April 1, 1901.1 



KNOWLEDGE. 



R.' 



Palus Nebuliinim. The first is seen as a iMther shallow 

 de|iressiou, str-tchinLr from Archimedes south-west to the 

 Aj>euniues, aiul out off from the rest of ihe sea l\v the hii;h 

 ruartred iiri^iuJ that seems to hive overflow**!) from Arelii- 

 niedes on the south, and bv the "aureoles" of Autolvcus 

 on the north. Tlie Pahis .V'etmlarum lies north of Avis- 

 tillus, jind is bounded bv the ridges which conuect tha'' 

 great riuire'l pla.n with Autolvcus on the south and with 

 Cassini on the noith. 



The Sea oT Cold is too mneh £oreshortf»ned for the 

 detail on its floor to be elearlv made out. It would seem 

 to resemble the Sea of Serenity rather tbau the Sea of 

 Kain. and the position of Eirede A on its intersecting- 

 nd^es eertainlv seems to recall the position of Bessel. 



J>istant as Aut'ilycus, Aristillus and (\assini are from 

 the Caucasus mountains, they yet seem to have exercised 

 some local iuflu-'Uce on them. MJI. Loewy and Puis'ux 

 point out that if lines are drawn jiarallel to that from 

 Autolycus tbroui^rh the ereat pass, through the centres of 

 Aiistillus Theaeletus, Cassiui and Eudoxes, these lines 

 ■will all lie alonpf depr»-ssions in the mountain range. 

 Another feature that they point out is the deep depres- 

 sion that occurs at the ■ utside base of the craters 

 and of the mountain ranges. This is well seen round 

 Archimedes, along the base of the Alps west from Plato, 

 both on the north side and on the south, and most 

 markedly on the eastern side of the Caucasus where it 

 crosses the Alps, and distinctlv, though less markedly, on 

 the western side. These two depressions in tlie meridian 

 line crossing the five depressions which pass through the 

 great craters of the Sea of Rain, and through Eudoxes, 

 divide up the Caucasus range into four great rectangles, 

 and the mountains north of Eudoxes are so divided from 

 the rest of the range that they appear but as isolated 

 peaks. 



The two most important and most beautiful ringed 

 plains shown on the photograph are those of Archimedes 

 and Plato. Of nearly eaual size, both have the same 

 regular almost unbroken rampart, both have their interior 

 plains but slightly depressed, but the floor of Archimedes 

 is brilliant, and the curious dark bands as it crosses the 

 meridian at right angles are easily seen. The floor of 

 Plato, on the other hand, is very dark, and no detail can 

 be made out in this photograph. MM. Lo^wy aud 

 Puiseux attribute the bands on the floor of Archimedes 

 to the influence of the two large adjacent craters, some 

 pointing towards Aristillus at-d some to Autolycus. 

 Plato, the " Black Lake," as Hevelins called it, is the best 

 example of those plains which become relatively darker as 

 the age of the moon increases. 



CONSTELLATION STUDIES. 



By E. Walter Maunder, f.r.a.s. 



IV.— BOOTES AND HERCTLES. 



Theee bright stars ride the northern heavens, three stars 

 so equal in magnitude that our highest authorities differ 

 as to the order in which they should be classed in bright- 

 ness. All three are above the horizon in the April 

 midnight, but whereas Yegaand Capella are couiparatively 

 low down in the east and west respectively, Arcturus is 

 now approaching the meridian. 



Arcturus is one of the easiest stars to recognise in the 

 entire sky. If w-j start from the Pole Star, we find that 

 the last star in the Plough Handle is just halfway to 

 Arcturus ; or the curve of the three stars of th : handle of 

 the Plough, if continued, seems to bring us round to the 

 same place ; or reverting to our two last studies, Denebola 

 of Leo and Spica of Virgo and Arcturus mark out a 

 triangle, almost equilateral. 



