chain of mountains, connecting "Babbage" with Anaximander, forms the eastern boundary of the table-land. Beer and Mädler have left its boundaries undetermined, and further observations are necessary to mark them out with precision.

Eye-sketch of a chain of Lunar craters, with three large unnamed and unrepresented craters, taken at Hartwell on the morning of Sept. 18, 1862.

I. Philolaus (Riccioli). A ringed mountain.

II. Anaximenes (Riccioli). A ringed mountain.

III. An unnamed crater on Beer and Mädler's map. It is marked "Sommering" by Le Couturier. Beer and Mädler have another "Sommering" near the centre of the disk.

IV. Anaximander (Riccioli). The ring of this crater is imperfect, and requires further observation to define its outline accurately. Between it and V there is a well-marked mountain, besides other interesting features.

V. Herschel II. (Birt). An extensive depression of the character of a walled plain, with a nearly perfect ring not shown by Beer and Mädler, who describe the region between Horrebow, Anaximander, and Fontenelle as an exceedingly rich crater country; the principal part consisting of the region of Herschel II. The following features are common to the eye-sketch and Map:

B. A high mountain mass marked Anaximander B by Beer and Mädler. It really forms the north angle of the wall of the large depression Herschel II. e. A mountain mass forming the N.W. angle of the ring of Herschel II. f. A crater exterior to Herschel II.

c, d. Two craters in the line of eruption that crosses Herschel II. in a curvilinear direction.

The eye-sketch shows the general direction of this eruptive line from the portion of the ring that is absent to a crater east of Horrebow (X). It is not shown on the German map.

VI. The table-land "Robinson" (Birt).

A, B, and C. Craters on the table-land.

E. A steep mountain steppe on the south, not shown in the sketch, dipping to the depression "South." It contains the three dark mountains of Beer and Mädler.

F. A steep mountain "steppe" on the north, dipping to Herschel II.

E and F were observed and figured by Schröter in his 'Selenotopographische Fragmente,' T. xxvi. fig. 1.

VII. A depression south of the table-land "Robinson." Proposed name "South" (Birt). The central crater D is shown by Beer and Mädler.

VIII. Another depression eastward of "South," and between it and Pythagoras. The crater A on Beer and Mädler's map is really nearer the west border than shown in the eye-sketch. Proposed name "Babbage" (Birt).

Schröter observed this walled plain. Figures of it, with the interior crater A close to the western edge, are given in T. xxvi. (figs. 1 and 2) of his 'Selenotopographische Fragmente.' It would appear that he designated it "Pythagoras," the crater now bearing that name being termed Pythagoras borealis. By far the most suitable name for the large crater with the central mountain is that on the large

German map, "Pythagoras;" while to prevent misapprehension as to the western walled plain with the included crater, and to distinguish it from the eastern crater, it is proposed to call it "Babbage."

IX. Pythagoras (Riccioli). The largest and most magnificent crater in this part of the moon, showing itself as a conspicuous object with its central mountain, when nearly the whole of the previously-described craters and walled plains are lost to view.

X. Horrebow (Schröter). This crater, which pierces the S. W. angle of the rim of Herschel, has hitherto been treated as being independent of any other formation. Schröter, who named it, figured it in its proper position at the west of the mountains F, and he gives (see T. xxvi. fig. 1, above referred to) the chain of mountains, omitted by Beer and Mädler, forming the continuation of the rim from the steep mountains F to the rim of Anaximander, where he gives a small crater shown in the eye-sketch. On the other hand, Schröter has omitted the western rim extending northwards from Horrebow, which is given by Beer and Mädler. Horrebow is clearly a part of Herschel II.

Schröter does not appear to have recognized or figured "South."

