SUNSPOTS AND VOLCANIC AND SEISMIC PHENOMENA. 45 



causes quite insufficient singly to cause seismic disturb- 

 ances. Still several of these secondary causes co-operating 

 might perhaps cause an earthquake, or one of them alone 

 might, in a somewhat unstable region, precipitate seismic 

 disturbances. Temperature changes indirectly also play a 

 small part in seismology. It has been noticed that in 

 temperate and arctic regions more earthquakes occur in 

 winter than in summer. This may be due in some parts to 

 secular cooling proceeding more rapidly, in other parts to 

 the heavy loading of the earth with ice and snow. 



In my paper, read before this Society on June 4th, 1902, 

 I gave an account of work done by various physicists, 

 meteorologists and astronomers on the subject of sunspots 

 and their meteorological and magnetic effects. I advanced 

 in my paper that sunspots likewise bear a relation to seismic 

 and volcanic disturbances. At the same time Sir Norman 

 Lockyer advocated similar views in England. In a letter 

 to the Times, May 19th, 1902, Sir Norman Lockyer writes 

 that earthquakes and eruptions are most frequent at sun- 

 spot minima and maxima. My view was, and is, that these 

 phenomena are at a maximum when sunspots are at a 

 minimum, although from my later researches it seems that 

 at sunspot maxima there sometimes is a violent and 

 spasmodic outburst of volcanic violence, I wish here to 

 investigate more fully than before the reasons of the inter- 

 dependency of these terrestrial and solar phenomena. 



The great objection to the sunspot theory of seismic and 

 volcanic disturbances is the fact that rocks conduct heat 

 at a very slow rate. Rocks are also impenetrable to elec- 

 trical waves, Hertzian waves, etc. The annual variations 

 of earth temperature at a depth of thirty feet are almost 

 nil. Hence, assuming that w r e receive more solar energy 

 during sunspot maxima it certainly cannot affect rocks at 

 some depth, if it has to pass thither in the form of heat, 



