30 Scientific Proceedings, Royal Dublin Society. 



a.d. 628 and a.d. 886, have divided it into 26 periods of 10 years, 

 between which the following intervals occur : — 



40 years between the 2nd and 6th, 

 60 „ „ 6th „ 12th, 



40 „ „ 12th „ 16th, 



40 „ „ 16th „ 20th, 



40 „ „ 20th „ 23rd; 



and from "the author's explanatory notes a still more correct 

 table can be deduced, by means of which the cycle of earthquake 

 intensity is finally put at 33*3 years, or 3 x 11*1, that about 

 three times the sun-spot cycle (Lockyer gives 10 years; Flammarion 



11*). 



A further deduction is made, that earthquakes of a disastrous 



nature occur once every 59 years, so that the next great catastrophe 

 may be expected in 1913. 



Now it will be remarked that the interval of 200 years of rest 

 mentioned for Krakatoa so far corresponds to a multiple of the 

 short period of 10 years, adopted as interval of groups, represent- 

 ing also the period of sun-spots. 



Admitting that the earth were once in a state somewhat as is now 

 the sun, may it not have had in a similar manner a recurrence of 

 phenomena such as the sun-spots, and may not this recurrence be 

 still observable in the existence of a period or cycle in volcanic and 

 earthquake action ? When working at the Catalogue of European 

 earthquakes which I submitted to the Royal Irish Academy last 

 April, I noted a recurrence of a period or interval of 10 years in 

 many cases, but so exceptionally that I could not point to it as 

 a law ; however, a further examination of the data existing may 

 be more conclusive in this respect. 



