376 



KNOWLEDGE 



[Mabch 3, 1882. 



NIGHTS WITH A THREE-INCH 

 TELESCOPE. 



Uv "A F.-:i,i,(iw OK Tin: Hoval Asthokomical Sociktv." 



OUR first oliji'ct to-night shall lie that bnautifui aiici 

 familiar doiilile-star « Ciominoruiii, or Castor (Map, 

 p. 298). This, with tho instruriiont wo aro oniploying, we 

 shall (iiul to Ix- a pei-fcctly pasy olijcct ; in fact, wore th<' 

 young oliscrviT furnished with the means of accurately 

 directing his telescope, Castor nn'ght lie seen double in hriglit 

 twilight — or even in liroad daylight. Its telescopic a.spect, 

 with a power of TJO, is shown in Fig. 20. 



Fig> M. — Castor. 



Geminorum is another star which will repay examina- 

 tion. It will be found in the Map on p. 298. The small, 

 purplish companion will be found abo\ c the principal star, 

 and just to the left of the lower circle passing through it 

 1. (below Pollux in the same map) is a ditticult and delicate 

 pair, requiring a tirst-class instrument and acute vision to 

 see the comes at all. 38 in this constellation (bottom square 

 but one in the left-hand corner of Zodiacal Map, p. 225), 

 though ditHcult, is a decidedly easier ol)jectthan ».•. In both 

 these stars the contrasted colours of the companions are 

 very fine. Many other oljjects will be found marked D and 

 B in the map ; but, being invisible to the naked eye, they 

 are by no means easy to pick uj) without an equatorial 

 mounting. 



Cancri is not a constellation containing man}- objects of 

 interest witliin the power of a three-inch telescope. Never- 

 theless the studwit will see ^ as a double star (it is really 

 triple), ifi" is another object, approximately as easy to see 

 as <f. 66 Cancri is decidedly more difficult ; for, although 

 the components are about the same distance apart as those 

 of (p-, their considerable inequality makes the comes look 

 small by contrast. Fig. 21 exhibits it as seen when best 

 defined with a power of 1 60. 



Kiir. 21.— CG Ciiiu-ri. 



I Cancri is chiefly interesting from the contrasted colours 

 of its components. They are, relatively, very wide apart 

 Sliould the observer possess a day eye-piece, he may put it 

 on to scrutinise the Pne.sepe witli. At all events, he must 

 use the lowest power he has. The same eye-piece may be 

 retained to look at another cluster, 67 Messier, somewhat 

 to the west, or right, of ci in the sky. 



And now wp arrive at a star which, while scarcely 

 affording a crucial test, yet requires a very good eye and 

 instrument to se<' it well and cleanly separated. We refer 

 to the familiar one, y Leonis (Ma|>. p. 298), which, with a 

 power of 100. should present the appearance indicated in 

 Fi-. 22. 



A more diflicult object, and one which will severely tax 

 till- powers, both optical and visual, of the observer, is 

 1 Ijeonis (Map, p. 298). r»4 I^eonis is a charming object 

 There are a very great many small pairs in Leo ; but the 

 remarks which we have made al>ove in connection with 

 t<;lescopic .stars in Gemini are equally applicable here. If 

 the .student will fish about the apex of an equilateral 

 triangle, whereof a and y lyonis form the (jxtremities of 

 the base (to the left, or ea.st, of the line joining them) with 

 the lowest power at his dis]iosaI, he will find himself in a 

 region rich in nebula;. 



y Leonis. 



Underneath Leo in the maps will be found the foolish 

 modern constellation of the Sextant 35 Sextantis is 

 worth looking at, as a curious disagreement exists as to 

 the colour of the comes. There is a bright nebula, too, 

 worth examination, in Sextan.s. It is 163 of Sir William 

 lierschel's 1st Catalogue. 



Hydra, straggling across the sky beneath Cancer, Sex- 

 tans, Crater, Corvus, Virgo, and Libra contains a consider- 

 able number of interesting objects, though but few of them 

 are susceptible of exsy recognition, e Hydra- is a fine pair, 

 but difficult with such an instrument as we are employing, 

 on account of the proximity of its components, and of their 

 disparity in size. Of the objects in Crater and Cor\-us 

 (two figures perched by the map-makers on Hydra's back), 

 we need here only allude to 17 Crateris, an easy double 

 star, wnth prettily-contrasted colours ; and to c Corvi, wider 

 apart still, but exhibiting even more prominent tints in its 

 components. About three-quarters of the way upon an 

 imaginary line drawn from <i to e Corvi will be found a 

 nebula, 65 of Sir William Herschel's 1st Catalogue. By 

 this time, the incipient astronomer will probably feel that 

 he has accomplished a fairly good night's work. Our 

 next night we shall devote to Virgo and the neighbour- 

 ing region of the sky. 



A SPINNING-TOP. 



IN an American paper, the Literary Jficrocosm, the 

 following questions are asked : — 



1. Why does a rapidly spinning-top, when tilted, tend to 

 swsume an upright position t 



2. W'hy does it swing bodily and slowly around its pivot t 



3. Why does this bodily motion take the direction of 

 that part of the revolving surface of the leaning top which 

 is nearest to the ground 1 And 



4. Why does this bodily movement of the top become 

 faster as its rotatory movement becomes slower ! 



These questions are worth careful study. The Literary 

 Microcosm gives an utterly unscientific answer, based on 

 the absurd conception that force is matter, and somehow 

 explaining at the same time the rotation of a top and the 

 duality of man ; but the questions are really of interest, 

 especially the first. We leave them to our readers, noting 

 that a number of interesting experiments may be made by 

 modifying the shape of the rotating lx)dy, and the manner 

 of its rotation. One of these we have described in No. 11, 

 p. 219. The Editok. 



