428 Proceedings of the Royal Irish Academy. 



1630-97 and 1500 is 130-97, wtich approaches sufficiently the normal 

 interval 133-3, to allow of its being taken as an usual interval, since, 

 as a matter of fact, we have the interval -1889-6 -(+1761-5) =128-1, 

 differing from the normal interval still more. The weather for this 

 year is thus mentioned in the " Annals of Ulster" : '* This year (1500), 

 from the middle of September till the end of winter, Ireland endured 

 rains and many tempests." (Ware's " Annals.") " Great inclemency 

 this year which killed almost all the cattle of Erin, and prevented the 

 earth responding to the husbandman." This year may, therefore, be 

 taken as a minimum sun-spot year. 



The interval between 1500 and 1306 is 194 years, which compares 

 well with the interval occurring between the known sun-spot years 

 -1889-6 and (+) 1693 = 196-6. Moreover, the interval between the 

 year + 1615-5 and 1306 = 309-5, which differs only by a unit from the 

 normal interval 310-8 (=11-1 x 28). The weather of this year is thus 

 mentioned in Arago's work already cited, p. 268 : " La gelee fat tres 

 forte en France dans cet hiver " (Papon, ''Hist, du Province," t. iii.) : 

 " La mer fut prise sur les cotes de Flandre et de I'Hollande sur une 

 largeur de 3 lieues (I'Abbe Maim, "Mem. sur les Grandes Gelees, 

 1792"). 



The date 1305-5 has been estimated as the maximum sun-spot year 

 corresponding to this eruption. 



The year 1138-9 makes with the previous one 1306, an interval 

 of 168 years, which differs so little from the normal interval 166-6, 

 that it may be accepted as normal. 



Furthermore, the interval between the maximum year + 1615-5 

 and 1138 is 477-5, which practically agrees with the normal interval 

 477-3 (=11-1 X 43). There is no mention in the records of the 

 weather of this year, which has been taken as a maximum sun-spot 

 year. 



Between the year 1138-9 and 1049 the interval is 89 years, which 

 represents closely the normal interval 88-8 (=11*1 x 8). Moreover, 

 the interval between the sun-spot years +1615-5 and 1049 is 566-5, 

 which practically agrees with the normal interval 566-1 (=11-1 x 51). 

 For those two reasons the year is taken as a m.aximum sun-spot year. 

 There is no mention of the weather of the year in the records already 

 referred to. 



Between the years 1049 and 1036j^the interval is 13 years, 

 which approximates to the normal interval 1 1 • 1 , while on the other 

 hand the interval between the sun-spot year + 1615-5 and 1036 = 579-5, 

 which only differs from the normal interval 577-2 (= ITl x 52) by 2-3. 



