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XXIY. 



0^^ THE DATES OE YOLCA^'IC EEUPTIOXS AND THEIR 

 CONCOEDAIs^CE WITH THE SUIs"-SPOT PEEIOD. By 

 JOSEPH P. O'REILLY, C.E. 



[Eead Apkil 24th, 1899.] 



VoLCA2s^ic eruptions and the phenomena connected therewith, have at 

 aU times excited the interest of mankind, and have received and con- 

 tinue to receive, on the part of scientific observers, the very closest 

 attention, not only on account of the magnitude of the phenomena 

 involved therein and their great geological significance, but also by 

 reason of the destruction of life and property -with Tvhich they are 

 not unfrequently accompanied. 



Hence in all works on geology this subject is generally very fully 

 treated in all its essential aspects. One particular however, the 

 question of their periodicity, seems either to be avoided or to be 

 treated as not offei-ing sufficiently precise data, to allow of its 

 receiving recognition, reference however being made to the authors 

 who have mainly occupied themselves with this particular branch 

 of the subject. 



Reference to the question is made in " Geikie's Text-book of 

 Geology," 1885, p. 193, as follows :— 



"Kluge has sought to trace a connexion between the years of 

 maximum and minimum of sun-spots, and those of greatest and 

 feeblest activity (of volcanoes), and has constructed lists to show that 

 years which have been specially characterised by terrestrial eruptions 

 have coincided with those marked by few sun-spots and diminished 

 magnetic disturbance."^ 



" Such a connexion cannot be regarded as having yet been satis- 

 factorily established. Again, the same author has called attention to 

 the frequency and vigour of volcanic explosions at or near the time of 

 the August meteoric showers. But in this case, likewise, the cited 



^ " TJeber Synclironisinus and Antagonismus, 8vo., Leipzig, 1863, p. 72. A. Poey 

 (Compt. Eend. Ixxviii., 1874, p. 51) believes that amoug the 786 eruptions 

 recorded by Kluge betxreen 1749 and 1861, the maxima correspond to periods of 

 minima in solar spots. See, ho^^eYer, postea, pp. 250 and 259." 



