THE EARTH AXD THE SUX 493 



presently show, seem to indicate an even closer coincidence between solar 

 activity and the occurrence of earthquakes and volcanic eruptions. 



Lockyer, Bigelow, Bruckner, C lough and others have described 

 climatic cycles averaging 3, 11, 36 and 300 years in length, all closely 

 coincident with variations in solar activity. The 36-year cycle of 

 Bruckner is the best established and most easily recognizable. It is 

 now accepted by the majority of meteorologists. It appears to pertain 

 to the continental regions of the earth as a whole, although there are 

 certain parts of the land close to the sea where the changes are the 

 reverse of those in the interior. As to the seas data are not available. 

 In continental regions the temperature is comparatively low at one 

 extreme of the cycle; storms, clouds and precipitation are relatively 

 abundant; storm-tracks of temperate regions approach the equator; 

 snow lies long in winter; glaciers and rivers increase in size; lakes, 

 especially those having no outlets, stand at a high level; and vegeta- 

 tion and animal life are appropriately influenced, as is evident from 

 the time of the ripening of crops, and the expansion of irrigated areas 

 in arid regions. These conditions prevail regularly at an interval of 

 a few years after periods of exceptional activity in the sun. During 

 the period of activity the 11-year sunspot cycle is reduced to 9 or 10 

 years, and there are other signs of unusual movement in the solar 

 atmosphere. The other extreme of the Bruckner cycle follows a period 

 of comparative inactivity in the sun, and is characterized by climatic 

 phenomena the opposite of those just described. Meteorologists are not 

 yet agreed as to the cause of the climatic cycles, but it seems to be well 

 established that the)' are somehow connected with the sun. 



In regard to the relation of solar activity to earthquakes and vol- 

 canoes, there is at present no agreement among students. On the whole, 

 the evidence has seemed to most investigators to indicate that there 

 is no relation. This appears to be largely due to the use of individual 

 cases instead of averages, and to an attempt to find a coincidence be- 

 tween telluric activity, manifested in earthquakes and volcanoes, and 

 maximum epochs of solar spottedness. Jensen, however, who has taken 

 up the subject in a comprehensive fashion in volume thirty-six of the 

 " Proceedings of the Boyal Society of Xew South Wales," has come to a 

 different conclusion. He has compiled a list of notable earthquakes 

 and volcanic eruptions from 1783 to 1902. Each occurrence has been 

 assigned a value of one, two, three or four, according to its severity, and 

 all the earthquakes and eruptions for the whole series of years have 

 been plotted as shown in Fig. 1. Having in this way obtained a 

 graphic representation of the intensity of telluric activity in each year, 

 Jensen added a curve showing the occurrence of sunspot maxima and 

 minima. An inspection of the diagram thus obtained shows that 



