Dr. LEE, President, in the Chair.

Rev. J. Morton, Clifton;

J. F. Beckett, Esq., R.N.;

Rev. E. K. Elliott, Broadwater; and

N. Martindale, Esq., Holmfield, near Liverpool, were balloted for and duly elected Fellows of the Society.

On a Re-discovery of the missing Lunar Crater, Alhazen, situated on the western border of the Mare Crisium. By W. R. Birt, Esq.

The Rev. T. W. Webb, in his interesting catalogue of lunar objects, speaks thus of this crater:

"On the western edge of the Mare Crisium, Schröter delineated a crater, called by him Alhazen, which he employed to measure the existing libration: he saw in it, after a time, unaccountable changes; and now it is said it cannot be found. Beer and Mädler think he confounded it with a crater lying further south; the question, however, which in the interim was debated between Kunowsky and Köhler, is not quite cleared up."

Having obtained a view, in January last, of two objects. which appeared to me to have given rise to Schröter's remarks, I communicated my observations to Mr. Webb, and have lately received from that gentleman the following historical notices af Alhazen, bearing especially on the variability of its aspect:

"Schröter had watched and measured from it for years, and found it too varying in aspect to be accounted for by the varying angle of illumination. At first it was a depressed surface, surrounded by a ring, and distinguished from the

neighbouring objects under all angles by its dark grey tint. Subsequently it often appeared, even in a 27-foot reflector (mirror about 20 inches), under favourable circumstances, as a bright longish flat mountain, though more frequently in its original grey aspect; occasionally it would be so indistinct, other objects being well defined, that he could not tell what to make of it. 1797, March 1, Alhazen being very near the limb (only 27" 27 from it), and therefore in a position to be very indistinct, especially as the terminator had advanced to the other side of the Mare, he saw it with a 13-foot reflector (mirror about 9 inches and power 180) more distinctly than ever, and in quite a new form, as a real, very deep, and bright crater, with an irregular ring scarcely united to the south, and open to the north, with a projection on the east side. Also there was a small shadow, as of a crater never seen before during the innumerable observations of ten years. Schröter thought Alhazen, under this aspect, appeared as deep as Proclus."

Mr. Webb enclosed a tracing, with this remark: "I think you will consider it as affording an interesting comparison with your own observations. He has figured, you

will see (as well as described), a little crater where you describe two (?).' The circumstance of his ranges uniting so closely to the south may be due to a different libration."

Kunowsky, in the Astronomische Jahrbuch for 1825, speaks of Alhazen as lost. In the Jahrbuch for 1826, Pastorff, writing January 20, 1823, says his son repeatedly found Alhazen. Pastorff also saw it (see p. 250 of the same Jahrbuch).

In the Jahrbuch for 1827 (p. 135), Harding is recorded as having seen Alhazen as Schröter had drawn it. Pastorff saw it in the same year, and in 1829.

The difference of aspect, as well as the occasional difficulty of finding this interesting spot, is highly curious. Schröter's earliest delineation gives it, as described, a shallow depression, entirely surrounded by a ring. My own observations, which now follow, may perhaps throw some light on these differences and difficulties. Two ranges of mountains, one behind the other, may easily be taken for a crater, and at a certain angle

of illumination it may be exceedingly difficult to distinguish the difference. After a while the supposed crater entirely vanishes; libration alters the visual angle, and rotation the illuminating one, the observer being greatly puzzled as to what has become of his well-recognised crater.

1862, Jan. 3d 4h 45m to 6h om, Moon's age 3d.1, the terminator passing through the Mare Crisium a little west of Picard, the floors of Cleomedes, Burckhardt, Geminus, and Bernouilli being in deep shadow, the Promontorium Agarum was very distinct, and in fine relief, and the craters Condorcet, Hansen, and Alhazen of Beer and Mädler exceedingly well marked; the Alhazen of Schröter also very distinct, and Eimmart between it and Cleomedes well seen.

