the nature of fissures. They, with the circular range, have only been observed once. (See key-plan, fig. 1.) VI. i.-The westernmost of the two oval markings. VII. k. The easternmost of the two oval markings. Schröter appears to have observed them on December 11, 1788: he has figured them on t. xxi. fig. 6. They have been observed by the writer on fifteen or sixteen occasions at least. VIII. p.-A bay-like indentation in the north-east rim seen under the mid-day illumination. It has been observed on five occasions. It is not shown in the key-plan, but its locality is indicated by the letter p. This indentation, which is best seen about full moon, or about fifteen or sixteen days of the moon's age, marks, I apprehend, the form of the rim of Plato hereabout. It is well shown in a sketch by Webb, under date of 1855, October 24, ten to eleven hours; the sketch is preserved in the volume of Observations on Plato deposited in the library of the Royal Astronomical Society. It is approximately figured at p, detached from the key-plan of the crater, as it is only visible for about two days near the full. IX. q.-A short, light spur in the neighbourhood of p, which, with the shadow within the cavity i, appears to indicate the existence of a ledge or terrace in this part of Plato. It has only been observed once. X. 4.-A bold rock jutting into the interior, casting a well-defined shadow eastward in the morning and forenoon, and westward on the floor of the crater towards sunset: it is more frequently observed as the eastern extremity of the longest diameter of the apparent ellipse. This rock is one of the finest and most conspicuous objects in the neighbourhood of Plato during the morning illumination, glowing in the rays of the sun like molten silver. From about 7.5 to 8.5 days of the moon's age, it is seen as a very brilliant point at the eastern extremity of the crater; during the next two days (from 8.5 to 10.5 days of the moon's age) it is very distinguishable, standing out as a bold rock, and casting a well-defined shadow eastward; during the next three days (from 10.5 to 13·5) it loses its shadow, but continues a perceptibly bright object, imparting to the eastern extremity its peculiar brilliancy at this age of the moon. It is now lost for some time. About nineteen days of the moon's age it has been seen very distinctly; two days later, viz. at twenty-one days, its shadow has been seen on the floor of Plato; and about this time, or rather later, it has been seen standing out in fine and bold relief, a magnificent object, its height above the general altitude of the ring being apparent not only by the acuminated character of its shadow on the floor of the crater, but by its towering considerably above the general summit. It appears to be a formation in a measure distinct from the ring itself, and greatly allied in its character to that of Pico on the south of Plato; indeed, it deserves as conspicuous a position on a map as Pico. It possesses two bold spurs on the north-east and southeast. Its very appearance is exceedingly suggestive, especially when taken in connexion with a formation immediately south of it. Both should be most carefully and scrupulously watched, in order to determine if any degrading forces are at work hereabout. This rock has been observed under the morning and forenoon illuminations on eighteen occasions, and under the evening on four occasions. Schröter gives a rude figure of it in t. xxiii. --- XI. s. A spot situated on the eastern exterior slope of Plato: it is slightly to the north of eastward of the rock 4, and was seen, on October 14, 1861, moon's age 10:55 days, to be a gently rising protuberance on the eastern slope of the rock, in the neighbourhood of the north-eastern spur. XII. t.—A small crater south of eastward of the rock : it is described, March 22, 9 30 (1861), to be almost due east of the longest diameter of Plato. It is situated on one of the spurs of 4. The rock, the spot s, and the crater t, form a conspicuous triangle, seen to great advantage on March 21, 1861. They have been observed in connexion on three occasions. XIII. A.-The largest crater in the neighbourhood of Plato, figured by Schröter, t. xxiii., and marked c by him, but A by Beer and Mädler. XIV. X-Schröter also gives another crater of about the same size, which he marks x, north of Plato. In his delineation it is placed about midway between Plato and the Mare Frigoris. In the whole course of my observations I have not met with this crater, nor have I seen anything similar to that delineated by Schröter. On the night of August 27, 1861, moon's age 21-53 days, I found a very interesting object on the northern boundary of the bright ground north of Plato. It consisted of a semi-elliptical range of mountains very similar to a half-crater, the existing portion of the ring not greatly elevated above the surface; the south-east side was more elevated than the south-west, so that its external slope caught the rays of the afternoon sun, which rendered it the most brilliant object in the immediate locality. The south-west portion of this half-ring was seen to terminate a little short of the line of junction of the bright ground north of Plato and the dark ground of the Mare Frigoris, the south-east portion being cut off sharply by the south edge of the Mare Frigoris. I did not observe any difference of level between the lighter rugged ground on which the half-ring was seen and the darker and smoother surface of the Mare Frigoris. The situation of this half-ring is very near the locality given by Schröter for the perfect crater. I have indicated it on the key-plan by Schröter's mark x. I also observed this object on September 13, 1861, under the morning illumination, moon's age 8.87 days; and again on September 25, moon's age 21.08 days. It requires the precise angle of illumination and visual ray to catch it. XV. W.