SUNSPOT MINIMA AND VOLCANIC ERUPTIONS. 53 



(1) The most likely theory seems to be that at sunspot 

 minimum, when less energy is received from the sun, the 

 earth cools quicker and radiates more heat and perhaps 

 magnetism into space. The radiation of heat would be 

 further favoured by the absence in the atmosphere of the 

 usual protective canopy of moisture. When this rapid 

 cooling is progressing, there will obviously be more con- 

 traction, hence cracking, in the earth's crust, and conse- 

 quently more earthquake shocks. 



The strongest objection to this theory is the fact that 

 the passage of heat through rock is a slow process, and 

 that electrical radiations are also supposed to be checked 

 by passing through a layer of rock. But if we give credence 

 to statements lately made, that the Marconi electrical 

 waves can pass directly through a mountain, the difficulty 

 is lessened. For then it would appear that some of the 

 solar rays might have the power to pass through the solid 

 rock, and that the earth would be able to send out similar 

 radiations. These radiations in making their escape might 

 be partly transformed into heat at points where resistance 

 is offered, as at the fissures in the earth's crust. From 

 accounts of great earthquakes and eruptions it certainly 

 seems that there is a great evolution of electricity or 

 magnetism as well as heat, accompanying the phenomena. 



(2) Another possible explanation of this connection 

 between solar physics and seismic phenomena, is that the 

 atmosphere by contraction and increasing its pressure at 

 the earth's crust, exerts a squeeze on the earth's crust. 

 This makes itself most felt at the lines of weakness, where 

 lavas are consequently squeezed out through volcanic vents, 

 or up into zones of no strain thus causing earthquakes. 



(3) Alterations in magnetic conditions may have some- 

 thing to do with causing earthquakes. A friend of mine 

 who was serving on board an American man-of-war in 1868, 



