86 



♦ KNOWLEDGE ♦ 



[Aug. 10, lf<83. 



But there is a pretty way of testing the depression of 

 the water horizon due to terrestrial rotundity, which 

 requires no telescope, and only a little care in execution. 

 Parallax used the method, in a purposely inexact way to 

 show the earth to be flat. 



This method will be considered in our next. 



(To be continued.) 



THE MOON IN A THREE-INCH 

 TELESCOPE. 



By a Fellow of the Royal Astroxomical Society. 



"XTTHEN the Moon is nine or ten days old, the Bay of 

 * \ Rainbows (P in our map) presents a perfectly 

 charming spectacle to the observer. This great, dark, semi- 

 circular area appears absolutely level in the instrument we 

 are using, but is surrounded by a mass of stupendous cliffs. 

 It measures, from Cape La Place (134) to Cape Heraolides 

 (135), nearly 135 miles. Heraclides rises some 4,000 feet 

 above the level of the bay, but is as a mere hillock com- 

 pared with some of the neighbouring highlands. As we 

 travel in an easterly direction we arrive at Sharp (139), 

 15,000 feet in height, and some of the peaks in this chain 

 probably attain an altitude approaching to 20,000 feet. 

 Nearly due south of Cape La Place lie two little, but exceed- 

 ingly deep craters — the Eastern one of which. Helicon, is 

 marked 129 in the map. And now we arrive at a region 

 covered with systems of light streaks, akin to those de- 

 scribed on p. 56 as emanating from Tycho. Euler (125), 

 a fine ring plain, 19 miles in diameter, \vith a central peak, 

 is the centre of one of these systems of rays. Tobias 

 Mayer (117), 22 miles across, is an interesting object 

 under suitable illumination. Of all the formations, 

 however, in this region of the Lunar surface, there is 

 nothing to compare with that superb one, Copernicus (112), 



:^ 



Copernicus. Moon's Age, 10'27 days. 



our sketch of which above was taken with a power of 

 160, when the moon's age was 1027 days. This magnifi- 

 cent ring-plain measures 5G miles across. There are, alto- 

 gether, eight peaks rising from the interior — three bright 

 ones, and four less so. With the instrument employed, 

 however, and under the conditions of illumination then 

 obtaining, two only of these were, as will be seen, visible 

 at the epoch of our drawing. The terraced character of the 

 wall is conspicuous enough, even in a 3-in. telescope, as is the 

 disturbed and complicated character of the region imme- 

 diately surrounding it. Two deep craters south of 

 Copernicus, approximating in appearance to the figure 8, 

 will at once strike the eye. So also will a conspicuous 

 peak on the western wall, which is between 11,000 and 



12,000 ft. high. The somewhat angular character of the 

 contour of the wall is well seen from the shadows cast 

 towards the east. Other features will strike the attentive 

 observer. At full moon, Copernicus is seen to be the 

 centre of a system of light streaks, uniting with similar ones 

 from other formations, to which we shall hereafter refer. 

 It is worthy of note that the streaks extending in a 

 westerly direction from Copernicus are the most numerous ; 

 though those which lie towards the north are individually 

 more conspicuous. There is an enormous number of tiny 

 craters between Copernicus and Eratosthenes (110) ; but 

 even the largest of these require favourable illumination and 

 conditions, to be seen in our instrument. Reinhold (114), 

 31 miles across, will repay scrutiny while the telescope 

 is turned on this part of the moon's visible disc. Euclid 

 (221), and Landsberg (222), furnish examples of craters 

 surrounded by a kind of nimbus or light ring. This, as 

 will be seen on examination, difl'erg in appearance from the 

 streaks emanating from Tycho, CopCTnicus, Kepler, and Aris- 

 tarchus. Kepler (144), by the way, may be here referred to 

 as a crater, close upon 22 miles across, the centre of a great 

 system of light streaks, uniting with those from Copernicus. 

 Close to Euclid lie the Riphrean Mountains (220). Under 

 oblique illumination they strongly suggest an exaggerated, 

 or caricatured, bas-relief of a Uama or giraffe. One of the 

 deepest craters in the Sea of Clouds is Bullialdus (213), 

 to which a light sti'eak extends (as mentioned on page 56) 

 from Tycho (180). This is 38^ miles across, with finely- 

 terraced walls of considerable breadth, and a fine central 

 mountain 3,000 feet high. The considerable crater or ring- 

 plain, breaking into the southern wall, too, will at once 

 strike the eye, while a very similar one (but detached from 

 Bullialdus proper) will be noted to the south of this again. 

 Campanus (226), a ring 30i miles across, in this neighbour- 

 hood, is chiefly remarkable for the darkness of its interior. 

 Hainzel (237) is a kind of pear-shaped ring-plain, 55 miles 

 in its longest diameter, with high and precipitous walls 

 rising some 11,600 ft. in places. The wall of Capuanus 

 (238), too, will repay examination under suitable illumina- 

 tion. Capuanus is one of the comparatively few craters 

 that remain conspicuous and identifiable when the Moon is 

 full. We are now in the neighbourhood of the Sea of 

 Moisture (T in our map). The student may begin his ex- 

 amination of this region with the large bay in this " sea," 

 Hippalus (225). The chief interest, however, attaching to 

 this locality resides in the wonderful system of " rills," or 

 narrow and tortuous clefts, existing to the west of Hippalus. 

 The majority of these require a large instrument for their 

 detection, but one or two of them are within the reach of a 

 three-inch telescope when the Moon is between nine and 

 ten days old. The formation of ViteUo (229) .=eems to 

 afford an illustration of the vulgar phrase, "a wheel within 

 a wheel," inasmuch as the outer ring-plain encloses another 

 one, from the interior of which rises a mountain, 1,600 ft. 

 or 1,700ft. high. With the examination of Gassendi (232), 

 on the northern boundary of the Sea of Moisture, we shall 

 conclude another night's work. 



Our sketch of this fine and interesting formation was 

 made with a power of 160, the moon being 11 -24 days old, 

 and Gassendi very nearly on the terminator. The diameter 

 of this great walled plain is fifty-five mUes. The height of 

 its surrounding cliffs varies greatly ; in places they rise 

 to an altitude of some 10,000 feet, while towards the 

 south, as will be seen in the drawing we give, they diminish 

 to a twentieth part of that height. It is worthy of remark 

 that Madler asserts that the floor of Gassendi is in its 

 northern part quite 2,000 feet above the level of the almost 

 adjoining Sea of iloisture. It will be observed how the 

 northern part of the wall has been destroyed by the s-ubse- 



