4 2 4 SCIENCE PROGRESS 



been only recently established. Bruckner, Clough, and others 

 consider that the whole world passes through a climatic cycle 

 once in every thirty-six years. At one end of the cycle the 

 climate of continental regions for a period of years is unusually 

 cold and wet, with relatively frequent storms ; at the other 

 the climate is warmer and drier, with high barometric pres- 

 sure and few storms. The extremes of low temperature are 

 ascribed, somewhat paradoxically it may seem, to periods of 

 maximum solar activity as shown by the number of sun-spots 

 and the rapidity with which they are formed. 



The Swedish hydrographer, Petersson, has published data 

 showing the importance of these climatic cycles to the study 

 of hydrography, and thence to the study of fish-migrations. 1 

 Increased solar activity results in oceanic circulation being 

 more intense. As a result of this, the Baltic, the water of 

 which is normally distinctly brackish, receives a greater quan- 

 tity of salt water from the Atlantic. Owing to the increased 

 oceanic circulation outside, large quantities of water are 

 pumped into the Baltic through the narrow neck between the 

 Skager Rack and the Kattegat. As a result of the increased 

 salinity of the Baltic, the herring shoals are enabled to extend 

 their migrations to this sea, which is normally closed to them 

 owing to their intolerance of water with a low salt content. 

 The times of the appearance of herring in the Baltic thus 

 correspond to the periods of increased solar activity ; in other 

 words, the appearance of herring in the Baltic is a regularly 

 periodic phenomenon. 



A recent American expedition to Turkestan has brought 

 to light regular cycles of wet and dry climate in this region. 2 

 One of the most convincing pieces of evidence of these climatic 

 cycles is furnished by the changes of level which can be traced 

 in the waters of the Lop Nor basin, a huge enclosed area about 

 three times as large as the British Isles, situated in the heart 

 of the Asiatic Continent. The periods of drought result in 

 periods of famine which cause the nomadic races, which live on 

 lands too dry for agriculture, to migrate and so come into 

 conflict with the peoples of more favoured regions. The 

 wave so started, say in the centre of Asia, propagates itself 

 in ever-widening ripples, the most remote of which may even 

 be the cause of a commercial crisis as far away as the United 

 States. Anyone who has lived for a few years in Southern 

 Italy cannot fail to marvel how the old Romans could ever 

 have achieved so much if the climatic conditions were as 

 enervating as they are now. But evidence is forthcoming to 

 show that such was not the case. 



1 Petersson, Otto, Der Fischerbote, III, Nr 7, 8, 9. (Hamburg, 191 1.) 



2 Ellsworth Huntington, The Pulse of Asia. (London: Constable, 1907.) 



