193 
NATURE ciel 
[Dec. 28, 1882 
of the objects in view. As, in the Italian sky the golden 
orb sank with the dark planet spot on its disk, under brightly 
tinted clouds, shaded off in streaks of tender grey into the 
azure above, with the blue rose-tipped mountains of the Esterets 
beneath,—the scene was one as fascinating in beauty as it was 
interesting in science. All these tints appeared distinctly, albeit 
aintly, in the telescopic image on the card. 
One point was remarkable,—that whilst the shades of the 
mountains were all é/ve, the dark round spot of the planet on 
the sun was almost d/ack. It was the darkest object in the 
field of view. Partly, but I hardly think entirely, this may be 
explained by its being higher, and less subjected to the decom- 
posing power of the lower atmospheric layers. I have en- 
deavoured to represent in water-colours this view of the transit 
of Venus. The result, of course, cannot be reproduced in 
print, but any of your readers who may be visitors at Cannes 
will be welcome to see it, as an original kind of reminiscence of 
a very rare event. C. J. B. WrLiiaMs 
Cannes, December 21 
The Comet during the Last Month 
SINCE my last communication (see NATURE, vol. xxvii. p. 110) 
the weather and the presence of moonshine has been unfavour- 
able for views of the comet; but I have seen it, more or less 
distinetly, on seven nights, from November 22 to December 21. 
I will not take up your space with details, but mention, as the 
general result of these observations, that the comet has become 
smaller in dimensions, and much fainter in its light. With 
moonlight, no trace of a tail is visible; and the nucleus can 
only be discerned by telescope as a nebulous star of third mag- 
nitude, In absence of moonlight, as on December 6, 8, and 12, 
between 2 and 3.30 a.m., the tail was visible to a length of 
about 10°, with a breadth expanding from the head, with no 
distinguishable outline. My last view of it was on the 2oth, at 
3 a.m., when, with a brilliant starlight after moonset, the comet 
was in the south-south-east, about 20° above the horizon, with a 
tail about 8° long, and a nucleus, a nebulous star of third or 
second magnitude. Its position was about as far-to the east- 
north-east of Procyon as that star is east-south-east of Sirius. 
It seems likely to be visible in clear moonless nights for two or 
three weeks longer. C. J. B. WILLIAMS 
Cannes, December 21 
The Heights of Auroras 
THE observations described in your last number as having been 
made long since in Siberia, of lunar halos projected on auroras, 
have not, I believe, been confirmed by other observers; but if 
correct, possibly this phenomenon may be a peculiarity of auro:as 
in (Siberia, or in the Arctic regions. There seems reson to 
think (see Capron’s ‘‘ Aurore,” pp. 37-40) that auroras may be 
lower when near the magnetic pole than further south. If this 
is the case, it is so far favourable to the theory (propoundec, I 
think, by a German writer) described in NATURE (Vol. xxv. 
p- 320), that the auroral zone is a plane, and not part of a sphere 
concentric with the earth’s surface. The majority of the obser- 
vations in lower latitudes cited in Capron’s ‘‘ Aurore,” place 
the phenomenon at a height of 100 miles or upwards. 
The height of the spindle-shaped object seen in the aurora of 
November 17 is thus no argument against its auroral character, 
which I see no reason to doubt. It is true that in my experience 
(which, in this northern part of the country is probably much 
greater than that of your correspondents), I have never seen 
anything resembling it, judging from the descriptions of it ; but 
1 do not think this is a reason for supposing such an auroral 
phenomenon could not take place. The fact that it moved along 
a parallel of magnetic latitude is a very strong argument for its 
auroral character. Besides, its spectrum is stated to have ex- 
hibited the characteristic auroral line. I hope some one will 
collect all possible observations of this beam, especially from the 
continent, and undertake a careful investigation into its path 
and height, T. W. BACKHOUSE 
Sunderland, December 23 
The Aurora and its Spectrum 
In reference to Mr. Ralph Abercrombie’s letter (NATURE, 
vol. xxvii. p. 173), I may mention that his remarks quite accord 
with an opinion expressed to me by my friend, H. R. Procter, 
that the ‘‘aurora is generally formed in some imperfect mist or 
vapour.” Iam intending some experiments on discharges iz 
vacuo under such conditions and reduced temperatures, also on 
phosphorescence, in connection with which M. Lecoq de Bois- 
baudran has shown in his ‘‘ Spectres lumineux,” that we get a 
line in the red, brightening as the temperature is reduced. I do 
not read the result of my Swan lamp experiment, as Mr. 