-An interesting marking just south of the rock, somewhat of the character of a crater, apparently triangular in its form, but on closely scrutinizing it seen to be a somewhat shallow depression having a gently curved rampart. Under a suitable illumination, the shadow of this rampart has been seen well defined within the enclosure. The south-east rim of this apparent crater, with the contiguous portion of the rim of Plato, forms the continuation of a chain of mountains which takes its rise at an isolated mountain south-east of Plato (c) (see key-plan, fig. 1). This chain of mountains is well seen under the evening illumination about 21.5 days of the moon's age. The position of this depression is on the upper part of the eastern slope of Plato. It is separated from the large crater by a portion of the eastern rim of Plato, which also forms its western rim. On May 2, 1860, the colour of the interior was very slightly, if any, darker than the surface exterior to Plato, and much lighter than the floor of Plato. It has been observed on fifteen occasions. XVI. o. A small crater at the external common base of the rock and the depression W. It has been observed twice. XVII. The south-east rim of the crater Plato. XVIII. c.-A mountain south-east of Plato. The chain of mountains, of low altitude, running from it in a curved direction to Plato formed part of the ring of the ancient crater called Newton by Schröter. It has been observed at least on three occasions. The existence of this mountain is well established, having been observed by Schröter, and marked by him D; by Beer and Mädler, and marked by them c; and by the writer, as above. The chain of mountains is given somewhat differently by each observer, but no doubt can be entertained of its existence. XIX. Y.-A very narrow ledge or terrace within the interior of the southwest border of Plato, appearing as a lucid fringe when the shadow of the summit of the border is sufficiently narrow to allow of the illumination of the floor of the terrace. See fig. 2, in which Section of the south-west interior slope of Plato, the Hartwell Ledge, from observations by W. R. Birt, F.R.A.S. F. Represents the floor of the crater. S-S. The south-west interior slope. S-S. The incident ray when the ledge is in deep shadow, the entire floor being illuminated. S'-S'. The incident ray when the ledge is partly illuminated. On May 18, 70, 1861, I observed the interior shadow of the western rim to fine off on the south-west side. It presented the appearance of a very fine line, with two bright spots, as if there were two small mountains on the ledge or terrace. With Dr. Lee's permission, I propose to designate this terrace the Hartwell Ledge. This ledge has been observed on seven occasions. XX. aa.-The summit of the south-west slope; observed on five occasions. XXI. Z.-A ravine on the surface exterior to Plato ; observed on thirteen occasions. XXII. y. A high peak on the south-west wall, recognized in the early morning illumination by its long shadow stretching far along the floor; observed on six occasions. Schröter has figured the shadow. XXIII. .-A high peak on the west wall, recognized as above, and figured by Schröter; observed on two occasions. XXIV. e.-A similar peak on the north-west wall, also figured by Schröter, and observed twice. These three peaks occasion at sunrise a well-marked indented shadow, which rather rapidly recedes as the sun becomes elevated above their horizon. Beer and Mädler have indicated, measured, and marked them respectively y, d, and e. The shadows have been well seen by the writer on the floor of Plato, with an additional peak. XXV. b.-A dark-black spot in the shadow, most probably the peak 8, which under the early morning illumination would present such an appearance. My observations under the evening illumination have been too few to recognize it as a bright spot, nor have I noticed either y or e as black spots in the morning shadow. This black spot occupies precisely the position of è, just north of the termination of the longer axis of the apparent ellipse exactly opposite the rock . It has been observed on three occasions. XXVI. λ.—A conspicuous mountain south-west of Plato, on the ring of Schröter's Newton, and nearly abutting on the ravine Z (XXI.). Beer and Mädler mark it A, but place it too far to the south-east. It has been observed on nine occasions. Under a very early illumination it may easily be mistaken for a crater (see also XXIX. r). There is a gradual rise of the land from the northwest towards the mountain, which itself rises from a depression, the western cliff of which is very abrupt. XXVII. dd.—A group of mountains in the Alps, forming with λ and an isosceles triangle, λ and being the base. There is a little discrepancy here. The mountain λ has been brought nearer to dd on the key-plan than it would be on Beer and Mädler's map, to give it its proper position with regard to Z, aa, and Y (see XXVI.X). It is the author's intention, as early as convenient, carefully to triangulate the most conspicuous objects near Plato. XXVIII. G.