SUNSPOT MINIMA AND VOLCANIC ERUPTIONS. 47 



1887, all, except 1852 perhaps, minimum years. Those of 

 Java were most severe in 1822, 1833, 1843, 1852, 1874- 

 1878, 1 1883. Those of Hekla were most noticeable in the 

 minimum years 1783, 1843, 1875 ; tliose of La Soufriere in 

 the years 1812 and 1902, and of Mount Redoubt in 1867 

 and 1902. The eruptions of Vesuvius are apparently also 

 as a rule contemporaneous with a particularly fine corona, 

 such as usually occurs in minimum years. 



Milne mentions that at Oopiapo the people expect a great 

 earthquake once in every twenty years, at Lima every 

 hundredth year, great devastating earthquakes having 

 occurred in 1578, 1678, 1778, 1878, two of these actually 

 taking place at the same hour on the same day. 



The reason why all outbursts do not occur at sunspot 

 minima is plainly that other causes are also at work in 

 locating the time and place of volcanic outbreaks in addition 

 to the chief agent above mentioned. There are perhaps 

 some purely terrestrial causes, such as chemical action ; 

 the moon's influence is not to be ignored, and there is also 

 planetary attraction. One great immediate cause of an 

 earthquake may be the sudden relief of atmospheric pres- 

 sure by the passage of a vast cyclone over an area. A 

 sudden increase of pressure might start a volcanic eruption. 

 However, in connection with these matters it will be as 

 well to quote the views of some well known authorities. 



Mallet observed that in European regions seismic minima 

 seemed to coincide with barometric minima. 



M. Alexis Perrey investigating the moon's influence found 

 that out of 5,388 earthquakes studied by him, 2,761 or 51°/°, 

 occurred at syzygies, and 49°/° at quadratures. Lapparent 

 in his Geologie, whilst admitting the correctness of M. 

 Perrey's research, considers the difference too trifling to 

 found a law upon. 



1 The eruptions of Le Kaba in Java, 



