412 Proceedings of the Royal Irish Academy. 



It may thus reasonably be assumed that 1341 was a sun-spot year 

 and probably a mfl!;rmMm. Between the seventh and the sixth eruptions 

 (1341 and 1300) the interval is 41 years. This compares well with the 

 known interval between - 1889'6 and + 1848-6 = 41 years; and this 

 coincidence points to the year having been probably a maximum sun-spot 

 year. As regards the weather of this year, there is no mention made 

 in our. annals or in Arago's work. Between the sixth and the fifth 

 eruptions (1300 and 1294) the interval is 6 years, that is about the 

 usual number of years which occur between a maximum and a minimum. 

 Thus taking the interval between + 1615-5 and 1294, we get 321-5 

 years, which agrees well with the normal interval represented by 

 11-1 X 29 = 321-9. It may therefore be assumed that 1294 was a 

 maximum sun-spot year. There is no mention in the records as to the 

 character of the weather of this year. 



Between the fifth eruption and the fourth (1294 and 1222), the 

 interval is 72 years. This again would point to an interval such as 

 66-6 + 5-4, that is, a normal interval 66-6, and the usual period 

 from maximum to minimum. Thus we have the known interval -1 889-6 



- (+ 1816-1) = 73-5. On the other hand, we have the interval 



- 1610-8 - 1222 = 388-8, which compares well with the normal 

 interval, ll'l x 35 = 388-5. It would therefore be allowable to con- 

 sider this year as a sun-spot year either of maximum or of minimum. 

 Prom the fact of there being no mention in the records as to the 

 nature of the weather during this year, it might probably have been a 

 minimum year. 



The interval between the fourth and the third eruption (1222-1 206) 

 is 16 years, which maybe interpreted as (11-1 + 4-9), that is an inter- 

 val from one minimum to another, plus the time to the next maximum. 

 Thus, if we compare this year with + 1615-5, the difference (+ 1615-5 



- 1206) comes out 409-5, which compares well with the normal inter- 

 val IM X 37 = 410-7. 



The records of the Annals of Ulster for the year 1205 are interest- 

 ing in this respect: — "A great frost and snow from the calends of 

 January to Patrickmass this year." The year 1206 may therefore be 

 assumed to be a sun-spot year. 



The year 1157, second eruption, gives with the year 1206, third 

 eruption, an interval of 49 years (the same as between the seventh and 

 eighth eruptions). Compared with -1610-8, it gives the interval 



- 1610-8 - 1157 = 453-8 years, which approximates fairly to the normal 

 interval ll'l x 41 = 455-1 years. The entry as regards the weather of 

 the year in Arago's work is as follows : — " L'immensite de la neige et 