-A small crater, a little to the west of d, somewhat closely abutting on the summit; it is marked G by Beer and Mädler. I have observed it twice. It is very probably the same as w, in Schröter's drawing. XXIX. 7.-A mountain on the exterior western slope of Plato: it is situated in the line of the longer axis of the apparent ellipse. On March 22, 1861, it was seen with the shadow eastward; it had a rounded summit, and the western slope was shining with considerable brilliancy. It has been observed eight times. Its situation with regard to dd and (see key-plan) requires to be determined; also its real character, whether it be a mountain or a crater. On some occasions, under an early illumination, it has been described as a crater; on others, as a mountain. From the description of March 22, 1861, it would appear to be a mountain. It is very conspicuous about the time of full moon as a bright lucid spot. XXX. ee.-A considerable depression east of r, and between it and the western rim of Plato. Observed twice, under a very early illumination of Plato. XXXI. cc.-A somewhat long dark line, in the nature of a shadow with a short spur, apparently the shadow of a mountain across the western wall of Plato; the long dark line observed only once, the spur twice. The exact direction of the line requires determination. XXXII. v.—A conspicuous mountain north-west of Plato, marked by Beer and Mädler; it is figured by Schröter with some smaller mountains and a crater, 4, north-west of it. It was well seen on May 18, 1861; also on July 15, 1861, when two well-marked, distinct rocks were seen north-west of it. It has been observed on seven occasions. XXXIII. ff.-Three mountain-masses (supposed to be v and the mountains north-west of it; they are not given in the key-plan) in the neighbourhood of the mountain v. The westernmost of these mountains not overbright, but the others very bright. XXXIV. gg.-A crater figured by Schröter, and marked by him o, at the western extremity of the three mountains ff. The writer observed and figured it on January 8, 1862; but did not see it on March 8, 1862, when the moon was nearly of the same age. The floor of Plato presents some exceedingly interesting appearances. It is figured by Beer and Mädler as being crossed by four streaks of a somewhat lighter tint than that of the general surface of the floor (see the large Map). These have not been observed within the epochs limiting the period of the observations forming the basis of this Report, January 1860 and May 1862; but a remarkable, broad, branching, whitish, cloud-like streak, erossing the floor at certain epochs of the moon's age perpendicularly, and at others when it is more distinctly apparent in a diagonal direction (f) (see key-plan, fig. 1), has been seen very frequently; in fact, during the continuance of the observations, it may be regarded as having possessed a decided characteristic of constancy. The change of direction of this marking as the sun passes from west to east in his lunar-diurnal course is very interesting, and is in some measure indicative of the nature of the surface of the floor, the direction being apparently dependent on some peculiarity of reflection in the surface. It appears to be connected with the bright mountain (m) on the north-west rim, as under certain angles of illumination it is seen invariably to take its rise therefrom. This is a feature that requires careful watching. It has more than once been traced to the rayed crater Anaxagoras, and on a very favourable occasion was seen to be connected with the ray that terminates near the bright mountain m. It is only visible during certain epochs of illumination. Schröter appears to have observed, in December 1788, a somewhat similar marking, but of a round form (consult his figs. 6, 7 and 8, t. xxi.). Taking the three periods of observation, Schröter's, Beer and Mädler's, and the writer's, it would seem that the markings of the floor are of a variable character. The portion of the floor not covered by this marking, and the whole when it is not visible, undergoes variations of tint, from a decided greenish tint just after sunrise, when it mostly appears with a delicate smooth surface, to a deepblackish grey, of a diluted inky character, at mid-day, the smoothness of surface having considerably disappeared. Beer and Mädler have indicated three or four minute specks on the surface; Gruithuisen detected seven. One, nearly central, I have more or less constantly observed under suitable angles of illumination. The Rev. T. W. Webb has also observed this central speck. It is marked g on the key-plan. Preliminary Report on the Dredging Committee for the Mersey and Dee. By Dr. COLLINGWOOD and Mr. BYERLEY. THIS Committee was appointed last year at Oxford, and the present Report was a résumé of all that had previously, and since then, been ascertained concerning the Marine Fauna of that region. The past season having been very unfavourable for dredging operations, several important families still remained unexplored, chiefly among the minuter Crustacea, Annelids, Entomostraca and Foraminifera. The following comparison of ascertained species with those of the British Fauna will serve to show some of the results given. |