On the Augmentation of the Apparent Diameter of a Body by its Atmospheric Refraction. By the Rev. Professor CHALLIS, M.A., F.R.S., F.R.A.S. For reasons given in another communication, it was assumed that atmospheres generally have definite boundaries at which their densities have small but finite values. Two cases of refraction were considered: in the one, the curvature of the course of a ray through the atmosphere was assumed to be always less than that of the globe it surrounds; and in the other, the curvature of the globe might be the greater. The former is known to be the case with the earth's atmosphere; and it was supposed that, à fortiori, this must be the case with respect to any atmosphere the moon may be supposed to have. On this supposition it was shown that the apparent diameter of the moon, as ascertained by measurement, would be greater than that inferred from the observation of an occultation of a star, because, by reason of the refraction of its atmosphere, the star would disappear and reappear when the line of vision was within the moon's apparent boundary. The same result would be obtained from a solar eclipse. It was stated that, by actual comparisons of the two kinds of determinations, such an excess to the amount of from 6" to 8" was found. This difference may reasonably be attributed to the existence of a lunar atmosphere of very small magnitude and density. The author also stated that from this result there would be reason to expect, in a solar eclipse, that a slender band of the sun's disk immediately contiguous to the moon's border would be somewhat brighter than the other parts, and advised that especial attention should be directed to this point on the next occurrence of a solar eclipse. The case in which the curvature of the path of the ray is greater than that of the globe was assumed to be that of the sun's atmosphere; and it was shown, on this supposition, that all objects seen by rays which come from the sun's periphery are brought by the refraction to the level of the boundary of the atmosphere, whether they proceeded from objects on the surface of the interior globe, or from clouds supposed to be suspended in the atmosphere. Accordingly, the contour of the sun should appear quite continuous, and the augmentation of apparent semidiameter will be equal to the angle subtended at the earth by the whole height of the atmosphere. The apparent diameters of the planets will, for like reasons, be augmented to a certain amount by their atmospheric refractions; and on account of the great distances of these bodies from the earth, the eclipse of a satellite will take place as soon as the visual ray is bent by the interposition of the atmosphere.

On the Zodiacal Light, and on Shooting-Stars.

By the Rev. Professor CHALLIS, M.A., F.R.S., F.R.A.S.

The phenomena of the zodiacal light, as gathered from observations made both in northern and in southern latitudes, were stated to be as follows. As seen in north latitudes, it appears in the West after the departure of twilight, as a very faint light,

stretching along the ecliptic, about 10° broad at its base in the horizon, and coming to an apex at an altitude of from 40° to 50°. It is most perceptible in the West in the months of February and March, at which time its apex is near the Pleiades. Similar appearances are presented in the morning before sunrise in the East in the months of August and September. The light seen in the autumn lies in the same direction from the sun as that seen in the spring. In the southern hemisphere the appearances are strictly analogous, but the times and positions of maximum visibility are, the evenings in autumn in the West, and the mornings in spring in the East. The portion best seen in the southern hemisphere lies in the opposite direction from the sun to that which is best seen in the northern hemisphere. The portion seen, and the degree of visibility, depend on the inclination to the horizon of the part of the ecliptic along which the light stretches. The greater the inclination the better it is seen. At the December solstice opposite portions have been seen in the northern hemisphere, one in the morning and the other in the evening; and in the southern hemisphere opposite portions have been similarly seen at the June solstice. At these seasons the ecliptic is inclined at large and equal angles to the horizon at equal intervals before sunrise and after sunset. The southern observations, from which these inferences are drawn, are those made by Professor Piazzi Smyth at the Cape of Good Hope in the years 1843, 1844, and 1845, and published in vol. xx. of the Edinburgh Transactions,' and evening observations in the autumn of 1848, communicated by a friend of the author resident in the interior of Brazil. More recently, in vol. iv. of the American Astronomical Journal' were published observations by Mr. Jones, a chaplain of the United States Navy, who makes the following statement:-"When in latitude 23° 28′ N., the sun being in the opposite solstice, I saw the zodiacal light at both east and west horizon simultaneously from eleven to one o'clock for several nights in succession." The ecliptic must at the time have nearly passed through the zenith of the observer at midnight. It is clear, therefore, that to be seen an hour before and after midnight, the zodiacal light must have extended beyond the earth's orbit. Taking this as a necessary inference from the observations, it follows that the earth is either always enveloped by the zodiacal light, or at least when passing through the line of its nodes. Professor Challis considers this to be the explanation in part of the luminosity of the sky which is generally perceptible on clear nights, and at some seasons in greater degree than at others. The American observer also states that he saw when at Quito, "every night, and all through the night, a luminous arch from east to west quite across the sky, 20° wide, and most apparent when the ecliptic is vertical." This light is distinguished from the zodiacal light by its being of uniform width. From the ensemble of the observations, the zodiacal light is of the form of a double convex lens, with the sun in the centre, and the principal plane coinciding nearly with that of the sun's equator. As it may be inferred from the foregoing statements that it envelopes the earth, we may conclude that it is simply luminosity, without accompanying bodies. Professor Challis proposes, therefore, to account for it by the effect which the rotation of the vast body of the sun produces on the luminiferous medium, this effect being rendered visible by the disturbance of the gyratory motion by the motion of translation of the sun in space. In a similar manner, magnetic currents are rendered visible in the form of the aurora by the effect of transverse currents. This explanation he stated to be in accordance with the principles of the undulatory theory of light.

