up to that ring. The whole agreed more with Gr.'s description than B. and M.'s figure, in the progressive shortening of the oblique walls, towards the N., so as to give fairly one-half of the design of a tapering leaf. But my remark at the time was, "the whole object looked coarse, and though curiously arranged, would never have given me the idea of an artificial production." The following night I could still make it out as a previously known figure, and could even count up four valleys in feeble relief. The crater (a) appeared to contain another interior ring, concurrent with the larger one on its E. side. The terminator lay at this time a very little beyond the E. end of Clavius (50), and wall of Bullialdus (60), and its own diameter beyond Copernicus (30). From this it appears that it is by no means a difficult object, and may be made out under much higher illumination than Gr. would have led us to suppose and it is worth looking for, not merely for its curious parallelism, but still more as very suitable for studying the question, which after all seems open to further enquiry, of temporary atmospheric obscuration. It is situated in a region where the effect of variations in perspective foreshortening from libration may be neglected, and since none of the principal lines run in the parallel of latitude, there is little reason to anticipate illusion from the change of the direction of illumination due to the lunar seasons. Any permanent features ought, therefore, to be always equally visible in corresponding circumstances: the direct observations of the discoverer, and the fruitless searches of L., and B. and M., who not only examined but drew the region in detail, would lead to a suspicion that they are not so. Future study only can decide; and if it should be found that there are variations, not explicable by changes in the angles of illumination and vision, we must look further for the cause. The existence of a lunar atmosphere is denied upon arguments of much cogency; but the question cannot be considered as finally at rest; and the region before us may be found especially suited for its decision, since from its low-lying, and at the same time irregular and complicated character it may be supposed highly favourable for the exhibition of atmospheric influence. As such, its strict examination is commended to those who love to trace the footsteps of the Maker of all things in the manifold exercise of His creative power.

TRANSITS OF JUPITER'S SATELLITES.

Oct. 1st. II. egress, 7h. 26m., Ditto shadow, 9h. 8m.3rd. III. egress, 7h. 51m. Ditto shadow ingress, 7h. 52m. Ditto ditto egress, 11h. 29m.-6th. I. ingress, 9h. 25m. Ditto shadow, 10h. 22m. I. egress, 11h. 44m. Ditto shadow, 12h.

42m.-8th. I. egress, 6h. 11m. II. ingress, 6h. 56m. I. shadow egress, 7h. 10m. II. shadow ingress, 8h. 55m. II. egress, 9h. 49m. Ditto shadow, 11h. 46m.-10th. III. ingress, 7h. 44m. IV. egress, 10h. 7m. III. egress, 11h. 22m. III. shadow ingress, 11h. 53m.-13th. I. ingress, 11h. 13m. Ditto shadow, 12h. 18m.-15th. I. shadow ingress, 6h. 46m. I. egress, 8h. Om. Ditto shadow, 9h. 6m. II. ingress, 9h. 22m. Ditto shadow, 11h. 34m. II. egress, 12h. 15m.-17th. III. ingress, 11h. 20m.-22nd. I. ingress, 7h. 30m. Ditto shadow, 8h. 42m. I. egress, 9h. 50m. Ditto shadow, 11h. Im. II. ingress, 11h. 50m.-26th. II. shadow egress, 6h. 22m.-27th. IV. shadow ingress, 9h. 21m.-29th. I. ingress, 9h. 22m. Ditto shadow, 10h. 37m.-31st. 1. egress, 6h. 9m. Ditto shadow, 7h. 25m.

OCCULTATIONS.

Oct. 15th. f Tauri, 4 mag. 7h. 38m. to 7h. 45m.-16th. 02 Tauri, 4 mag., 7h. 25m. to 8h. 9m. 1 Tauri, 4 mag. 7h. 33m. to 8h. 80 Tauri, 6 mag., 7h. 55m. to 8h.36m. 81 Tauri, 51⁄2 5 mag., 8h. 6m. to 8h. 51m. 85 Tauri, 6 mag., 8h. 33m. to 9h. 27m.

THE LUNAR ECLIPSE OF SEPTEMBER 13.

BY JOHN BROWNING, F.R.A.S.

DURING this eclipse several facts were noted that, carefully considered, may, I think, tend to elucidate the interesting problem of the condition or constitution of the Moon's surface. Few questions are more interesting to astronomers, and few seem more difficult of solution.

It is because of their indirect bearing upon this question that I think the points I am about to describe merit particular attention. On the 13th of September the sky during the day was overcast, and it remained thick until shortly before nine o'clock. Then, quite suddenly, it became exceedingly clear, and remained so for the greater part of the night. After the very unfavourable weather astronomers have lately had to contend with, and the tantalizing obscurity which prevailed on the night of the disappearance of the whole of Jupiter's satellites, except in large telescopes, the effect of this almost unlooked-for clearness was most cheering. This exceeding clearness probably materially modified the results that were afterwards obtained.

According to calculation, the eclipse must have commenced

at 9.43, for at that time the Moon entered the penumbra of the earth's shadow; yet, three-quarters of an hour after this, no diminution of luminosity in the Moon could be detected.

At length, at about 10h. 30m., a slight shade was seen stealing gently over the Moon's disk, commencing at the limb in the N.E. quadrant. This shading steadily increased in intensity until eleven o'clock. At this time a darkening of the limb in the N.E. became distinctly perceptible. Three minutes earlier the Moon had entered the umbra of the Earth's shadow ; still, though I was watching most anxiously at the telescope, I could not detect the exact instant at which this, the second stage of the eclipse, began.

The darkness kept creeping over the disk, veiling first one and then another well-known object, until it had covered about one-third of the Moon's surface. When it had reached thus far, many of the craters on the dark limb became distinctly visible. I noticed also that some of the ray-streaks projected within the shadow. At the maximum of eclipse, which occurred at 12.26, three-quarters of the disk seemed darkened; the exact amount was 0.693, the whole disk being 1.

