494 E. HUNTINGTON SOLAR HYPOTHESIS OF CLIMATIC CHANGES 



directed mainly to the general scheme of movements, and this has proved 

 so complicated that relatively little is yet known of how the total move- 

 ment of the air varies from year to year. This is true both of such regular 

 phenomena as the trade winds and prevailing westerlies and of such irreg- 

 ular plienomena as cyclonic storms. Such storms prevail to a slight degree 

 in equatorial regions, where they are known as tropical hurricanes, and to a 

 high degree in temperate regions, where they are the element which adds 

 constant variety to the climate of j^orth America, Europe, and Japan. 

 Quantitative measurements of the trade winds and westerlies for a series 

 of years appear never to have been compiled, and the task is sure to prove 

 difficult. Cyclonic storms, however, are recorded with accuracy by the 

 various weather bureaus of the world. This is fortunate, for although 

 among the least imderstood of climatic phenomena, they are among the 

 most important. Each of the two types — that is, tropical hurricanes and 

 tlie ordinary storms of the temperate zone — seems to show a close con- 

 nection with sun-spots. Tropical hurricanes have been investigated in 

 the Atlantic Ocean by Pocy and Fassig and in the Indian Ocean by Mel- 

 drum. Their number and intensity vary in harmony with the number of 

 sun-spots. Wolf^^ has compared the number of hurricanes with the num- 

 ber of sun-spots and gets the interesting result, shown in Table 2. Here 

 we seem to liave an unmistakable relationship : 



Table 2 

 Number of hurricanes per year Relative sun-spot numbers 



1 and 2 : 17 



3 59 



4 62 



5 . 70 



6 and 7 80 



8 88 



Continental versus marine climates in Europe during the sun-spot 

 cycle. — In temperate latitudes cyclonic storms are far more numerous 

 and important than within the tropics. In fact they are the controlling 

 element of the climate, and any changes which have occurred in the past 

 must be closely associated with them. Unfortunately, the storms of Eu- 

 7*ope can not easily be investigated as yet, except for a short series of 

 years, for the barometric records have not been charted in such a way as 

 to show their movements. Later, in connection with the storms of Amer- 

 ica, we shall consider those recorded in Europe. For the present, how- 

 ever, let us turn to a new line of evidence which sheds light on climatic 

 changes in quite a different way. In "The Climatic Factor" much space 



w J. Hann ; ^llmatolo^lQ, vol. 1, p.- 360. 