The appearance of shooting-stars in the August and November periods was accounted for on like principles, by the disturbance given to the luminiferous medium by the curvilinear motion of the earth resulting from its proper motion and the motion of the solar system through space. At two epochs depending on the variations of the rate of motion, and of the rate of deviation from rectilinear motion, the disturbances would be at a maximum, and these two epochs were assumed to correspond to Aug. 10 and Nov. 12. The kind of disturbance which the earth impresses by its curvilinear motion was supposed to be such as would produce eddies or whirls. Besides this, there might be a disturbance of terrestrial origin, analogous to that which produces the zodiacal light, which might account for the luminous arch noticed by the American observer.

On some of the Characteristic Differences between the Configuration of the Surfaces of the Earth and Moon. By Professor HENNESSY, F.R.S. The author pointed out that the peculiarities observed on the surface of our satellite should be ascribed to the sole action of volcanic forces, whereas those which we find on the earth result from a combination of volcanic and atmospherical agencies. In order more perfectly to study these contrasts, he called attention to the most characteristic feature of all lunar volcanos, namely the ring- or hoop-shaped crater, surrounded by circular, nearly concentric ridges. On the earth's surface, volcanos deviated more or less from this type; and if the deviations are due to the differences between terrestrial and lunar superficial forces, it must follow that such differences will be most distinctly manifested in those cases where such terrestrial forces possess the highest degree of energy. He illustrated this proposition by referring to the peculiar structure of the volcanos in the island of Java, where the action of tropical rains and hurricanes has been effective in producing the widest differences between the terrestrial volcanic summits and those observed on the moon's surface. While the hooped structure of the latter cannot be traced among the views of Javanese volcanos which are presented in the comprehensive work published by Dr. Junghuhn, we frequently find diagrams of volcanic cones showing radiating ribs like those of a folded lamp-shade or an umbrella half closed, an appearance due to the very regular manner in which the tropical torrents scoop out the friable and scoriaceous summits of the craters. The contrast which arises by comparing some of these drawings with the best lunar diagrams and photographs may prove highly interesting to geologists as well as to selenographers.

On a Brilliant Elliptic Ring in the Planetary Nebula, AR 20° 56', N.P.D.101° 56'. By WILLIAM LASSELL, F.R.S.; in a Letter to Dr. LEE, F.R.S.

