O'Reilly — On the Dates of Volcanic Eruptions. 423 



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

 referred to. 



The interral between the year 1169, 4th February, 1168-9, and 

 the preceding is twelve years, which is sufficiently close to the normal 

 interval ll'l to allow of this year being considered as a minimum. 

 The year was remarkable on account of the violence of the eruption. 

 it is cited as having been " the most tremendous eruption of ancient times.''^ 

 It is therefore interesting to compare it, as interval, with the date of 

 the equally celebrated eruption of 1669, March 8th = 1668-18, the 

 difference is 500-09, the normal interval would be ll'l x 45 = 499-50, 

 so that the difference is less than a iinit, and as the nearest sun-spot 

 year to 1668-18 was a minimum, 1168-09 would be therefore a, minimum. 

 There is no reference in the works cited to the weather of that year. 



The interval between the year 812 and theprecediugyearis 356-09, 

 which is very near to a normal interval 11-1 x 32 = 355-2, differing 

 only by 0-89. If we take the interval between this year and the 

 minimum year- 1610-8, we get 798-8 years, which again is practically 

 equal to the normal interval, 11-1 x 72 = 799-2, so that the year in 

 question may be regarded as a minimum year. 



The year 420 makes with the preceding one an interval of 392, 

 which, not representing a complete normal interval, may be read 

 388-5 (= iri X 35) -1- 3-5, that is an interval between a mmm^^m and a 

 maximum. But it does not correspond sufficiently well with any of the 

 sun-spot years to allow of its being noted either as a maximum or a 

 minimum. 



The interval between the year 253 and the preceding year is 167, 

 which corresponds well with the normal interval 166-5 = 11-1 x 15. 

 Otherwise there is no indication as to its relation with the sun-spot 

 period. 



The interval between the year 72 and the preceding year is 181, 

 which does not represent a normal interval. If the interval be taken 

 with + 1615-5, an interval of 1543-5 is found, which differs slightly 

 from the normal one 11-1 x 139 = 1542-9, but is hardly sufficient of 

 itself to fix the character of the year. 



The interval between the year 40 and the last is 32 years, which 

 is sufficiently close to the normal interval 33-3 to allow of its being 

 considered as a sun-spot period year. 



The dates about this period, that is the first and second centuries 

 A. D., and the dates prior to these need not be further examined. A 

 single example, however, is worth consideration, that is b. c. 477. 

 If this figure be added to - 1610-8 we get 2087-8, which very closely 



