KNOWLEDGE • 



[April 13, 1883 



reduction; and it is remarkable tliat, altliough the Post- 

 iiiastcT-General, and other members who liave in previous 

 years held his appointment, voted against Dr. Cameron's 

 "motion, they all spoke in terms which must have been 

 hij;hly gratifying to tliose anxious for the reduction. It 

 is possible for tins wires to carry much more traflSc than is 

 at present demanded of them. Of the G.")3* circuits, only 

 190 are duplex, 54 Wheatstone automatic, and 12 quadru- 

 plex. The remainder comprise 148 single needle, 1 

 Hrll, 4 Wheatstone A. B. C, and 244 single-working Morse 

 printer and sounder circuits. The latter group are 

 all capable of being converted into duplex or Wheatstone 

 circuits, and not a few into quadruplex circuits. The 

 great difficulty, therefore, so far as the central office, and 

 offices in connection with it are concerned, is not the want 

 of wires, but of accommodation for apparatus, demanding 

 larger space than is at present available, and, having secured 

 that, tli<; creation of an army of trained telegraph clerks to 

 work the circuits. The latter requisite is no small item ; 

 and those who once boasted they could take a boy from 

 the plough-tail and transform him into a telegraphist 

 within three months, would have cause to be grateful if 

 they could accomplish such a transformation upon youths 

 of average intelligence in four times that period. 



It is noteworthy that several experiments have been 

 made to test the adaptability of the electric light The 

 office is at present illuminated by gas consumed at 476 

 burners, the heat and the deleterious products resulting 

 from so large a consumption being, as may be imagined, 

 very troublesome. It is gratifying, therefore, to learn that 

 the old illuniinant is likely to be replaced by Edison in- 

 candescent electric lamps, 1,500 of which, as we noticed 

 recently, are (it is said) to be fixed in the various parts of 

 the building. 



THE MOON IN A THREE-INCH 

 TELESCOPE. 



By a Fellow of the Royal Astronomical Society. 



■\T7E have now taken the student through the whole 

 VV twenty -four hours of right ascension of our 

 visible stellar vault, and have incidentally given sketches 

 and descriptions of such planets as happened to be situated 

 in those parts of the sky which we were engaged in 

 describing at the time. So far, however, we have said 

 nothing of the moon, and we therefore propose to treat of 

 her in somewhat more detail, as, probably, one of the first 

 objects to which the incipient possessor of a telescope will 

 be likely to direct his instrument and attention. But we 

 are not going to write here a complete treatise on seleno- 

 graphy. Those of our readers whom we may succeed in 

 interesting sufficiently in this subject will, doubtless, pro- 

 ceed to the section devoted to it in Webb's admirable work, 

 " Celestial Objects for Common Telescopes," and to that 

 even more elaborate one, "The Moon," by Mr. E. Neison, 

 which may be fairly regarded as a kind of lunar encyclo- 

 piedia. What we propose to do in these papers is to point out 

 to the possessor of a 3-in. telescope exactly what it may be 

 expected to show him in the shape of lunar scenery, and 

 of the general physical conformation of our satellite. To 

 this end we here present a map of the moon, founded on 

 the excellent one by Mr. Webb, and which also appears in 

 the volume on " The Moon," by the Editor of this journal. 

 We have purposely retained the lettering and numbering 



• This total includes 17 circuits at tlio Stock Exchange Office, 

 which is regarded as part of the central station, and through which 

 l,720,l:;l telegrams passed in the year 1881-2. 



adopted by Mr. Webb to facilitate reference, and propose 

 to describe and draw a selection of the oVyects thus indi- 

 cated, with the end of familiarising the student with the 

 principal features of the surface of our satellite. Some of 

 the chief of these we shall draw at the telescope, in order 

 that the young observer may know precisely what to 

 look for ; and we shall in all cases give the exact 

 age of the moon and the powi-r employed, in order that 

 our sketches may be directly comparable with the moon 

 herself. The map almost explains itself. It gives an in- 

 verted image of the moon as it would appear in a telescope 

 with an ordinary Huyghenian eye-piece of low power. The 

 curved lines represent the lines of lunar longitude, the 

 moon being supposed to be in what is called her condition 

 of " Mean Libration." The meaning of this phrase (which 

 is, however, not very material for our present purpose) will 

 be found thoroughly explained in the work on " The Moon," 

 by the Editor of Knowledge, to which we have referred 

 above. One immediate use to which we may put these 

 lines is this. The curve separating the illuminated part of 

 the moon's disc from the dark part (technically called the 

 "terminator") creeps over her face at the rate of 12° 1' 

 26 7" per diem. Hence, when she is one day old, the 

 central part of this arc will be in lunar longitude 79° 49' 

 33-3" east of her centre ; at two days old, at longitude 67° 37' 

 6-6" east ; and so on until she is 7'38 days old, when she will 

 be "dichotomized,"orexactlyhalf light and half dark. So far 

 the bright crescent is concave towards the east. Afterwards 

 the moon has entered her " first quarter," the " termina- 

 tor " becomes convex towards the east, and continues to 

 increase in convexity until full moon, when it merges in 

 the moon's general circular outline. Suppose, now, that 

 the student wishes to know what formations are near to 

 the boundary of light and darkness when the moon is 

 5 days old. 5 x 12° 11' 26-7"=60° 67' 13-.5", the longitude 

 of the terminator from the west limb. Taking this from 

 90°, we find 29° 2' 46-5" as its longitude from the moon's 

 centre ; and now, looking at the map, we see that when 

 the craters and ring plains 374, 371, 372, 323, 57, 48, 37, 

 itc, will all be illuminated (albeit, very obliquely), the sun 

 will not yet have risen on 367, 321, 320, 319, 318, 47 and 

 50, and only partially on 54. In like manner, the position 

 of the terminator at any other age of the moon may be 

 determined. 



In fact, our chief object in introducing these lines of 

 longitude at all is to supply the beginner with the means 

 of ascertaining, with suliicient accuracy, when any given 

 formation is most favourably placed for observation, and, 

 incidentally of identifying it. AVhen once he is familiar 

 with the leading features of the lunar surface, he will 

 easily be able to determine for himself the times at which 

 they can be most advantageously examined. If we reflect 

 for a little, it will be seen that this must evidently be 

 when the object under examination is most obliquely 

 illuminated — in other words, when it is tolerably near to 

 the boundary line between light and darkness. Suppose 

 that we had to determine the shape of a white basin 

 at a distance of a couple of miles, with a pocket tele- 

 scope, at night, and had our choice as to the method 

 of illuminating it. Obviously we should not cast the 

 light of a lantern directly into it — or we should 

 perceive nothing but a circular white patch in the telescope. 

 We should light it from the side ; the shadows which it 

 would in consequence cast revealing its contour distinctly. 

 Now, at full moon the sun is (for our present purpose) 

 shining vertically on to our satellite, which, consequently, 

 presents nothing but a mottled, spotted, and shaded sur- 

 face, the most conspicuous features being certain dark 

 patches, erroneously named "seas," and a radiating series 



