F Waldo — Bruckner^s Klimaschwankungen. 147 



For the present century more exact dates can be assigned to 

 the times of actual maximum and minimum of rain-fall and 

 they are as follows : 



1815 18G1-65 



1831-35 1876-80 



1846-50 



From this it would appear probable that we are about to" 

 enter upon another period of very low rainfall about 1890-95. 



Atmospheric Pressure. — The study of synoptic charts, and 

 the theoretical studies of Ferrel, Guldberg and Mohn and 

 others, have shown us the controlling influence of the distri- 

 bution of air pressure on climate for short periods and the 

 desirability of a comparative investigation for long periods was 

 unquestioned ; but the data for such a work were in such a 

 condition that the chance was exceedingly slight for obtaining 

 any results deserving of notice. Bruckner has boldly attacked 

 the problem, however, and has deduced some conclusions which 

 the agreement of so many different series of observations for- 

 bid our criticizing as being based on deviations within the pos- 

 sibility of errors for single or a few places of observation. These 

 investigations are based mainly on the matter presented by 

 Hann in his recent great work on the " Air Pressure in 

 Europe ;" and in fact without this work as a basis, Bruckner 

 would have been obliged either to forego this investigation or 

 else to spend a year or so in the critical discussion of his prelim- 

 inary data. As it is, his results refer mainly to Europe, and 

 cannot be made to include other continents until some one has 

 done for the observations of the air pressure on them what 

 Hann spent two years (and many more in preparation) in doing 

 for Europe. 



The oscillations of the air pressure are discussed by Bruck- 

 ner under two heads : those of the annual averages and those 

 of the seasons. The table on the following page shows the 

 lustra deviations of the air pressure in millimeters from the 

 average for 1851-1880, and also the rain-fall in per cents. 



We see here that for the North Atlantic Ocean a relation 

 exists the reverse of that in Central Europe. 



The following arrangement shows the pressure variations in 

 winter and summer for the dry and wet periods : 



Relative Pressure. 



North Atlantic. W. and Central Europe. E. Europe and N. Asia. 



Winter. Summer. Winter. Summer. Winter. Summer. 



Dry period, Lower. Higher. Higher. Higher. Higher. Lower. 



Wet period, Higher. Lower. Lower. Lower. Lower. Higher. 



The discussion of these oscillations shows that for the dry 



period as compared with the rainy period there exists : (1) A 



Am. Jour. Sci. — Third Series, Vol. XLT, No. 242.— February, 1891. 

 10 



