416 



Proceedings of the Royal Irish Academy. 



ll'l X 27 = 299-7. For these reasons the year in' question maybe 

 taken as a minimum sun-spot year. 



The interval between the fourth and the third eruption (1310-07 

 and 1262) is 48-07, which exceeds the normal interval 44-4 by 3-67, 

 and which may, therefore, represent the interval between a minimum 

 and a maximum. Moreover the interval between + 1615-5 and 1262 is 

 353-5, which differs little from the normal interval, 355-2 (=11-1 x 32), 

 the difference being only 1-7. This year 1262 may, therefore, be 

 taken as a maximum year of sunspots. The record for the weather of 

 this year is thus given in the " Annals of Ulster " : — " There was a 

 great drought this year, and a very hot summer." (-'Annals of 

 Clonmacnoise.") 



The interval between the third and the second eruption is 17 years, 

 which is not very different from that between - 1889-6 and + 1870*7 = 

 18-9. That is, it may be read as the difference between a maximum and 

 a fuinimum year, or vice versa. Kow if the interval between the sun- 

 spot year, - 1610-8 and 1245, be taken, we get 365-8,which agrees 

 fairly well with the normal interval 366-3 (=11-1 x 33), so that this 

 year may be taken as a minimum sun-spot year. 



The eruptions of TroUadyngia mentioned in Boehmor's Paper are 

 only six in number, and are as follows with the intervals and the 

 estimations as regards their relations with sunspot years : — 



Erup- 





Inter- 



Sunspot 



tions. 



Date. 



vals. 



years. 



1 



1151 



37 



+ 1150? 



2 



1188 



152 



-1188? 



3 



1340 



20 



+ 1341? 



4 



1360 



29 



+ 1360? 



5 



1389-90 



21 



-1389? 



6 



1510 





-1610? 



The fifth and the sixth eruption dates have already been considered 

 along with the Hecla dates, and must of course be taken as being 

 minima sun-spot years, as in the case of Hecla. 



The interval between the fifth eruption and the fourth (1389 and 



