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THE POPULAR SCIENCE MONTHLY. 



oculation which have been followed out, and 

 others which are still incomplete. Of the 

 cases, twelve experienced between the fourth 

 and the twenty-sixth day of inoculation a 

 mild attack of yellow fever ; twenty-four ex- 

 perienced no symptoms within twenty-five 

 days, but contracted a mild attack before the 

 end of three years ; twelve exhibited no 

 symptoms of the disease within three years ; 

 three, who had no symptoms within twenty- 

 five days, contracted well-marked yellow 

 fever within three years ; and one, who had 

 a mild attack in consequence of inoculation, 

 contracted a severe attack later on which 

 proved fatal. Thus only eight per cent of 

 those who had been inoculated contracted 

 the disease in a well-marked form, and the 

 mortality was less than two per cent. Of 

 sixty-five monks who came to Havana and 

 lived there under similar conditions, thirty- 

 three were inoculated and thirty-two were 

 not. Only two of those who were inocu- 

 lated had well-marked attacks, and these 

 were not fatal ; while eleven of those who 

 had not been inoculated were severely at- 

 tacked, and five died. But inoculations peri- 

 formed in cold weather do not seem to be 

 wholly trustworthy and need to be repeated 

 in the spring ; also it appears that a person 

 who has been three years in the city without 

 having the disease has become acclimatized, 

 and is not likely to be attacked afterward. 



Facts abont the Aurora Borealis. The 



present condition of the investigation of the 

 phenomena of auroras is thus described by 

 Mr. G. S. Griffiths, F. G. S., F. R. S., in an ad- 

 dress on the objects of antarctic explora- 

 tion. The nature of auroras, the author 

 says, is very obscure ; but recently a distinct 

 advance has been made toward discovering 

 some of the laws which regulate them. 

 " Thanks to the labors of Dr. Sophus Trom- 

 holt, who has spent a year within the Arctic 

 Circle studying them, we now know that 

 their movements are not as eccentric as they 

 have hitherto appeared to be. He tells us 

 that the aurora borealis, with its crown of 

 many lights, encircles the pole obliquely, and 

 that it has its lower edge suspended above 

 the earth at a height of from fifty to one hun- 

 dred miles, the mean of eighteen trigonomet- 

 rical measurements, taken with a baseline 

 of fifty miles, being seventy-five miles. The 



aurora forms a ring round the pole, which 

 changes its latitude four times a year. At 

 the equinoxes it attains its greatest distance 

 from the pole, and at midsummer and mid- 

 winter it approaches it most closely ; and it 

 has a zone of maximum intensity which is 

 placed obliquely between the parallels of 

 60 and 70 north. The length of its me- 

 ridional excursion varies from year to year, 

 decreasing and increasing through tolerably 

 regular periods, and reaching a maximum 

 about every eleven years, when, also, its ap- 

 pearance simultaneously attains to its great- 

 est brilliancy. Again, it has its regular 

 yearly and daily movements and periods. 

 At the winter solstice it reaches its maxi- 

 mum annual intensity, and it has its daily 

 maximum. . . . Whether or not there is 

 any connection between auroral exhibitions 

 and the weather is a disputed point. Trom- 

 holt believes that such a relationship is 

 probable. He says that ' however clear 

 the sky, it always became overcast imme- 

 diately after a vivid exhibition, and it gen- 

 erally cleared again as quickly.' Payer de- 

 clares that brilliant auroras are generally 

 succeeded by bad weather, but that those 

 which had a low altitude and little mobility 

 appeared to precede calms. Ross remarks 

 of a particular display that ' it was followed 

 by a fall of snow, as usual.' Scoresby ap- 

 pears to have formed the opinion that there 

 is a relationship indicated by his experience. 

 It is, therefore, allowable to regard the ulti- 

 mate establishment of some connection be- 

 tween these two phenomena as a possible 

 contingency. If, then, we look at the eleven- 

 year cycle of auroral intensity from the me- 

 teorological point of view, it assumes a new 

 interest, for these periods may coincide with 

 the cycles of wet and dry seasons which 

 some meteorologists have deduced from the 

 records of our Australian climate, and the 

 culmination of the one might be related to 

 some equivalent change in the others. For, 

 if a solitary auroral display be followed by a 

 lowered sky, surely a period of continuous 

 auroras might give rise to a period of con- 

 tinuous cloudy weather, with rain and snow. 

 Fritz considers that he has established thi3 

 eleven-year cycle upon the strength of au- 

 roral records extending from 1583 to 18Y4, 

 and his deductions have been verified by 

 others." 