The star owes its nunc to its nearness to the Bear. 

 It is Arcturus. the " Watch' r of the Bear." It is now the 

 brightest star in the constellation Bootes, the Herdsman, 

 but in the catalogue of Ptolemy it is not includi'd in the 

 actual figure, but is an "unformed" star belo«' him. 

 There seems to have been some reason for ihi.s exclusion, 

 for Theou and Hesychius call Bootes, Orion, and when 

 Arcturus is excluded, the principal remaining stars of the 

 constellation m ike up a representation, pal" and distorted 

 it is true, but a representation for all that of the most 

 glorious constellation of the sky. This circumstance may 

 explain an allusion iu Isaiah xtll. 10, widch has puzzled 

 many commentators, " The stars of heaven and the 

 constellations ther. of." The word "constellations" is in 

 the pluralf and is the same word \diich is in the s ngular 

 in Job IX. 9, .'ob xxxvtii 31. and Amos v. 8; and 

 which is iu each case translated with great probal)ility 

 "Orion." Here then it may stand for the two Orious, 

 Bootes being one. However this may lie, the resemblance 

 between the two constellations will be near enough to help 

 the student to trace out the figure. Arcturus stands 

 nearly midway between the Herdsman's two legs, marked 

 respectively by the stars Ela aud Zeta ; above Arcturus 

 are the three belt .stars, Hho, Sigma, aud Epsilou, I'ipsilon 

 being much the brightest. Above we find (iamma and 

 Delta marking the shoulders, whilst Beta takes the place 

 of the cluster of small stars which denotes the head of 

 Orion. 



Arcturus and Gamnia form two points of an equilateral 

 triangle with K|)silou in the centre; the third point is 

 formed by Alphecca, the Hroken Platter. The reason of 

 the name is readily seen, since right and left of Alphecca 

 are four other stars, two on each side, making up a semi- 

 circle, and suggesting to the old Atabiau star-gazers a 

 broken plate held out by a beggar to receive alms. This 

 very sordid title contrasts poorly with its classical name, 



" That Crown which I >ionyso3 placet! 

 Of Ariiidne dead, a glorious sign." 



The constellation though so small is, from its shape and 

 its nearness to Arcturus, very easy to find. Or the old 

 rhyme may guide us if we turu back to Virgo, aud pick 

 out Epsilou, the " Herald of the Vintage." 



" From Epsilon iu Virgo's side, Arctie-us seek and stem, 

 And just a- far again you'll spy Corona's beauteous gem ; 

 There no mistake can well befall e'en him who little knows. 

 For bright and circular, tlic Crown conspicuously glows." 

 The small size and neat arrangement of Corona make it 

 a pretty object for the opera-glass; aud in 1866 it afforded 

 a grand chance for the naked-eye observer. For on the 

 night of May 12th. in that year, the cimstellatiou siiddeidy 

 presented an uu wonted shape. E[isilou, the star of the 

 five furthest to the east, was overshadowed by a new aud 

 bright companion which outshone Alphecca. This was 

 T Corouae, the first "new star" to appear since the 

 invention of the spectroscope. Less brilliant than the 

 new star in Perseus which has so suddenly blazed out 

 upon us, it created, as the first example of the kind that 

 had occurred in the new era of astronomy, an even greater 

 sensation ; and the discovery in its spectrum of the bright 

 lines of hydrogen aroused the utmost interest. Six nova- 

 have appeared since the date of T Coronae. including the 

 one so recently discovered by Dr. Ander.son. So far, 

 however, as the relatively incomplete observations of its 

 spectrum changes go, they seem to point to T Corona 

 being a nova of a different order from those which have 

 succeeded it. 



A line from Gamnia Bootis through Theta Coronae, the 

 most westerly of the five stars of the " Broken Platter." 

 brings us, at an equal distance beyond, to Beta in tlie 

 constellation of the Kneeler. This is not -i luilliuit 



