferable, in determining the variations, to take into consideration only the monthly and annual means of the discharge of the river in cubic meters a second. The curves of the annual means and those of the overlapping means for 5, I0, and 20 consecutive years are shown in Figure I. The extreme values are as follows

Environmental Science · Geophysics and Gravity Measurements