•i94 Proceedings of the Royal Irish Academy. 



volcanic explosions. The periodicity of eruptions may tlius depend 

 upon the length, of time required for the storing up of sufficient steam 

 and on the amount of resistance in the crust to be overcome. In some 

 volcanoes the intervals of activity, like those of many geysers, return 

 with considerable regularity. In other cases the shattering of the 

 crust, or the npvrelling of vast masses of lava, or the closing of sub- 

 terranean passages for the descending water, or other causes, may 

 vary the conditions so much from time to time that the eruptions 

 follow each other at very unequal periods and with very discrepant 

 energy." 



If by the term " periodicity " may be understood that a definite or 

 determinable interval of time elapses between successive eruj)tions of 

 a given volcano, perhaps it would be better to limit the word to that 

 signification, and to use for the regular alternations in the eruption, 

 such as those referred to by Geikie in the cases of Stromboli, Yulcano, 

 (p. 198), &c.,the word "throb." 



It is in the first mentioned sense that Kluge uses the word 

 "periodicity," and in that sense alone will it be used in the present 

 paper. 



Geikie refers, on the note on p. 193 of his text-book, to Kluge's 

 article in the " Neues Jahrbuch " of 1862 "On the Periodicity of 

 Volcanic Eruptions." ]S"ow this article'^ has for its object to summarize 

 some of the conclusions arrived at by Kluge, in a much more ex- 

 tended work, not then published, and it tends mainly to show a 

 relation between the seasons of the year and the eruptions of volcanoes 

 situated in certain latitudes, and does not refer to the sun-spot period 

 at all. In this respect it may be useful to give an outline of the 

 article.^ 



He states that he has been engaged for a length of time on an 

 important work on the periodicity of volcanic eruptions and com- 

 municates some of the results. The total number of eruptions included 

 in his catalogue, and of which the years of occurrence, at least, are 

 sufficiently determined, amounts to 1297, which relates to 348 different 

 " localities," since the term volcano can hardly be strictly applied in 

 this case. " Ey far the greater number of these eruptions belong to 

 the eighteenth and ninteenth centuries, since up to the year 1700 

 I could only find 368 mentioned." He explains the difficulty of 



1 "Ueber die Peiiodicitat vulkaiiischer Ausbriiche," von Herm Dr. Emil Kluge 

 in Chemnitz. Aus einem Brinfe an Professor Bronn. — Xeue& Jahrbuch, 1862, 

 p. 582. 



