O'Eeilly — On the Dates of Volcanic Eruptions. 413 



la violence de la gelee detruisirent une grande partie des vignes" 

 (Hermann) (Arago, "CEuv. comp.," yoI. 5, p. 206). The interval bet ween 

 the second eruption of 1157 and the first recorded, 1104, is 53 years, 

 which compares well with the known interval -1889-6 and + 1837-2 

 = 52-4, and would point to the year in question having been a year of 

 maximum. Towards this interpretation would also point the interval 

 between + 1615-5 and 1104 = 511-5, which agrees fairly well with 

 the normal interval 11*1 x 46 = 510-6. There is no entry as regards 

 the nature of the weather of this year in the records already referred 

 to. The year 1104 might therefore be considered as a maximum sun- 

 spot year from the foregoing data. 



The preceding observations in detail on the eruptions of Hecla may 

 be summarized as follows: — 











Estimated 





Erup- 



Date. 





Inter- 



sun-spot 



Differ- 



tion. 







vals. 



years. 



ences. 



1 



1104 



= 1104 



53 



-f 1104 ?? 



— 



2 



1157 



= 1157 



+ 1157 ?P 













48-93 







3 



1206, December 4, 



= 1205-93 



16-07 



+ 1206 ?? 



— 



4 



1222 



= 1222 



72 



- 1222 ?? 



— 



5 



1294 



==1294 



5-53 



+ 1294 ?? 



— 



6 



1300, July 10, .. 



= 1299-53 



40-95 



-f 1300 ?? 



— 



7 



1341, May 19, . . 



= 1340-48 



48-52 



-f 1341 ?? 



— 



8 



1389-90 



= 1389-90 



47- 



- 1389 ? 



— 



9 



1436 



= 1436 



73-57 



-f 1436 ?? 



— 



10 



1510, July 25, .. 



= 1509-57 



43-84 



-1510 ? 



— 



11 



1554, end of May, 



= 1553-41 



24-59 



-1552 ?? 



— 



12 



1578 



= 1578 



18-01 



- 1578 ? ? 



— 



13 



1597, Jan. 3 till March 



= 1596-01 



22-57 



- 1596, 01 ? 

 Wolf's List. 



— 



14 



1619, end of July, 



= 1618-58 



16-86 



- 1619 



0-58 



15 



1636, May 8, . . 



= 1635-44 



66-68 



- 1634 



1-44 



16 



1693, February 13, 



= 1692-12 



73-14 



-f 1693 



0-88 



17 



1766, AprU5, .. 



= 1765-26 





- 1766, 5 



1-24 



