O'Reilly — On the Dates of Volcanic Eruptmis. 429 



If the date 1035-5 be taken as a sun-siDot maximum year, the agreement 

 becomes practically sufficient. 



Between 1036 and 993 the interval is 43, which is so very close to 

 the normal interval 44*4 as to allow of its being estimated as a sun- 

 spot maximum year. Moreover the interval between the maximum 

 year + 1615'o and 993 = 622*5, which differs only by a unit from the 

 normal interval, 11 "1 x 56 (= 621-6). As regards the weather of this 

 year there appears the following record in Arago's work already cited, 

 p. 263 :— 



993. — "Depuis le St. Jean (24 Juin) jusqu'au 9 ISTovre. c. k d. 

 pendent presque tout I'ete et I'automne il fit une secheresse et une 

 chaleur excessives." 



994. — " L'hiver fut tres rude en Allemagne et la grele dura presque 

 sans interruption depuis le 12 ISTov. jusqu'au milieu de Mai, le 

 printemps et I'ete amenerent des fleaux de toute sorte." 



The interval between 993 and 685 is 308 years, which differs 

 from the normal interval 310-8 - (11*1 x 28) by 2*8 an approximation 

 practically sufficient. On the other hand, the interval between the 

 sun-spot maximum year + 1615*5 and 685 is 930-5, which again differs 

 from the normal interval, 932-4 (= iri x 84) by 1-9, so that the year 

 in question may be taken as that of a sun-spot maximum. The following 

 record of the weather for 684 occurs in the " Annals of the Four 

 Masters " : " There was great frost in this year, so that the lakes and 

 rivers of Ireland were frozen, and the sea between Ireland and 

 Scotland was frozen, so that there was a communication between 

 them on the ice." 



The interval between 685 and 512 is 173, which compares fairly 

 with the interval -1889-6 and + 1718-2 =171-4, the difference being 

 1*6, On the other hand the interval between this year and the 

 minimum sun-spot year -1610-8 is 1098-8, which practically agrees with 

 the normal interval is 1098-9 (= ll'l x 99), so that this year may be 

 taken as a minimum sun-spot year, or more exactly 511, which would 

 give a complete concordance. 



Between 512 and 472 the interval is 40, which differs from the 

 normal interval 44.4, but which approximates to the actual interval 

 - 1889-6 and + 1848-6 = 41 years. If the interval be taken between 

 the maximum sun-spot year + 1615-5 and this year, we get 1143-5, 

 which very closely agrees with the normal interval 11-1 x 103 

 (= 1143-3), so that this date may be taken as representing a maximum 

 sun-spot year. There is no weather record for this year in the works 

 already referred to. 