The full disk of the Moon could at all times be dimly made out, the edge of its disk, even the portion most deeply immersed in the shadow, being much brighter than the other portions in shadow, and being, in fact, encircled by a narrow line of light. An observation in close relation to this was made during a late solar eclipse by a very careful observer, Captain Noble. This gentleman noticed that the limb of the Moon, though not the body, was visible, extending some distance beyond the solar disk. What is the meaning of this peculiar appearance? It seems the very reverse of what we might expect to obtain. At the time of an eclipse the Moon is in opposition, and it is, of course, at the full. Under these circumstances we might expect that the centre of the disk would be the most luminous, and that there would be a degradation of light towards the edges.*

The planets Mars, Saturn, and Jupiter also exhibit an increased luminosity at the edges of their disks. This is accounted for by supposing that they are surrounded by clouds. The whole matter would be explained if we could suppose that any vapour exists in the atmosphere of the Moon. Everything, except the appearance I have been describing, points to the contrary conclusion.

A peculiarity of the light reflected from the Moon's surface,

This singular action of the edge of the disk appears to extend to the actinic rays. In one of Mr. Warren De La Rue's exquisite photographs of the full Moon, I noticed that some of the grey plains were continued to the edge of the disk. Frequently they almost touched the edge, but the extreme edge was always marked by a narrow line of light.

apparently in direct contrast with that to which I have just referred, is, that Mr. De la Rue finds that he cannot photograph with facility within some distance from the edge of the terminator. Objects that present the same luminous appearance to the eye as those in the middle of the illuminated portion of the disk, are yet only impressed with a very feeble degree of intensity upon the photographic plate.

Can these facts be of any assistance in reasoning upon the character of the surface of our satellite? For my own part I do not think any person who has been in the habit of observing the Moon with an instrument of large aperture will be able to accept the glacial theory.

When using a telescope of ten or twelve inches aperture, protecting the eye from the great glare by a single-reflecting prism solar eye-piece, the Moon's surface is seen to be almost entirely covered with markings of a considerable variety of tone and colour, many of these frequently changing in a few days, both in shape and hue. Even with an instrument of six inches diameter, some of these changes are easily perceptible.

During the late eclipse, I devoted especial attention to the colour of the Moon. It is a generally received opinion, that when the obscuration has proceeded to the extent of two-thirds or more of the surface, the obscured portion of the Moon appears of a strong coppery red, and that the edge of the shadow on the surface appears of a very decided blue.

In Mr. Norman Lockyer's translation of Amédée Guillemin's "The Heavens," and in Keith Johnston's "Atlas of Astronomy," diagrams of lunar eclipses are painted in chromolithography in the colours I have stated. My observations were made with Mr. Barnes's 10-inch silvered-glass speculum, furnished with a reflecting prism, and an achromatic eye-piece. During the whole time of the eclipse, I could never detect any trace of colour upon the Moon, except what I ordinarily see there. Looking through a four-inch refractor, I also observed the same freedom from colour just noted.

The colour stated to be seen on the part of the Moon under eclipse is usually ascribed to the refraction of some of the solar light as it passes through our atmosphere. I venture to suggest that, when the colour is visible, absorption plays an equally important part in producing it. This absorption would affect principally the blue rays of the spectrum, and it would be very small whenever our atmosphere is free from mist. Now, on the night of the 13th, as I have before said, the air was remarkably clear, and this may possibly enable us to account for the Moon's singular freedom from the colours which seem to have been observed upon it on previous

occasions.

VOL. XII.-NO. III.

Q

Still, as lunar eclipses are tolerably frequent, and, unlike solar eclipses, are visible over half the hemisphere of our globe, I cannot but conclude that such a total absence of colour during eclipses of considerable extent are very rare.

ON COLOURS SEEN DURING THE LUNAR ECLIPSE, SEPT. 13, WITH REMARKS ON THE PRECEDING COMMUNICATION.

BY HENRY J. SLACK, F.G.S., SEC. R.M.S.

Ir was with much surprise I heard from Mr. Browning that his views of the late lunar eclipse through Mr. Barnes's 10-inch telescope, so far from disclosing any decided chromatic effects, led him to express a positive opinion as to their absence. I watched the same eclipse at intervals through a telescope similar to that of Mr. Barnes's, with a silvered mirror, but of smaller size (6-inch), and furnished like his with a right-angled prism, to direct the cone of rays to the eye-piece. On referring to my notes I find the following:-"As shadow came over Aristarchus, that crater remained visible, and rather bright, until shadow advanced to near Eratosthenes, when it required sharp looking for to see it. The shadow was inky purple, and the sky colour in the neighbourhood dusky red. As shadow passed over different portions of the Moon, the darkness varied considerably, being much less over highly-reflecting portions than over the seas, which became very dark. After twelve the eclipsed limb grew noticeably redder, and objects likewise became gradually more visible. The red, coppery tint chiefly affected the lower part of the obscured limb, but was visible further in, gradually blending with the inky tints presented by the umbra at its advancing edge. By twenty minutes past twelve the increased visibility of obscured parts very striking. 12.26, eclipse at its height, and visibility of objects in obscured parts much greater than at an earlier period. As the Moon passed out of shadow, a brightening took place in opposite directions at the two edges of the limb, and bluish tints of brighter hue became conspicuous, contrasting with the reds." I added to this, "Red colour less conspicuous in telescope than in opera-glass with two-inch lenses." My wife's report of what she saw generally agreed with mine, but she noticed a greenish tint at the beginning of the eclipse in the penumbra, and did not see the blue as much as I did towards its termination. I think her eye is more sensitive than mine to the peculiar