ON THE SECULAR PERIODICITY 



103 



actions of London make no mention of auroras before 17 1C, though they had been 



published for forty years ; but they record two hundred observations, made in different 

 places, between 1716 and 1750* The Academy of Sciences, founded at Paris in 1G06, 

 is silent upon the subject for fifty years after its establishment. 



E. J. Burman writes under the date of October 30, 1722, that the aurora hud been 



Upsal thirty times during the last five months 



Celsius states it had been 



rarely seen in Sweden before 1716, and yet between 1716 and 1732 there maybe 

 found three hundred and sixteen observations on two hundred and twenly-foui inde- 

 pendent recurrences of the phenomenon. He heard from the old men then living at 

 Upsal, that these northern lights were novel even to them in that high latitude, and he 

 concludes, from all the evidence he could collect, that these phenomena were periodical 



the arctic circle as well as on the parallels of Europ 



It is impossible to believe 



says Celsius, " that the skilful observers of the last century, who patted their lives 

 the Observatories erected for them, particularly at Paris and Greenwich, should 



have taken care to transmit to posterity their observ 



on this admirable phe 



nomenon, if it had appeared in th 



time." Mairan adduces also the authority of 



Anderson, found in his Natural History of Iceland. « It has always appeared extraor- 

 dinary to me," he says, u that the most ancient Icelanders, as they have assured me 

 should have been astonished themselves at the frequent appearance of the aurora in 

 their island, declaring that formerly they were much less common than to-day 

 " But I am so much the 



mor 



eady to believe them 



ther 



of Europe this phenomenon was much more uncommon formerly than 



The first recorded appearance of an aurora in Italy belongs to the year 1 727.t Zanotti 



tions of it in Bologna and other parts of 



exhib 



Zanott i 



and Beccari have collected fifty-two 



Italy, between the years 1727 and 1751, and thirty-six doubtful cases 



description of the aurora which was seen in Italy, as well as in England, on December 



16, 1737, says : "The Aurora Borealis, which was formerly a rare phenomenon, and 



almost unknown in this our climate (Italy), is now become very frequent. A great 



number have been observed for some years past." % The language of Halley, Leib 



Kirch, Fontenelle, and Miraldi, in describing the 



of the first half of the 



eighteenth century as uncommon sights, and the silence of Cassini in respect to any such 

 display in the latter half of the preceding century, point to one and the same explana- 



tion. 



The periodicity in the occurrence of the 



* Bertholon in Encyc. Method. 

 X Phil. Trans., XLI. 593. 



which seems to be roughly fore 



f Musscbenbroek, Nat. Phil., 1314 