Schröter's Alhazen, at first sight, appears to have somewhat the appearance of a crater, the west edge being high, but the east much lower. Upon attentively considering it, I have some reason to think that it consists of two nearly parallel ranges of mountains just on the borders of the Mare, the eastern range forming a part of the actual border. The shadow of the western range is (under this illumination) terminated at a line west of the eastern range, the western slope of which is glowing in bright sunshine. The mountain south of Alhazen, also figured by Schröter, is exceedingly distinct, and stands on the border of the Mare.

From the circumstance of not finding a distinct crater in this part of the border of the Mare Crisium when the evening shadows set in and the terminator sweeps over the western border of the Mare, combined with the surface of the Mare running in amongst the mountains on the west of the Mare, I am the more inclined to consider the appearance of a crater to be produced when the shadow of the western range falls short of the eastern.

1862, Jan. 4d 5h 30m to 7h 16m, Moon's age 4d1, terminator obliquely through Atlas. Oersted, Cepheus, Franklin, and Berzelius, with Promontorium Archideum, form a fine chain between Atlas and Geminus.

At times the definition has been very fine, and the real character of Schröter's Alhazen well seen; the southern termination of the two mountain-ranges was seen to be quite separate the one from the other, and the level surface passing between them. It is not surprising that the two combined should have been regarded as a crater, especially if viewed by a low power; for now, haze coming on, it is impossible to distinguish the two from a crater. In the earlier part of the evening the independence of the two ranges, especially on the south, was very apparent: the shorter shadow brought out very distinctly the mountain character, and the recess of the shadow of the eastern range revealed the existence of two (?) small craters lying at the foot of the eastern slope, upon the very border of the Mare Crisium. Beer and Mädler figure two mountain-ranges in the locality, but very unlike the mountain ranges described above.

Note on a dark, circular Spot upon the Sun's Disk, with rapid motion, as observed by W. Lummis, Esq., of Manchester, 1862, March 20. By J. R. Hind, Esq.

In a letter addressed to me on the 20th of March, by W. Lummis, Esq., of the Manchester, Sheffield, and Lincolnshire Railway Company's Office at Manchester, it was stated that on the morning of the same day, while examining the Sun's disk with a telescope of about 2 inches aperture, he had remarked a small black spot more regular and better defined than usual. He watched it about 20 minutes, during which time it had moved rapidly, as shown in a diagram accompanying his letter,

233,234 maintaining its round form: Mr. Lummis called a friend to see it, who remarked it as distinctly as himself.

On applying for further information with reference to his observation, Mr. Lummis wrote me, "As to the positions of the spot I regret that I cannot give them with much more precision than shown in the rough sketch sent to you, which was taken from one made at the time I witnessed the transit. I had no instrument but the telescope, and I measured with a small strip of card the distances of the spot from the Sun's edge. From the time when I first observed it, 8h 28m A.M., (Manchester time) to 8h 50m, the spot had moved over about 12′ of arc, as nearly as I can judge by the eye, and its size or rather apparent diameter I should take to be about 7". The telescope is 24 inches in aperture and magnifies 80 times. I had for several mornings been observing the Sun, which I noticed was particularly free from spots. Only one small one could be detected by me on the morning of the zoth, just below the spot marked A on the sketch.* I regret extremely having been compelled to leave before the object had completed its transit, as I should have wished to have witnessed its egress." On carefully reading off from Mr. Lummis's sketch the differences of azimuth and altitude of the spot and Sun's centre, and converting them into differences of longitude and latitude, I find the following numbers,

Considerations on the Solar Spots. By M. Eugene
Jeanjaquet.

