SEPTIi>r8tB, 1901.1 



KNOWLEDGE. 



201 



mount-ainous district, to the uorth, tlirough the plain, 

 ;uid along the lloor on the base of the eastern rajnpart 

 of P.u•l•^•. and skirting the eastern tlank of the orater 

 Parry A. 



Tliere ai'e several of these vcrv delicate rills seen on 

 the photograph. They usually appear cleaving the tloor 

 of one of the ancient walled plains. One still finer than 

 that crossing Fra Mauro, traverses Letronne from north 

 to south, and seems to end in the highland country 

 lying between Letronne and Gassendi. Another and 

 verv remarkable one, not mentJoned by Neison, cuts 

 Gassendi itself right across from east to west. It seems 

 to mai-k the limit which the Mare Huniorum would 

 have reached had not the ramparts of Gassendi been 

 already there, and it is a continuation as a rill of the 

 mountain ridije that fomis the eastern border of the 

 Mare, and that joins the rampart of Gassendi 

 immediately to the south of the triangular ridge, 

 Gassendi H. This eastern border of the Mare Hiunoinim 



Heinsius (^1 



ainiiryV) 



J{ *Clausius 



GauricosV.^ yj>cLl^l,(S) C® \i^ '5Ramsden 



^ ^ Cichus 





Key Map of Plate. 



is itself a remarkable object. It is evidently comple- 

 mentary to the three deep parallel clefts on the western 

 banks of the sea, but in its northern part it is decidedly 

 a ridge ; in its southern, where it passes through 

 Doppelmayer g, its nature is doubtful, for Neison calls 

 it a '■ rill " there, and Loewy and Puiseux term it a 

 ■' terrasse." 



About half-way between Bullialdus and Guerikc, and 

 slightly inclined to the meridian, is seen a chain of 

 three or more ringed plains far advanced in ruin. At 

 least the photograph presents them almost unmistak- 

 ably as ringed plains, but Neison in his " Moon ' 

 figures only the most northern member of the chain as 

 such, not perceiving the western or separating walls of 

 the more southern. At the north-east and south-west 

 corners of the central plain, where it cuts the cuter 

 members of the chain, are two craters of comparatively 



recent origin, and a straight rill unites the two and is 

 tangential to their north-western Hanks. We seem here 

 to see the cause of the ruin and semi-obliteration of 

 the ringed plains in tiie conjunction of rill and crater, 

 both signs of weakness in the lunar crust, and causing 

 subsidence on one side and upheaval on another. 



Due east of the triplet of walled plains. Fra Mauro, 

 Parry and Bonpland, and about half-way between "them 

 and Wichniann, lies a curved and continuous range of 

 hills, the Riphaen Mountains. The ciuve of these hills 

 appears on the photograph to be continued towards the 

 west and then round to the .south by a scries of isolated 

 peaks, and the central lloor is smooth and unbroken 

 save for a pair of very small craters, so that the 

 impression is given that here we have the remnants of 

 a huge walled plain, many times larger than Gassendi, 

 whose ramparts are still intact on the east, much broken 

 towards the north and west, and entirely submerged 

 towards the south. 



Still another instance the photograph seems to give 

 of a walled plain that has now become not only partially 

 but entirely submerged. To the south-east of the 

 Riphaen Mountains are two craters, llerigonius B and 

 C ; and round C, the more southern of these, is seen a 

 broad circular dark marking that looks like the wall of 

 an ancient plain that has been not only levelled, but 

 even depiessed below the surrounding surface by the 

 action of the great central volcano. 



The most perfect and stable in appearance of all the 

 walled plains seen on the photograph is Gassendi. Tlie 

 north-east corner shows a marking on the floor which 

 forms a curious copy of the shape of Ga.ssendi itself 

 with its gi-eat parasite ringed plain, Gassendi A, hang- 

 ing on its northern border. 



Two other curious markings ai-e seen, triangular in 

 shape. One is the deep right-angled triangle that, is 

 stamped on the northern spur of the Riphaen 

 Mountains, the other is a deep triangular impression in 

 the mountainous region to the south of Cichus A. 



THE GREAT SOUTHERN COMET (1901 I). 



By W. F. Denning, k.r.a.s. 

 The brilliant comet vifhich suddenly appeared in the 

 morning sky on AjDi-il 24 incited widespi'ead obsci-vation 

 and comment from southern observers. The merit 

 attaching to its first discovery apparently rests with 

 Mr. Arthur Hills, of Queenstown. The object, apart 

 from its conspicuous and almost startling aspect, formed 

 a view, veiy picturesque of its kind, in the Iwilr^'ht ovta- 

 the eastern horizon. It exhibited a short, brilliant and 

 almost vertical tail with a dark rift running lengthwise 

 along its central part, and during May there was a long 

 filmy streamer, or faint secondary tail, directed to the 

 south and inclined at an angle of about 35° to the 

 brighter tail. Major Eddie, who obtained some 

 magnificent views of the comet at Naauwpoort, S. Africa, 

 says that on May 6 " the bright straight tail with its 

 faint extension was about 16° long, reaching nearly to 

 Rigel, while the enormous lateral emission of shimmer- 

 ing light flooded the S.W. sky with a ghostly gleam 40° 

 long, 6° to 10° broad ; while the whole space between 

 this mighty extension and the more brilliant tail was 

 filled with a gauze-like sheen." (/i. A. A. Journtil, 

 June, 1901.) 



Several of the observers may bo said to have dis- 

 covered the comet for themselves, for they had no 

 intimation of the presence of the brilliant visitor until 

 they saw it shining in the sky. When it was first 



