220 



KNOWLEDGE 



[Jan. 13, 1882. 



reeling can lip quite easily made. A convenient way is to 

 have a f;lol)e of iron hollowed out, as in Fig. 2, and set in 

 rnpiil rotation— which may most conveniently he done l>y 

 having a projectinj;; rod at the top, pierced to receive a 

 string, as /Ij, and pointed, so that a metal plate, as JIN, 

 with a hollow to receive the end of axis /), may he held 

 against it while the wound-up string is sharply drawn off. 

 The heavier the globe the steadier will its motion be found 

 to be, the slower and the more constant its reeling. 



Tiiere is, however, a morn perfect method of illustrating 

 the precession of the equinoxes or the earth's rerJinr/, and 

 also the nutation (or nodding, still to be described), in the 

 instrument invented by my esteemed friend, the late Mr. 

 Burr, of the Astronomical Society. This instrument I will 

 sketch later. 



NIGHTS WITH A 3-INCH TELESCOPE. 



PRESUMING the reader to be now in possession of 

 such a telescope as that described in our first article, 

 and that he has placed it on a tirm stand of convenient 

 lieiglit, with the bar, BM, as nearly as practicable in the 

 meridian, we will begin our examination of the heavens 

 by turning towards the western and south-western sky, 

 inasmuch as th(! stars there situated will set sooner and 

 sooner every night until they disappear for the season. 

 .Vrming the instru)neiit, then, with a power of 160 (a 

 lower eye-piece may be employed to find the object), we 

 will begin by directing it towards the star marked y iu 

 Cetus {vide Map on p. 119). 



Fig. •!.— y Ceti. 



At the first glance, probably, the student will see nothing 

 but a yellowish star of considerable Ijrightness ; but, by 

 careful attention, ho will not be long ere he catches its 

 small companion, seemingly to the left of and just below 

 a horizontal line, passing through the larger star. Its blue 

 or dusky tint will at once strike the observer, as well as its 

 small size as compared with that of its primary. This elegant 

 'pair form what is known to astronomers as a "binary 

 -■.ystem " ; in other words, the stars are physically con- 

 nected, and the smaller star revohes round the larger 

 one — or both round their common centre of gravity — in a 

 very long period, the exact duration of which is as yet un- 

 determined. There an^ other objects of interest in this 

 constellation, but tht- dilliculty of recognising them without 

 the aid of an equatorially-mounted telescope, furnished 

 with graduated circles, compels us to omit reference to 

 them in these very elementary pajiers. Among them, G6 

 Ceti may l)e mentioned as a charming pair. It may be 

 found— with numerous other doubles — on Map 3 of 

 Proctor's " Star Atlas." 



Above, and to the right of that jiart of Cetus in which 

 y is situated, will be seen a curved line of three stars (Map 

 on p. 201) ; the chief ones in Aries, the bottom, and 

 le.ast of which is remarkable as being the one of wliich 

 Hooke wrote in IGGt, " I took notice that it consisted of 

 two small stars very near together ; a like instance to 

 which I have not else met with in all the heaven." It is 



almost needless to tell the student that double stars arfl 

 now numbered by thousands. Viewed with a power of 

 100, y Ai-ietis presents the appearance shown in Fig. .'5. 



Fig. 5. — y jVriotis. 



The components of this asterism will be observed to I>e 

 pretty nearly equal in size. The apparently lower and 

 slightly smaller star of tlie two will be seen to be of a 

 grej-ish hue. If now the observer will follow an imaginary 

 line from y through /3 in the map, it will strike upon 

 star, not lettered there, but fairly well seen by the naked 

 eye to the right of a. This is X, a wide but pretty double. 

 Here, again, the smaller star is more distinctly coloured 

 than thi^ larger one. Forming the apex of a right-angled 

 triangle, with a and \ Arietis (whereof n is at the right 

 angle), is a wide triple star, 1 -1 Arietis. Sweeping where 

 Aries and Triangula are conterminous, several pairs of 

 small stars will pass across the field of view. Some 2° 

 (four times the diameter of the Sun or Moon) above, and to 

 the right of /5, Arietis (as seen by the naked eye) will Ije 

 found a beautiful close double star, which will tax the 

 powers of the incipient observer to see fairly separated. It 

 is 1 79 of Hour I. in Piazzi's Great Catalogue. The yellowish 

 tinge of the larger component contrasting with the blue of 

 the smaller one renders this a very pretty object. 



And while his telescope is directed to this region of the 

 sky, the student will not fail to turn it upon the planet 

 Saturn, still employing the same power. The aspect of the 

 planet as seen in an instrument of the size of that wliicb 

 we are supposed to be ming is shown in Fig. 6. 



Fig. 0. — SatHru, 



It was (li-awn with a 3-in. telescope of the highest class 

 expressly for these papers, and exhibits what the possesso 

 of such an one may fairly expect to see under similar cii 

 cmnstances. A little careful attention will show how th 

 ring is divided into two by a dark line which will be mos 

 ea.sily traceable in what are called the " ansa^ " (or handlci 

 — i.e., in tlie easternmost and westernmost parts of it Th 

 inky-black shadow of the ball of the planet, rfo the right o 

 it, on the rings, and the slight curvature of this shadow 

 will also be made out without much difficulty. Thedarke 

 shading on the southern half of Saturn's globe, and th 

 bright belt on the planet's equator between tliis pola 

 capping and the ring, will be recognisable without difl 



