52 THE CLIMATE OF AUSTRALASIA 



to handle this question has been made by 

 Bruckner of Vienna, whose great book 

 " Klimaschwankungen," the Variations of Cli- 

 mate published in 1891, first placed this 

 subject on a satisfactory footing. 1 * Bruckner 

 was led to his investigation by consideration of 

 the changes that take place in the level of the 

 Caspian Sea. It has long been known that the 

 waters of the Caspian alternately advance and 

 recede. The records go back to the tenth 

 century, and they are complete since early in 

 the eighteenth century. Bruckner found that 

 there was a regular cycle in the rise and fall of 

 the Caspian waters, and that the average dura- 

 tion of a complete cycle was from 34 to 36 years. 

 The dates of the maxima for the Caspian were 

 about 1743, 1780, 1809, 1847, and 1879. 



As the Caspian is an inland sea, its level 

 must depend upon the amount of water supplied 

 by rainfall, and on the rate of its removal by 

 evaporation. The Caspian acts as a great rain 

 gauge for its vast drainage area. A high level 

 of the Caspian, therefore, indicates that the 

 preceding years have been abnormally wet, or 

 that the temperature of the Caspian was low, so 

 that evaporation was slow, or else that both 

 factors worked together. Lakes which have 



*The best summaries of this work in English are in a paper by F. 

 Waldo in the American Journal of Science, ser. 3, vol. xli., 1891, pp. 

 141-151. . There is a longer and admirable summary in Waldo's 

 " Modern Meteorology, "London, 1893, pp. 406-421 ; and some account 

 in the recent translation of Hann's Climatology. (London, 1903). The 

 three books are available for reference in the Melbourne Public 

 Library. 



