398 Proceedings of the Royal Irish Academy. 



between the occurrences of earthquakes in countries widely distant 

 the one from the other, so has attention been directed to the simulta- 

 neity or alternation of volcanic eruptions, only generally so far as 

 conclusions might be drawn therefrom, as to the subterranean con- 

 nection or common focus of energy of all volcanoes. 



He shows the necessity of defining what may be understood as 

 ^^Synchronism'''' in this respect, and examines the different cases 

 that may be brought under this head, as also those representing 

 ^^ A?itayonism" or alternation of action between volcanoes or volcanic 

 groups. Examining the different cases stated from the point of view 

 of their scientific interest he considers more particularly two specific 

 cases : — 



(a) Two or more volcanoes enter into eruption simultaneously, 

 and as it were at the same moment, so that it would appear as if the 

 outbursts were the effect of a common cause, acting, however, at 

 different points of the earth's surface. 



(h) A volcano ceases its activity at the very moment that another 

 enters on a state of activity. 



These he considers as typical cases, since they admit of the least 

 amount of illusion, or of play of accident, as to the presumed common 

 cause. 



On page 3 he says: — " It may, furthermore, be of imjDortance to 

 examine whether certain spaces of time be, or be not, signalised by 

 numerous simultaneous eruptions, and whether these spaces of time 

 return after some determinate period. 



"In the following pages I have sought to bring some of these 

 questions to a decisive answer. The material in hand is, however, 

 not yet sufficiently abundant to allow of more than an approximate 

 determination, meanwhile the results already attained maybe of some 

 importance, even should they have no further significance than in 

 proving as untenable certain received theories, or in leading the way 

 to further research. 



"Before entering upon the investigation of distinct volcanic 

 countries, the following question may be at once answered. Do 

 certain years distinguish themselves markedly by the great number 

 of their eruptions ? A mere glance at the curves given herewith is 

 sufficient to prove that they suddenly and frequently rise, as for the 

 years 1793, 1822, 1835, 1843, 1852, and almost as suddenly fall." 



He then enters on a detailed account of the volcanic and seismic 

 events of the year 1822, including some belonging to 1821, to show 

 their frequency and importance during the period considered. 