9 Piazza Sliema, Malta, 26th Sept. 1862.

MY DEAR SIR,-In directing my large equatorial upon the well-known planetary nebula situated in R 20h 56m, N.P.D. 101° 56′ (1862), it has revealed so marvellous a conformation that I cannot forbear to send you a drawing of it, with some description of its appearance. With comparatively low powers, e. g. 231 and 285, it appears at first sight as a vividly light-blue elliptic nebula, with a slight prolongation of the nebula, or a very faint star at or near the ends of the transverse axis. In this aspect the nebula resembles in form the planet Saturn when the ring is seen nearly edgewise. Attentively viewing it with higher powers, magnifying respectively 760, 1060 and 1480 times, and under the most favourable circumstances which have presented themselves, I have discovered within the nebula a brilliant elliptic ring, extremely well defined, and apparently having no connexion with the surrounding nebula; which indeed has the appearance of a gaseous or gauze-like envelope, scarcely interfering with the sharpness of the ring, and only diminishing somewhat its brightness. This nebulous envelope extends a little further from the ends of the conjugate than from the ends of the transverse axis; indeed it is but very faintly prolonged, and only just traceable towards the preceding and following stars. There is a star near its border northwards, in the projection of the conjugate axis.

The breadth or thickness of the ring is, unlike that of Saturn, nearly uniform or equal in every part, so that its form most probably is either really elliptic, and seen by us in a line nearly perpendicular to its plane; or if really circular and seen foreshortened, a section through any part of it limited by the internal and external diameters must be a circle. In other words, it will be like a circular cylinder bent round. It could scarcely fail to bring to my mind the annular nebula in Lyra, especially as there is a conspicuous central star (proportionally, however, much brighter than that which is in the centre of that nebula); and yet the resemblance is only rudely in form; for this ring is much more symmetrical and more sharply defined, suggesting the idea of a solid galaxy of brilliant stars.

The ring is not perfectly uniform in brightness, the south-preceding part being slightly the most vivid. The transverse axis is inclined to the parallel of declination about 13°. A series of micrometrical measures of the length and breadth of

the ellipse, gives a mean of 26"-2 for the transverse, and 16"-6 for the conjugate

axis.

The accompanying drawing has not been at all corrected by these measures, but is the result of several sketches made during different observations, and is a faithful transcript of the appearance of the nebula to my eye, when most favourably seen.

The object is, as may be supposed, one of extreme difficulty, requiring in the highest degree the combination of light and definition in the telescope, and a favourable state of atmosphere,-which will further appear when I state that it was not until I was favoured with an unusually fine night, and had applied a power of 1480, that the whole of the details were brought out.

I confess I have been greatly impressed by the revelation of this most wonderful object, situated on what perhaps we may consider as the very confines of the accessible or recognizable part of the universe, affording ground for the inference that more gorgeous systems exist beyond our view than any we have become acquainted with. I am, &c., W. LASSELL.

Observed R.A. and N.P.D. of Comet II. 1862.

By the Rev. R. MAIN, M.A., F.R.S.

This paper gave the results of observations of the comet from August 5 to August 29, on ten nights. It was observed on the meridian with the Carrington transitcircle on August 7 and 9, and off the meridian with the heliometer, used as an ordinary equatorial, on August 5, 7, 9, 14, 18, 19, 22, 23, 25, and 29. The observations have been rigorously reduced, and all necessary corrections for refraction, parallax, &c. have been applied. The assumed mean places of the companion stars for 1862, January 1, taken mainly from the Radcliffe Catalogue of Circumpolar Stars,' were also given.

On the Dimensions and Ellipticity of Mars.

By the Rev. R. MAIN, M.A., F.R.S.

The

This paper gave the results of seven sets of measures of the disk of Mars, made for the determination of his ellipticity with the heliometer, by the method of contact of limbs of the two images formed by the half-object-glasses. The power used was 300, which is found by experience to be very suitable for such measures. direction of the polar diameter was determined by a well-defined circular white cap near the southern limb, the centre of which was assumed to be coincident with the South Pole. The directions, separately estimated, of the polar and equatorial diameters agreed well on separate evenings, their difference never deviating much from 90°, thus proving the precision of the estimations. The measured diameters have been corrected for defect of illumination. The following are the results of the measures:

Mr. Main drew particular attention to the difference in the degrees of consistency in the results for the polar and for the equatorial diameter, the latter agreeing sur