188 ' REPORT — 1861. 



XXXIV. gg.—A crater figured by Schroter, and marked by him ^, at tlie 

 western extremity of the three mountains //. The writer observed and 

 figured it on January 8, 1862; but did not see it on March S, 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 Madler as being crossed by four streaks of a some- 

 what 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 tiie observations forming the basis of this Report, January 1860 and May 

 1862 ; but a remarkable, broad, branching, whitish, cloud-like streak, crossing 

 the floor at certain epochs of the moon's age perpendicularly, and at others 

 when it is more distinctly apparent in a diagonal direction (/) (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 coustunci/. 



The change of direction of this marking as the sun passes from west to 

 cast 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 witli tlie ray that terminates 

 near the bright mountain m. It is only visible during certain, epochs of 

 illumination. 



Schroter 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, Schroter's, Beer and Miidler's, and the writer's, 

 it would seem tliat 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 deep- 

 blackish grey, of a diluted inky character, at mid-day, the smoothness of sur- 

 face having considerably disappeared. 



Beer and Miidler have indicated three or four minute specks on the sur- 

 face ; Gruithuisen detected seven. One, nearly central, I have more or less 

 constantly observed under suitable angles of illumination. Tiie 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 resume 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, Ento- 

 mostraca and Foraminifera. The following comparison of ascertained 

 species with those of the British Fauna will serve to show some of the 

 results given. 



