O'Reilly — On the Dates of Volcanic Eruptions. 411 



est cite comme rigoureux dans les receuils hollandais. En Italie le 

 froid fut tres intense ; la neige tomba abondamment et la gelee fut 

 assez forte pourqu'au siege de Mirandole les soldats du pape 

 Jules II. pussent traverser les fosses sur la glace (Guicbardin, 

 Hist, d'ltalie)." 



The year 1510 may therefore be taken as a minimum year of sun- 

 spots, more particularly for the first-mentioned reasons. 



The ninth eruption, that of 1436, shows an interval from the tenth 

 of 74 years, which differs from the normal interval of 77"7 years by 

 3-7. However, we have actually the interval of 73-5 years between 

 — 1889'6 and+ 1816*1, so that the year 1436 may have been a maximum 

 year of the sun-spot period. As regards the winter of that year, the 

 Annals of Ulster give the following entry for 1435 (1435-6) : — "An 

 unusual frost and ice occurred in this year, so that the people used to 

 traverse the rivers and lakes of Ireland on the solid ice." 



Arago's list says, p. 270: L'hiver de cette annee (1435) fut re- 

 marquable par la duree and la rigueur du froid. II dura en Flandre 

 depuis le commencement de Decembre jusqu'au mois de mars et I'epais- 

 seur de la glace fut de plus d'une aune (Annales Me^ere). En AUe- 

 magne beaucoup de personnes moururent de froid (Chronicon Ele- 

 vasense).'^ 



It would be reasonable to presume that the year 1436 was a 

 sun-spot year, either of maximum or minimum, or at no great interval 

 from one. 



Between the ninth eruption of 1436 and the eighth of 1389-90, the 

 interval is 46 years, which exceeds the normal interval of 44*4 by 

 1"6 year, a sufiiciently close approximation to allow of this year 

 1389-90 being considered as a minimum of sun-spots. If it be compared 

 with the minimum year 161 0*8 of Wolf's list, the interval comes out 

 221-8 years (222-221-8 = 0-2), which only differs from the normal 

 interval by 0-2 year. 'Eo mention occurs in Arago's work as regards 

 the weather of this year, nor in our annals. 



Between the eighth and seventh eruptions, 1389-90 and 1341, the 

 interval is 49 years ; this may be interpreted as the difference between a 

 minimum year and a maximum. That this may be so, is proved by the 

 interval which occurs between - 1889-6 and + 1615-5 = 274-1, while 

 between -I- 1615-5 and 1340-46, the interval is 275-04. Asregardsthe 

 weather of this year, Arago's list mentions, under the date 1341, 

 p. 269 : " Le Eroid de cet hiver fut si rude en Livonie que beaucoup 

 de soldats de I'armee des croises eurent le nez, les doigts ou les 

 membres geles." 



