1372 
foregoing and a circle drawn around the aurora-pole by 
a radius 28° long. The interior circles of the glory are 
‘not seen in this region, but we see sometimes their rays 
cand the exterior rings, less common and less regular. The 
quiet aurora is rare in this region, but the aurora-storms 
and the beautiful drapery-auroree are most usual. 
It is obvious that the frequency of aurora must be dif- | 
ferent in the different regions represented on the map 
(Fig. 7). They must be most frequent in region IV., as _ 
an this we may see both the common glory and the 
edrapery-aurore, which arise at a greater distance from 
the aurora-pole, and probably nearer to the surface of the 
earth. Towards the north this region is bordered by a 
‘belt where aurore must be less frequent, and which, in 
its turn, includes another belt of a maximum frequency 
‘of aurorz, where the arc-aurora must be most common ; 
‘but the drapery-aurore are below the horizon. In the 
circular region around the aurora-pole itself, even the 
common arc is below the horizon, and therefore aurore 
must be rare. Therefore Nordenskjéld observes that his 
map is much like that of the frequency of aurora pub- 
lished by Prof. Fritz (Petermann’s Mitthetlungen, 1874, 
p- 374). Besides, the visibility of auroree depends upon 
the position of the sun, and Nordenskjéld observes that 
it seems that the aurora-arc disappears, or at least be- 
comes invisible, as soon as the sun’s rays illuminate that 
part of our atmosphere where the aurora-ring has its 
seat. Calculating oa this principle a table of the hours 
when the aurora-arc must appear and disappear for an 
observer stationed at the Vega's winter-quarters, he finds 
that the disappearance of the aurora in the morning is 
in accordance with this supposition, whilst its appearance 
in the evening seems to be independent of this cause, as 
it used to appear about nine o’clock. 
As to the relation of aurore to terrestrial magnetism, 
this will be better seen when all the observations of the 
Vega are published. But Nordenskjold remarks that the 
<<cgommon arc,”’ so long as it was not transformed into 
more intense forms of aurora, did not exert on the mag- 
netic needle any influence which might not have been 
included in the usual observations of variations. But 
the more intense aurorz exerted such an influence, and 
when the aurora was on the increase, the declination 
showed a small tendency to a deviation towards the west, 
whilst the intensity varied much: the horizontal com- 
ponent diminished, and the vertical one increased, espe- 
cially as the aurora approached the zenith. 
Nordenskjéld tried also to make some spectral observa- 
tions on aurora, and he observed the usual greenish- 
yellow line, together with a bluish-grey spectrum towards 
the violet end. But the observations were rendered so | 
difficult by the fearful frosts that he could not succeed in 
making more detailed measurements. 
He concludes his most interesting memoir on aurora 
sith the following words :—‘“ When writing this contribu- 
tion to our knowledge of the position of aurore in space, 
I had at my disposal but few former works on this sub- 
ject. I must especially regret that our very rich library 
of travel did not contain the works of Mairans, Bravais, 
Fritz, Loomis, &c. 
that a method of determining the height of aurore 
similar to mine was proposed by Fr. Chr. Mayer (Com- | 
ment. Acad. Scient. Petropolitane, part 1, p. 351, St. 
Petersburg, 1728), and applied, among others, by Tor- 
bern Bergman (Kel. Vet. Akad. Handlingar, xxv., 
Stockholm, 1764, pp. 193 and 249; xxvil. 1766, ip. 224). 
But Bergman arrived at uncorrect figures, as he supposed 
that the centre of the aurora ring is situated on the radius 
of the earth which passes through the pole. Besides, he 
After returning home I discovered | 
NATURE 
preferred to publish at least a general account of the | 
most important features of the observations I made at th: 
Vega’s winter-quarters than to postpone the publication 
for an indefinite time. The want of a larger perusal of 
former literature upon the subject will probably be 
excused to some extent by the circumstance that, when — 
writing this, I had the opportunity of continuously com- 
paring the sketch I have tried to draw with the natural © 
phenomena themselves.” ' : 
. . 
i 
NOTES ‘ 
THE second ascent of Ben Nevis for the winter-was made on 
Saturday last by Mr, Livingstone, Fort William, to read the 
thermometer at the station of the Scottish Meteorological Society — 
on the top of the mountain. The depth of snow was found to 
be much greater at the top than on the occasion of the previous — 
visit. On the edge of the precipices the snow lay to a depth of 
fifteen to twenty feet, the Ordnance Survey Cairn barely over- — 
topping it, and the hut built for the accommodation of Mr. ) 
Wragge during summer being almost completely buried under : 
the snow wreaths. The depth of the snow rapidly diminished 
in the direction of the protecting-cage for the thermometers, — 
outside which it was only three feet deep. Inside the cage, for- 
tunately, there was scarcely any snow, thus leaving the register- 
ing thermometers free. The maximum thermometer read 32°°I, 
and the minimum 13°°2, these being the extremes of temperature 
at the top since the date of the previous visit on December 3 
(NATURE, vol. xxv. p. 135). The temperature at the time of 
the visit, I p.m., was 31°°4 in the cage, and by ¢hermomdtre 
froide, 33°". The spring near the summit was deeply 
buried in snow, but the spring at 2500 feet high was 
open, and the temperature of its water was 37°°3, the air 
at the same place being 41°°o. The temperature of the 
water of the Lake was 42°'1, and that of the air at the same 
height 44°°8. At Fort William the maximum temperature for 
the same day was 53°°5, and the minimum in December 23°°5, 
and in January 26°°8. Hence the temperature at the top had 
fallen only about 10°’o lower than the lowest at the level of the sew 
during the winter. The day was very favourable for the ascent, 
which was made without difficulty. Though it had rained 
heavily at Fort William on the Friday, no fresh snow had fallen 
on the Ben, and as the afternoon sun softened the snow some- 
what, the descent was very easy, the first 2000 feet being done 
in thirty-three minutes. The observations made on these two 
occasions show that as the snow accumulates to such great 
depths near the edge of the precipice, the cbservatory it is 
proposed to erect should be built at some distance from it. 
THE death is announced, on February 8, of Prof. Joseph 
Decaisne, the eminent naturalist, at the age of seventy-five 
years. 
WE regret to announce the death of Adam von Burg, vice- 
president of the Vienna Academy ; she died on February 1, 
aged eighty-five. He was well-known by his mathematical and 
mechanical papers, especially by his ‘‘ Compendium der hoheren 
Mathematik” and ‘* Compendium populeren Mechanik und 
Maschinenlehre.” 
LET ns remind our readers that in connection with Captain 
Abney’s lectures there is an interesting Exhibition of Photo- 
graphic Apparatus and Appliances at the Society of Arts, of 
| which a Catalogue has been issued. The’exhibition will be open 
had no observations upon the common arc, and had only | 
measurements of the larger, less regular ares which are | ° r 
| sion by applying to the Secretary of the Society of Arts. To- 
seen from more southern regions. Knowing how little 
time remains for personal investigation to one who 
returns from a long exploration in unknown tracts, I have 
till February 25 from 10 to 4, and on Wednesday evenings from 
6 to 10. Any one interested in photography may obtain admis 
night there will be a demonstration of photography with artificial 
| lights likely to be of great interest. 