The author refers to his work, Phénomènes Célestes résultant de la Transmission successive de la Lumière, published in 1859, as containing the following evident proof that the solar spots, whatever their nature may be, are not the appearances (les aperçus) of an obscure nucleus, situate in the centre of the photosphere, and consequently that there is no reason for believing in the existence of such a nucleus. "Si le soleil," he said, "était composé tout à la fois d'une noyau solide et d'une triple enveloppe gazeuse concentrique à ce noyau, si mince que fût cette enveloppe elle n'en augmenterait pas moins l'astre de son épaisseur; il y aurait par conséquent sur tout le pourtour du disque une bande circulaire sur laquelle aucune tache ne pourrait se montrer; en d'autres termes, ce n'est qu'à une certaine distance, en dedans du disque, que des taches pourraient se laisser voir. Or, les taches commencent et finissent avec les bords mêmes du soleil; *The first position of the moving spot.

233, 234

"Mais les taches solaires commencent-elles et finissent

*

Il

elles réellement sur les bords de l'astre radieux? Il semble, tant la chose est suffisamment établie, que je pourrais me dispenser de faire cette question. Il s'en faut de beaucoup cependant que je ne doive pas la soulever. Suivant quelques observateurs, l'enveloppe solaire, dans l'hypothèse du globe central obscur, est excessivement peu épaisse; elle n'aurait de profondeur, d'après M. Secchi, que dans la minime proportion de quatre millimètres sur un globe d'un mètre de rayon.* est vrai de dire que M. Secchi, tout en faisant l'enveloppe solaire si mince, ne prétend pas imposer de tous points sa manière de voir. Il déclare lui-même que son opinion n'a rien d'absolu, puisqu'elle est le résultat d'une seule observation, et qu'il existe probablement des ouvertures plus profondes que celle qui lui a servi de mesure. Quoiqu'il en soit, l'enveloppe aurait dans tous les cas très-peu d'épaisseur. Or, une aussi mince enveloppe, si elle existe, réporterait naturellement les taches très-près des bords du soleil, si près même de ces bords que leur lieu d'apparition et de disparition ne pourrait souvent être constaté qu'avec la plus grande peine; partant, que l'on n'aurait absolument aucune assurance qu'un globe solide ne se trouvé pas en définitive au centre de l'astre du jour La question de savoir si véritablement les taches naissent et s'effacent sur les bords du soleil est donc discutable, et elle mérite certainement d'être discutée.

"Puis, il y a une autre question, se rattachant à l'existence des taches aux extrémités du disque solaire, qui mérite aussi

d'être étudiée. Des. entailles ont été vues occasionnellement

sur le limbe du soleil, et ces entailles n'ont pas tardé à être suivies de taches. Est-ce que de semblables faits n'impliquent pas nécessairement des ouvertures dans une enveloppe, et au fond de ces ouvertures le corps intérieur de l'astre radieux?

"Je m'empresse de le dire; en ce qui touche la mince enveloppe du soleil, assez d'apparitions et de disparitions de taches ont été constatées pour qu'il ne puisse pas y avoir de doute sur le lieu où ces apparitions et disparitions s'opèrent. Ceux qui, depuis Galilée jusqu'à nos jours, ont longuement et patiemment examiné le soleil pour déduire du mouvement de ses taches le temps de sa rotation, ne nous auraient point donné le temps de cette rotation s'ils n'avaient pas vu des taches naître et mourir aux bords mêmes de l'astre lumineux. On ne lit dans les écrits d'aucun observateur que les taches commencent et finissent en dedans du limbe solaire, tandis qu'il n'est pas un auteur un peu compétent qui n'enseigne qu'elles apparaissent et disparaissent sur les bords mêmes de l'astre. Toutes nos connaissances sur le mouvement des taches seraient vaines, si les instants d'apparition et de disparition de ces étranges figures, aux limites extrêmes du soleil, ne nous étaient pas parfaitement connus. Que de choses, en revanche, ne saurions-nous pas sur le prétendu globe obscur, sur sa grandeur, sa distance à l'astre de lumière, etc. etc., si toutes les taches commençaient et finissaient en dedans du disque, à une distance des bords régulièrement la même ! Nous ne savons pas ces choses, du moins nous ne les savons pas comme nous devrions les savoir; les taches ne se lèvent ni ne se couchent donc point, pour ainsi parler, à l'intérieur du disque solaire. Ainsi, on peut-être parfaitement tranquille, les taches apparaissent bien au bord oriental du soleil, et elles disparaissent bien à son bord occidental; rien n'est plus certaine que ce fait-là.

