JI

CORRESPONDENCE.

N.B. We do not hold ourselves answerable for any opinions, expressed by our correspondents.

TO THE EDITOR OF THE ASTRONOMICAL REGISTER.

JUPITER.

SIR,-Now that many telescopes are being turned to this noble planet, the lithographs at the head of this number of the Register will, no doubt, be interesting to many of your readers. Perhaps a few remarks on the more notable features lately seen on the disc will also be acceptable.

Those who had the good fortune to see the fine ellipse, which during the winter 1869-70 lay in the bright southern zone, will not soon forget it. So far as I have been able to learn, it was seen only by Dr. Mayer, in Pennsylvania, and Mr. Crossley and myself at Halifax. I first caught sight of it in November, 1869; Dr. Mayer first saw it on the 5th of January, 1870; and it was last seen here on the 29th of March, 1870.

The planet was carefully scrutinized here in October and November of this year; but unfavourable weather prevented us from obtaining a complete set of drawings. On the 1st of December, however, the proper view was secured; and, although the motion was too great to admit of good micrometric measurements, yet a little patient watching enabled me to make a good sketch. At 11th. p.m., No. I was very faint; but near its western end were two small dark spots.

No. 2 appeared much as it is usually seen.

The zone between bands 2 and 3 was very bright, in fact the only bright zone on the planet at this time.

Near the east end of No. 3 were two dark spots.

Under No. 4 were seen the festoons, but they appeared much flatter than usual. Above No. 4 and near the western edge of the disc was a very large dark spot: it was not nearly so dark as those above named, but had rather the appearance of a detached portion of a broad band. It lay upon No. 5. It was broadest where it was in contact with this band. To the east of this object lay the ellipse; within it was seen a short slightly curved dark line: a pretty dark band was in contact with the upper edge of the ellipse. A very rough measure gave 15" as the length of the longer diameter of this curious object.

On the 4th December, at 10 p m., the new band in the zone between 2 and 3 was very finely seen it had two small dark spots on it.

Soon after midnight this new band nearly filled up the bright zone in which it lay, for it now was seen to consist of a number of very broad detached portions nearly connecting bands 2 and 3 together. At this time No. 5 was a fine broad band, but broader in the middle; and No. 1 had a short curved dark streak upon it.

I

2

Nov. 9th
Oct. 9th

12.30 p.m.

4.30 a.m.

3

Nov. 9th

3.15 a.m.

VENUS.

Sir, In the generally accurate report of the November meeting of the Royal Astronomical Society, contained in your last number, there occurs an error to which I wish to call attention, principally because it enables me to refer to a question of some interest.

In page 277, I am reported to have said, during the discussion on a paper by Captain Noble, that I had seen the disc of Venus all round at her last inferior conjunction in September 25-26. I did not observe Venus on that occasion, and what I did say was that Dr. Winnecke had then seen the whole disc of Venus. His observation is printed in the Astronomische Nachrichten, No. 1863, page 236, and he there states that he was endeavouring to find how far the extension of the horns of Venus could be traced about the time of conjunction. Observing the planet a little before noon on September 25, with a heliometer of 34 lines in aperture, the horns appeared to him to extend over not more than 180° in all, or about half the circumference. "But," he says, "in the moments of greatest steadiness of the image, the whole disc of Venus appeared to be visible. Although the part of the disc not illuminated by the sun appeared very faint in the gray light, yet there was scarcely a doubt in my mind of the reality of the phenomenon." The weather after that day was not sufficiently good to permit Dr. Winnecke to repeat the observation, and he hoped that other observers were more favoured in that respect. "So far," he concludes, " as I know, the observation of the culmination of Venus by Andreas Mayer, at Greifswalde, on the 20th of October, 1759, is hitherto the only one at which the secondary light of Venus has been perceived near the middle of the day."

The question seems to be interesting as to whether or how far this appearance is due to a secondary light of Venus (or a light diffused over her by a highly refractive atmosphere), or to the fact of the darker body of the planet showing its existence as it were by the effect of contrast on the greyish light of the sky as seen in the telescope. I say, "how far," because it is quite likely that both causes may be operative; but, in as far as the effect seen is due to the latter cause, one would suppose that it would be most marked in the part of the disc of Venus which is farthest from the part illuminated by the sun.

I am, Sir, yours faithfully, Blackheath: December 13, 1871.

ENCKE'S COMET.

W. T. LYNN.

Sir, I beg to send you the result of an observation of Encke's Comet, made under peculiarly favourable atmospheric circumstances and possessing, I think, considerable interest.

Sir John Herschel in his Outlines of Astronomy states that "Encke's Comet has no tail." I believe that statement now requires modification. On December 3 I observed Encke's Comet with my 8 inch Browning, with reflector, using a Kellner eyepiece, power of about 60 diameters, the atmosphere being beautifully clear and steady. On first viewing the Comet at a few minutes after 5 p.m., it appeared as the fan-shaped body described by other observers; but, as the twilight diminished and the background became darker, a new feature was apparent. The Comet then presented somewhat the appearance depicted in the annexed sketch. A fan-shaped head from which proceeded, in the opposite direction to the sun, a faint tail, the length of which I roughly estimated at 14 times the diameter of the head. The position angle of a straight line running from head to tail of the Comet was about 60°. The tail was exceedingly faint, the north side decidedly brighter and better defined than the south, the

side seemed continued down, The Comet was attentively

curve bounding the head on the preceding forming the north boundary of the tail. observed till 6'20 p.m., and the sketch is a copy of one made at the telescope.

My instrument is in excellent adjustment, and everything my ingenuity could suggest was resorted to, to prove beyond doubt that the tail seen was a bona fide appendage to the Comet.

At the November meeting of the Royal Astronomical Society, the Astronomer Royal called attention to the fact that "the tail, if there was such an appendage to Encke's Comet, was turned towards the sun, and in right ascension went first." With the greatest deference to such high authority, I think that view can now be proved to be erroneous.

I trust other observers, with more powerful instruments, will be able to confirm my observation.

I should add that unfavourable weather had prevented any observation for a fortnight prior to December 3, and since that date I have been able to examine the Comet only through haze and fog, and clouds of steam from the breweries in this town, not obtaining a clear view of it for a single instant. I am, Sir, your obedient servant, 63, Guild Street, Burton-on-Trent : December 9, 1871.

E. B. KNOBEL.