December, 1903.] 



KNOWLEDGE 



271 



periods of llh. 40m. 30s., llh. 51m., and rather more 

 than 12h., from various markings he followed, but these 

 results are very doubtful, and astronomers have never 

 attached any weight to them. 



Schwabe, of Dessau, observed markings in 1847, and a 

 round bright sj)ot near the S. limb was noticed by Busch 

 and Luther in 1848. Certain dark patches were seen by 

 Bond in 1848 and 1854, and re-oUscrvcd by De la Kue in 

 185t). Lassell, Jacob, Coolidge, ]»:iwes, Sccchi, and a few 

 others also detected spots at about tlie same period. 



Lassell wrote in 1857, January 8 : "There are certainly 

 chronic changes of great magnitude occasionally occurring 

 on the face of this planet." 



Dawes stated* in 1858, January : "I have observed a 

 well-marked light spot in the S. hemisphere of Saturn 

 which I estimated to be at about 40° or 50° of S. latitude. 

 It was nearly in the axial line on January 11, at lOh. 30m. 

 G.M.T., and again on January 14, llh. 20m., on both 

 occasions a little past it." 



Lassell viewed Saturn with a magnificently defined 

 image in his 20-feet reflector of 20 inches aperture, powers 

 430 and 650, on 1858, April 17, just before 9 p.m., and 

 said,t " Near the preceding limb, and a little south of the 

 equatorial dark belt, was a brighter portion, too large to 

 be called a spot yet sufticiently defined or marked out to 

 be useful in determining the rotation of the planet." 



The white spot seen by Dawes on 1858, January 11 and 

 14, and that observed by Lassell on April 17 of the same 

 year, were ]irobalily identical objects, with a rotation 

 period of nearly lOh. 25m. Dawes' two observations 

 sufficiently prove that the marking exhibited a rate not 

 differing greatly from lOh. 243ni. 



Prof. Asaph Hall attentively studied Saturn during 

 the fourteen years from 1875 to 1889 with the great 

 Washington refractor of 26 inches aperture by Alvan 

 Clark, and found that the ball of the planet presented very 

 few changes, the most remarkable being the outbreak of 

 an equatorial white s])ot, first seen on 1876, December 7. 

 Prof. Hall paid that " on poor nights when the image is 

 blazing and unsteady we can see and can imagine many 

 strange things about this wonderful object." The white 

 spot was watched from 1876, December 7, to 1877, 

 .lauuary 2, by Profs. Hall and Eastman at Washington, by 

 Mr. A . G. Clark at Cambridgeport, and was also seen by 

 several other A merican observers. A number of transits 

 were secured, and from these it appeared that at intervals 

 of three days the spot arrived at the planet's central 

 meridian 16 minutes earlier than before. Prof. Hall found 

 for the time of rotation lOh. 14m. 23-8s., with a probable 

 error cf only 2-3 secs.;|: 



In 1891 and three following years a considerable numlier 

 of bright and dark spots near the equator and in certain 

 other latitudes of Satuni were discerned by Mr. A. S. 

 Williams, of Brighton, with a 6i-inch reflector. Tbe results 

 were discussed and summarised in Mon/hly Notices, LIV., 

 p. 298—314, and LV., p. 354-67. § The rates of the 

 various objects differed slightly, ranging between about 

 lOh. 13m. and lOh. 16s., but they appeared to present a 

 satisfactory agreement with the earlier values of Herschel 

 and Hall. It is only fair to mention, however, that several 

 other exi>erienced observers || employing powerful telescopes 

 quite failed to see any spots on Saturn at about the same 

 period. It is not, however, our intention to discuss the 



* Monthlii Notices, XVIII., p. 72. 



t Ihid., XVII I., p. 231. 



X Axlronomische Nachrichlen, No. 21 US. 



§ See also Ast. Nack., No. 3051. 



jl Prof. Barnnrd, vvnting in 1903, .Tune, says that during all the 

 obanrvations ho had previously madr of Saturn he had novor seen any 

 inarliiiig that <'Ould be used for deionnining the rotation period. 



question whether planetary markings can be easily seen in 

 a 6i-inch telescope, and their individual forms traced wliile 

 instruments of 36 inches and less fail to show any vestige 

 of such objects. The remarkable efficacy of small telescopes 

 in revealing planetary detail has often been admitted, but 

 comparisons at the observatories of Mount Hamilton, 

 Princeton, Chicago, and elsewhere have proved the un- 

 doubted superiority of large instruments. 



lu 1896 and 1897, M. Antoniadi, using the 9f-inch 

 refractor of the Juvisy Observatory, observed dusky con- 

 densations on the north equatorial belt, and from these 

 he ascertained the rotation period as a little more than 

 lOh. 14m. 



During the last quarter of a century Prof. Hall's deter- 

 mination has been regarded as a standard value for tbe 

 rotation of Saturn. True it was based on few observations 

 extending over twenty-seven nights only, and upon an 

 object obviously variable, for while at first it was round 

 and 2 or 3 seconds of arc in diameter, it resolved itself at 

 last into a bright streak. 



The planet has been traversing the southern signs of 

 Scorpio and Capricornus during the last few years, and its 

 low position in the sky has had the usual effect in im- 

 pairing tbe definition so much that observers in northern 



Saturn, 1903, August 21, llli. 



latitudes have not been successful in detecting any irregular 

 markings on the disc. The present opposition has, how- 

 ever, provided developments of very important and inte- 

 resting character. Prof. Barnard was examining Saturn 

 on June 15. 21h., G.M.T., with the 40-iuch Yerkes re- 

 fractor, when he discovered a decidedly marked white spot 

 haU'way between the central meridian of the planet and 

 the following limb. Clouds came over, but the marking 

 was recovered on June 23rd, when its passage across the 

 central meridian occurred at 21h. 42in., Or.M.T. It was 

 seen again on June 24th, and the central transit observed 

 at 18h. 58m., G.M.T. On July 1st the writer, at Bristol 

 (uuawai-e of previous observations), noticed a bright spot 

 on Saturn which must have been central at about 14h. Im., 

 though it had passed to some distance west of the central 

 meridian when first seen. This object was subsequently 

 assumed to be identical with Barnard's spot of June 23rd, 

 for eighteen rotations of lOh. 14im. would accord well 

 with the interval elapsed between fhe pair of tnmsits, but 

 further observations disclo.sed the surprising fact that 

 the new markings were moving far too slowly to l)e con- 

 sistent with the usually accepted rate of Saturn's rotation. 

 Graff, of Hamburg, pointed out in Ast. Nach. that tbe 

 period of Barnard's spot, deduced from a few of the 

 earlier observations, was about lOh o901m., while Sola, 

 of Barcelona, from more materials, found the value 

 lOh. 38-4m. There have been several spots visible, both 