"Au surplus, des taches naîtraient et mourraient régulièrement à une certaine distance en dedans du disque du soleil (ce que les observations n'indiquent point, mais que j'admets ici un

* Astronomische Nachrichten, No. 1148, p. 307.

234, 235

instant par voie de supposition), des taches, dis-je, naîtraient et mourraient régulièrement en dedans du disque solaire, à une courte distance des bords, que même une semblable circonstance, à moins que les taches ne fussent grandes, fortes, bien distinctes, ne serait nullement conclusive de l'hypothèse du globe central obscur, puis qu'on pourrait toujours objecter que les taches disparaissent par l'effet de l'éloignement: ne sait-on pas combien les noyaux se rapetissent à mesure qu'ils s'éloignent du centre du soleil, combien ils grandissent au contraire à mesure qu'ils s'approchent de ce centre?

"J'arrive aux entailles qui se voient occasionnellement sur les bords du soleil et qui ne sont naturellement autre chose que de fort grandes taches, tout noyau sur le limbe solaire y proSi ces entailles se duisant nécessairement une échancrure. montrent en noir, on comprend que mon opinion s'en trouve fortifiée; et c'est bien en noir qu'elles se montrent. Mais il paraît qu'il y a à cette règle des exceptions et qu'en de certaines occasions, excessivement rares d'ailleurs, des entailles ont été vues béantes; c'est du moins ce qui semble surtout ressortir d'une grande échancrure que M. Lawson a observée le 30 Juin, 1846, sur le bord oriental du soleil, échancrure à laquelle une tache noire n'aurait pas tardé de faire suite. Une entaille béante suivie immédiatement d'une tache! Une ouverture

photosphérique avec un noyau à sa base! Quelle plus grande preuve pourrait-on donner de l'existence d'un globe central obscur! Heureusement que pour répondre à cette formidable objection, nous avons l'exemple de la lune dans les éclipses de soleil. La lune aussi lorsqu'elle échancre le soleil, fait sur lui une entaille libre, et ce n'est jamais que lorsqu'elle le recouvre en entier qu'elle se révèle en noir: pourquoi un noyau de tache, s'avançant sur l'astre de lumière, ne se conduirait-il pas, toutes proportions gardées, de la même façon que notre satellite?* Ainsi, bien loin qu'une entaille béante indique une ouverture sur le bord de l'astre, on peut dire qu'une semblable échancrure est une preuve de plus de l'existence des taches aux extrêmes limites du disque du soleil."

"Neuchâtel (Suisse), le 28–30 Mars 1862."

On the Transit of Mercury of 12 Nov. 1861, observed at Hobart Town. By Mr. Abbott.

I transmit a diagram of the transit of Mercury, which occurred on the 12th of the present month. The time of ingress stated may not be quite as correct as I could have wished, from the following circumstances,

To make sure of true time I had taken a transit at noon on the same day; on that point, therefore, I considered myself well prepared for the occasion.

A short time before the immersion, I had erected a 5-foot telescope on one of Varley's stands, and at the very point of the planet's contact, one of the bands gave way, which caused at that critical moment a slight confusion, until I could get the telescope tube remounted on a fresh stand; notwithstanding this accident I consider the time given a close approximation.

The afternoon on the whole was favourable, and had it not been for Mount Wellington (4240 feet high) blocking out our

"On n'a pas suffisamment fait attention, à mon avis, à tout ce qu'il y a de remarquable dans cette manière d'agir de la lune, parfaitement invisible tant qu'il reste une parcelle de lumière solaire, et, une fois le dernier filet de lumière supprimé, se montrant immédiatement en noir."