400 Proceedings of the Royal Irish Academy. 



mentioned, a practicable ground for the recurrence of a 100 years' 

 period as regards tlie last-mentioned. Prom the numerous examples 

 of this recurrence, which may be here stated, I may be allowed to cite 

 the following." Here he cites amongst other cases : — 



Etna, . . 1183, 1285, 1381, 1682, 1781, &c. 



Yesuvius, . . 685, 983, 1184, 1682, 1783, 1784, 1785 ; 203, 

 1306, 1506, 1704, 1705, 1706, 1804, 1806 ; 



51, 1712, 1713, 1813 ; 



1660, 1760, 1860— 



in all about 200 different dates arranged in groups, as in the cases 

 here cited. 



[Page 14.] "Although chance may often TTonderfuUy intervene, 

 and may be often helped out by clever combinations of data, neverthe- 

 less it seems to me that in most of the above-mentioned cases, there 

 is something more than a mere casual coincidence, something, in fact, 

 regular in its nature since the phenomena arise so very frequently in 

 the case of volcanoes which do not present many cases of eruption. 

 It cannot almie depend on a periodic return of years 2Joor in sunspots, 

 since even years such as 1837, and rich in sunspots, follow one another 

 at intervals of many hundred years. In examining the connection 

 between volcanic eruptions and earthquakes I propose to revert to the 

 subject." 



He then enters on the detailed examination of different volcanic 

 districts as regards the examples furnished by them of synchronisms 

 and antagonisms. 



" As regards Italian districts, it may be generally admitted that 

 the activities of the two volcanoes, Yesuvius and Etna, alternate, as 

 already shown by Y.Hoff (' GeschichtedernaturlischenYeranderungen 

 der Erdoberflache,' Y. Hoff, 2 Th. p. 262). A glance at the cuiwes 

 shows this better than the citation of the individual outbreaks." 



[Page 16.] Although the alternating activity of the two volcanoes 

 may be accepted as a rule, there occur, however, periods during which 

 both were simultaneously in activity {e.g. 1822-1643). 



[Page 19.] A somewhat similar relation of alternating activity as 

 shown by Yesuvius and Etna manifests itself in the case of the Italian 

 volcanoes when compared with the Greek ones. 



"Hardly in any country (with the exception of Chili more par- 

 ticularly) is it so convincingly demonstrated by simultaneous eruptions 

 of far distant volcanoes, that these eruptions have their origin in a 

 common source, and that the volcanoes are but openings or vents on 



