O'Reilly — On the Bates of Volcanic Eruptions. 409 



It may be remarked at once, that the eruptions which occurred 

 during the summer months predominate, as indicated by Kluge. 

 As regards the connexion with sun-spot period years of maxima or 

 minima, the four last mentioned can alone be discussed, strictly 

 speaking, since Wolf's list only goes back to 1610-8. For these, 

 however, the correspondence is fairly good. 



No. 14, 1619 (July, end of) = 1618-58, Wolf s list, 1619 minimum. 



No. 15, 1636 (May 8th) = 1635-35, ,, 1634 minimum. 



No. 16, 1693(Feb. 13th to Aug.) = 1692-12— 1692-67, Wolf's List, 



1693 maximum. 

 No. 17, 1766 (5th April) = 1765-25, Wolfs List, 1766-5 ± 05 



minimum. 



As regards the dates prior to 1610, all that can be attempted is to 

 estimate according to the intervals occurring between them, and any 

 of the known years of Wolf's list, and examine how far these 

 intervals correspond. Taking thus the eruption of 1597, we may ask 

 if this year was, in all probability, a minimum or a maximum year of 

 the sun-spot period. Now the period being in the mean 11-11 (or ll'l 

 years as more usually taken), the interval between 1619 and 1597 is 

 just 22 years, that is, twice the period ; and it may be assumed that 

 the 13th eruption mentioned in the list as occurring January 3rd, 

 till March 1597 (= 1596-08 to 1596-25), corresponds to a minimum of 

 sun-spots. 



The interval between the twelfth and the thirteenth eruption, 

 that is, between 1597 and 1578 is 19 years, which may or may not 

 represent a double interval between maxima or minima years — in 

 this case ; or may represent an interval of years between a maximum and 

 a minimum, or vice versa. Thus we have the interval between- 1889-6 

 -f 1870-7 - 18-9 years. We have also the interval between- 1619 

 and 1578 = 41, which compares well with the interval between 



- 1889-6 and + 1848-6 = 41 years, as also the interval between 



- 1645 and 1578 = 67 years, which compares fairly with the interval 



- 1889-6 and - 1823-2 = 66-4 years. Lastly, I may cite the interval 

 -^655 and 1578 = 77 years, which is practically a multiple of the sun- 

 spot period, and would make this twelfth eruption correspond to a 

 presumed minimum year, but it may possibly have corresponded with 

 a maximum year. 



There is a further circumstance to be noted in this respect, and 

 which may have some value in deciding whether this eruption 

 corresponded to a minimum or to a maximum ; it is the character of the 



E.I. A. PEOC., SEE. III., VOL. V. 2 G 



