EHYTHM IN NATURE FLATTELY. 395 



graph}', and thence to the study of fish migrations. 10 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 quantity 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 Skagerrak and the Kattegat. As a result of the increased salinity 

 of the Baltic, the herring shoals are enabled to extend their migra- 

 tions to this sea, which is normally closed to them owing to their 

 intolerance of water with a low-salt content. The times of the ap- 

 pearance 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. 11 One of the 

 most convincing pieces of evidence of these climatic cycles is fur- 

 nished by the changes of level which can be traced in the waters of 

 the Lop Nor Basin, a huge inclosed 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 mi- 

 grate and so come into conflict with the peoples of more favored 

 regions. The wave so started, say in the center 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 can not 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. 



The historian, Gibbon, 12 mentions two remarkable facts which 

 tend to show that the climate of Europe in Roman imperial times 

 was much colder than it is now. The Rhine and the Danube were 

 frequently frozen over and capable of supporting the most enor- 

 mous weights, a thing unparalleled in modern times. In the time 

 of Caesar, the reindeer, now confined to the area around the poles, 

 was a native of the Hercynian Forest which then covered a great 

 part of Germany and Poland. To quote Mr. Huntington: 



Apparently the climate of the earth is subject to pulsations of very diverse 

 degrees of intensity and of varying length. The glacial period as a vviiole rep- 

 resents the largest type of pulsation ; upon it are superposed the great pul- 

 sations known as glacial epochs, each with a length measured probably in tens 

 of thousands of years ; their steady progress is in turn interrupted by smaller 



10 Petersson, Otto, Der Fischerbote, III, Nr 7, 8, 9, Hamburg, 1911. 



11 Ellsworth Huntington, The Pulse of Asia, London, Constable, 190 T . 

 13 Gibbon, E., Decline and Fall of the Roman Empire, Chap. I. 



