SUNSPOTS AND VOLCANIC AND SEISMIC PHENOMENA. 53 



(6) The theory that enormous quantities of water And aceess 

 to hot magmas through gradual infiltration by capil- 

 larity, as well as occasionally by way of fissures. 1 



For the purpose of this paper I propose to discriminate 

 between (1) eruptions of a violently explosive character, 

 and (2) those of a gentler nature, usually accompanied by 

 lava flows. The latter kind seem to depend, essentially, 

 on the same causes as earthquakes, and predominate at 

 sunspot minima ; they are usually preceded by the opening 

 of a fissure which allows deep seated magmas an upward 

 passage. The eruptions of the former kind are commonest 

 in very unstable and much faulted areas, and in regions 

 undergoing heating from rise of isogeotherms, especially 

 where the volcano is situated in an artesian or subartesian 

 basin. Here water would be continually finding its way 

 down to the volcanic foci, and perhaps more in wet than 

 in dry years. 



Vesuvius, situated in a basin of porous sedimentary rocks, 

 seems to bear out this supposition. In its eruption of 1872, a 

 very wet year (close to a sunspot maximum), its lava was very 

 liquid, and on cooling became extremely cindery and scoriaceous 

 from its volumes of enclosed steam. While previous lava flows 

 offer no impediment to the pedestrian, the flow of 1872 is practi- 

 cally impassable (See Judd's "Volcanoes," pp. 98 and 99, Internat. 

 Scientific Series). It is interesting to note that the year 1872 

 was exceedingly wet and stormy throughout Europe ; this was the 

 year of the great Baltic storm. A violent north-west wind was 

 blowing at the time of the Vesuvian eruption of April, 1872. The 

 peculiar meteorological conditions prevalent at the time may have 

 played some part in bringing about ths eruption. (See "Volcanoes," 

 pp. 24-29.) 



1 This theory of earthquake and volcanic action is supported by the 

 fact that most of the earthquakes of Japan originate beneath the sea, 

 where infiltration must be greatest ; and the violent explosions accom- 

 panying many volcanic eruptions are undoubtedly due to steam. 



