320 



♦ KNOWLEDGE ♦ 



[Nov. 23, 1883. 



elliptical outline is seen to be continuous — save, of course, 

 where the planet itself is superposed on it. The rings are 

 known to astronomers as A, B, and C ; A being the outer 

 ring, separated from B, the broad bright inner one, by 

 Cassini's division, and C, the innermost crape ring, which 

 we have just been describing. Ring A itself has been seen 

 to be further cut into two Vjy a division known as Encke's ; 

 but assuredly this has never been ttl'ected with a 3-inch 

 telescope. 



Saturn, as may be learned from every primer of astro- 

 nomy, is attended by eight satellites, of which three are 

 wholly invisible save in large and powerful telescopes. We 

 lind, however, that in speaking of those named Tethys, 

 Dione, and Rhea, on p. 221 of the first volume of Know- 

 ledge, as " too severe tests for a 3-inch object-glass," we 

 were really doing an instrument of that size an injustice. 

 By hiding Saturn behind a very thick wire in the eye-piece, 

 or by any cognate contrivance, Tethys and Dione may 

 sometimes be glimpsed on a dark night. Rhea was even 

 visible in the bright moonlight while the sketch of the 



little easier, but will be best seen when at its greatest east 

 or west elongation. Titan shining as a small eighth magni- 

 tude star is practically always visible. It occasionally trans- 

 mits the disc of Saturn, and under these circumstances its 

 shadow has even been seen as a tiny black dot, crossing 

 the face of the planet, with only 2^ in. of aperture. The 

 light of lapetus is (from some cause at present imper- 

 fectly understood) variable. This satellite is very markedly 

 brighter when at its western elongation. 



Such are the most salient features of this wonderful 

 planet, as seen in a small telescope. We can only express 

 a hope that our description of them may set the student 

 seriously to work examining them for himself, with the best 

 instrumental means he can obtain. The interest which the 

 contemplation of so wonderful and beautiful an object must 

 perforce excite, will, almost of necessity, induce a desire for 

 fuller information concerning it. For such information, of 

 a practically exhaustive character, no better or more inte- 

 resting a work could possibly be found than " Saturn and 

 its System," * by the Editor of this journal, which has been 



planet given on the previous page was being made, and we 

 fancied (although it may have been only fancy) that 

 Tethys sometimes flickered up for a few consecutive seconds 

 at distant intervals. Inasmuch then as, under sufficiently 

 favourable circumstances, the possessor of a first-class 3-inch 

 telescope may hope to perceive four, or even five, out of 

 the eight satellites by which Saturn is attended, we here 

 give a drawing to scale of their orbits, by the aid of which 

 the student may recognise them. 



The arrows show the direction of their motion, in con- 

 nection with which it may be noted that, at first sight, 

 this motion may seem to be retrograde. It must, how- 

 ever, be borne in mind that we are looking at Saturn's 

 south pole, and, so to speak, viewing the orbits of his 

 moons from underneath. In 1899, when the north pole 

 of the planet will be presented to us practically as the 

 south pole is at present, the satellites will be seen to be 

 travelling in the same direction as those of Jupiter, or 

 as our own Moon, ifcc. Tethys and Dione must always 

 be difficult objects in a small instrument, and require, as 

 we have said, the planet to be hidden, and a moonless 

 sky, to be even glimpsed in a 3-inch telescope. Rhea is a 



described, with perhaps as little flattery as ever appeared 

 in a critique, as " one of the most masterly monographs on 

 an astronomical subject in the English language." 



The Railivay Revieio (Chicago, Sept 15) devotes con- 

 siderable space to the discussion of the question of standard 

 time, now occupying much attention in America. It 

 reprints a letter published in the Raihcay World, urging 

 the adoption of noon by Greenwich time as the universal 

 railway standard, and counting from it all round the clock, 

 the twenty-four hours being each simultaneous all over the 

 continent. The suggestion which it advocates, however, is 

 the less sweeping one of Mr. W. F. Allen, secretary of the 

 time conventions, who proposes that North America should 

 be divided into five sections, as follows : — First, the inter- 

 colonial, with a central meridian GO deg. west of Green- 

 wich ; second, the eastern ; third, the central ; fourth, the 

 mountain ; fifth, the Pacific division, the central meridian 

 of each being 15 deg. from that of the next, and the 

 difference of time throughout each being precisely one hour. 



* London : Chatto & Windug. 



