SUNSPOTS AND VOLCANIC AND SEISMIC PHENOMENA. 43 



just stated, and similarly, seismological and volcanic dis- 

 turbances might be expected to increase in number and 

 violence in sunspot maximum years. 



On the other hand, in regions like parts of North America, 

 Australia, Central Asia and the European continent, where 

 elevation of land by rise of isogeotherms has ceased, and 

 any changes of level may naturally be ascribed to isostasy, 

 winter earthquakes are commonest. Denudation and the 

 consequent unloading hasten secular cooling, and contrac- 

 tion goes on most rapidly in periods when least solar energy 

 is received in compensation for heat radiated into space. 



2. Earthquakes due to steam explosions are apparently 

 very often the result of the opening of a fissure admitting 

 water to reservoirs of hot magma. The frequent earth- 

 quakes in Japan of this nature 1 are due to faulting in the 

 great geosyncline to the east of Japan. Sometimes, no 

 doubt, water accumulates by capillary infiltration for years, 

 and is transformed to steam by hot magmas. The steam 

 under pressure filling a cavity in the earth would be most 

 likely to explode during the passing of a great cyclone at 

 the earth's surface. The gravitational influence of the sun 

 and moon could also play the part of a liberating force 

 enabling the imprisoned vapours to burst through. Meteor- 

 ological and gravitational forces must have greatest 

 influence where large masses of steam and gas are con- 

 tained in subterranean reservoirs. As " Mathematicus" 

 writes in the "English Mechanic" 2 : — "No solar or lunar 

 influence, lasting only some hours, can move the magma to 

 rise thirty or forty miles in a narrow channel, whose friction 

 alone would keep the thick, adhesive, fluid back. But 

 gases acting during many years, heated to thousands of 

 degrees, and cooped up between the clumps of magma, 



1 See " Earthquakes " by J. Milne, pp. 228 and 281. 



2 " English Mechanic and World of Science/' No. 1951, Aug. 15, 1902. 



