June 1, 1897.] 



KNOWLEDGE. 



143 



sents the eastern margin of the great Mare Imbrium as 

 photographed on October 18th, 1896, at 18 hrs. 32 min. 

 41-47 sees., Greenwich mean time, 2 days 10 hours before 

 the full. 



Some of the photographs taken at Mount Hamilton by 

 Profs. Holden and Colton have been sent to Prof. Weinek 





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Key-ilap to Plate of Aristarclius and Sinus Iriduui. 



at the observatory at Prague, who enlarges them to a 

 scale fully three times as great as that of the Lick atlas, 

 and proposes to issue them in sheets of about nine and a 

 half inches by eleven and a half, as an atlas on the ten- 

 foot scale. Such a magnification is, however, the very 

 outside of that which the negatives will fairly bear — if, 

 indeed, it does not err on the side of excess. Nothing is 

 gained by enlarging a negative to such an extent as to 

 bring into evidence the granulation of the plate, and to 

 render it necessary to hold the picture at much beyond the 

 ordinary visual distance in order to get rid of this disturbing 

 effect. Probably the Lick scale, beside having the advantage 

 of corresponding to a standard map, is In itself more j udicious 

 than Prof. ^Yeinek'3 or that of the Paris atlas. 



The two most striking features of the section of the 

 moon given in our plate, are the brilliant region of 

 Aristarchus and the magnificent bay of the Sinus Iridum, 

 with the noble Highlands which embrace it. 



Aristarchus, as is well known even to the merest tyro in 

 selenography, is the brightest object on the surface of the 

 moon. So bright is it that it is sometimes seen shining 

 like a star, even when the surrounding region is illumi- 

 nated only by earth light when the moon is young. Or 



from time to time — as happened to Captain Noble on 

 August 15th, 1883 — the moon maybe absolutely blotted 

 out to the observer by mist or passing cloud, and yet 

 this remarkable formation continues to "shine like a 

 small iU-defiued planet." 



The formation is not a large one, as it is a ring-plain of 

 only twenty-nine miles in diameter, and its wall rises but 

 some two thousand feet above the surrounding surface. 

 The interior is deep — how deep it is difficult to say, the 

 measures of different observers being by no means accor- 

 dant ; but it would appear to be some three or four thousand 

 feet below the level of the outer surface. The central 

 mountain is of quite insignificant height, but forms the 

 most brilliant point of all this bright region— the floor 

 being only slightly less bright, and the north and east 

 wall coming next in the order of brilliancy. 



The extreme brightness of this object renders the study 

 of its details a matter of some difficulty, and, as will be 

 seen in the photograph, it is decidedly over-exposed. The 

 very remarkable terracing and series of buttresses which 

 it possesses, particularly towards the south, escape notice 

 on the photograph, partly from this reason, and partly 

 from the character of the illumination at the time the 

 photograph was taken. But another remarkable feature 

 is quite obvious — that is to say, the great system of rays or 

 bright streaks, which radiate from Aristarchus as they do 

 from Tycho to a very much greater extent. Still, Aristar- 

 chus may claim to be one of the seven great ray centres, 

 though far from being the chief. Two others, Copernicus 

 and Kepler, lie just outside our plate to the south, and 

 their rays may be noted as entering our photograph, and, 

 in some instances, becoming confused with the Aristarchus 

 rays. Euler, a minor ray centre, is included in the plate. 



Herodotus, the companion of Aristarchus, is far less 

 bright ; the floor, in particular, being very dusky. The 

 most interesting feature of the formation, the great serpen- 

 tine cleft, is admirably shown on our photograph, especially 

 the point where it turns south, and defines the eastern 

 boundary of the high plateau of Aristarchus. This latter 

 region is one of great complexity, and still offers a wide 

 field for the close student of selenographic detail. 



Turning northward from this interesting region, which 

 we might almost call the lunar " Albion," and passing the 

 pretty little group of the Harbinger Mountains — which do 

 not, however, possess any features sufficiently striking to 

 detain us now — we reach the small ring-plain, Gruithuisen. 

 One of the dependencies of this latter is a high, flat, isolated 

 plateau (well seen on the photosraph), which forms the 

 introduction to the noble Iris Highlands, the wild and 

 lofty character of which the plate distinctly indicates. 

 These Highlands form a portion of that great mountain 

 region which runs right round the north of the moon, 

 bordering the two great seas of Serenity and of Rains, until 

 it ends in Mount Arga-us. Of this great mountain system 

 the Iris Highlands form the loftiest and most intricate 

 region, and, in particular, between Mairan and Sharp we 

 find its wildest portions, the highest peaks of which rival 

 the giants of the terrestrial Alps or Caucasus. 



The great feature of these highlands is the magnificent 

 ba.y which they so nearly enclose, and from which they 

 take their name. The Sinus Iridum is some hundred 

 and thirty-five miles across, between the two horns of the 

 bow, and the sagitta is eighty-four miles. The area, 

 therefore, of the bay is double that; of Wales, including 

 ^lonmouthshire. The splendid sweep of the cliffs — almost 

 a true semicircle, and rising in certain peaks to the height 

 of Mont Blanc— stand out in such contrast to the dark 

 level surface of the Sinus that it seems impossible to escape 

 the suggestion that we have here a veritable coast-line, 