Munro (same number and page) does, The lamp, when 
perfect, gave quite a bright white glow, with a strong 
carbon spectrum. I should therefore attribute the absence 
of the nitrogen spectrum at this time not so much to a 
high spectrum as to the probability that the lamp had been, as 
far as possible, exhausted of air, and filled with some form of 
carbon gas. Jam not aware of any air-vacuum point at which 
the nitrogen bands or lines disappear, except for want of light 
in the discharge. With regard to the letter of W. M. F. P. on 
the ‘‘ Meteor of November 17th,’ I only assumed the correct- 
ness of the figures and heights quoted in mine for the purpose 
of showing the complex nature of the auroral questions. I am 
not the less perfectly satisfied that the ‘‘beam” was a true 
aurora, and not a meteor, my spectroscopic observation of it 
putting this beyond a doubt. J. RAND CAPRON 
Guildown, December 23 
The Weather 
IT is curious how the recent auroree have been followed not only 
by a cold waye, but by a subsequent warm one, and these respec- 
tively of such extremes, that 21° at 9 a.m. on the r1th is this day re- 
placed by 48° or 27° of difference. Equally strange have been the 
effects on anima] and vegetable life. During the cold, an almost 
Arctic season in its ice-bound stillness prevailed, and a flock ot 
wild geese crossing in front of the house (the forerunners, in 
public opinion, of a hard winter) represented external creature 
life. Now all is changed almost to spring. Roses, though 
somewhat nipped by the frost, seem ready to blow; flies and 
gnats are unthawing, and last night, in goiog up to the observa- 
tory, I noticed the phosphorescent glimmer of a luminous centi- 
pede under one of the shrubs, a sight I do not remember ever 
to have met with in winter before. J. RanD CAPRON 
Gu.ldown, December 19 
A Common Defect of Lenses 
A CHANCE observation a few weeks since led me to the dis- 
covery of a serious defect in the object-glass of the collimator 
of a spectroscope by Grubb, of Dublin, which 1 have been using 
for some time. As further investigation has shown me that the 
defect is very common, while at the same time it is a source of 
considerable error in all experiments on the plane of polarisa- 
tion of polarised light, it seems worth while to cal] the attention 
of readers of Nature to it. The object-yglass in question has 
been imperfectly annealed. As a consequence, a plane polarised 
incident beam is elliptically polarised on emergence from it. 
lf it be looked at between crossed Nicols in a pencil of 
parallel rays, the field of view becomes bright, and is 
crossed by two brushes hyperbolic in form, which for two posi- 
tions of the lens became two straight lines. If again plane 
polarised light be allowed to pass through the lens while it is 
turned round its own axis, there are four positions of the lens 
for which the central portion of the emergent beam is plane 
polarised, and can be quenched by an analysing Nicol ; for all 
other positions of the lens, the emergent beam is elliptically 
polarised, and the light cannot be quenched, but reduced to a 
minimum. Moreover, as the lens is turned, the position of the 
axes of the ellipse varies by nearly half a degree. I have since 
examined a large number of lenses, without finding one quite 
free from the defect. One well-known London optician declines 
to attempt to supply me with a two-inch object-glass which shall 
not show it, while another states he has never known any lens 
absolutely free from it. 
The important bearing of the point on all investigations into 
the palarisation of light is obvious. The consequences it pro- 
duces in modifying the results of some recently-published ex- 
periments of mine (P#z/. Zrans., Part ii., 1882) formed the 
subject of a paper read at the last meeting of the Royal Society. 
R. T, GLAZEBROOK 
Trinity College, Cambridge, December 20 
New Deep-Sea Fish fromjthe_Mediterranean 
My letter in NATURE, vol. xxv. p. 535, called forth two im- 
portant notes from such competent ichthyologists as Mr, J. Y. 
