July 4, 1895] 



NA TURE 



valuable work with the 25'8-inch refractor at Washington is so 

 well known, once said : "The large telescope does not show 

 enough detail." The testimony was not, therefore, unanimously 

 in favour of big telescopes. 



More recently the 36-inch at Mount Hamilton has been 

 eulogised for its fine performance. Mr. Keeler, in January 1888. 

 saiil that the minutest details of .Saturn's surface were visible 

 with wonderful distinctness with this instrument. The 12-inch 

 and 6-inch refractors at the same observatory were found far 

 inferior in capacity to the 36-inch. Prof. Barnard has also 

 staled : " Let the conditions be the best for observing, with the 

 air steady, and the 36-inch is far ahead of the 12-inch.'" The 

 same observer has also remarked : " 350 is the most useful power 

 on Jupiter and Mars, 520 on Saturn." For planetary work he 

 jirefers using the full aperture and low powers. 



We have it on the authority of most of those who have 

 employed both large and small telescopes, and are therefore in 

 ihe best position to speak as to their relative merits, that large 

 instruments in good air will reveal more than small ones. The 

 observer would in preference use the largest instrument for any 

 ' ritical purpose : and this being so, how shall we e.xplain their 

 up])arent failure in regard to planetary details ? Is it that the 

 big telescopes show too little, or that the small instruments 

 exhibit too much ? 



And here it may be noted that only in exceptional cases do 

 we find phenomenal results accruing from the use of small 

 apertures. It is not every one who has a telescope of 6 or 8 

 inches diameter who can discover the various spots and 

 numerous belts on Saturn, or trace the double and often inter- 

 lacing canals of Mars. 



During the last few years numerous dark and light spots have 

 been detected on the ball of Saturn by Mr. A. S. Williams, who 

 used a 6-inch reflector. These have been distinguished when 

 Saturn was nearing conjunction with the sun, and in spite of two 

 unfavourable circumstances — namely, the small diameter of the 

 planet, and its proximity to the horizon. The spots have been 

 seen so distinctly, that the observer has been enabled to describe 

 them individually as bright or faint, small or large, round or 

 oval, iS;c. These observations have not, perhaps, been fully 

 corroborated, though several observers appear to have glimpsed 

 !he markings alluded to. When we consider that many hundreds 

 'if amateurs have been employing their telescopes upon .Saturn 

 without seeing the spots, the affirmative evidence of a few 

 is()late<l |X'rsons can hardly be regarded as conclusive. It is a 

 fact that, if any new feature on a planet, or an unknow^n com- 

 panion to a star were confidently announced, a few of the many 

 observers who looked for it woukl certainly assert they could see 

 it though not really existing. 



I'rof. Hough, with the l8A-inch refractor, at Chicago, made 

 a series of observ.-.l ions in 1884 and 1885 for the special pur- 

 pose of detecting definite markings on Saturn and redetermining 

 the rotation period, but he quite failed to get the necessary 

 data. His statement was : " The belts on the disc of the 

 planet were at times quite conspicuous and very sharply de- 

 fined, but we were unable to find any spot or marking by 

 which to observe rotation." Vet the Monthly Notices for June 1884 

 contain a drawing which gives a numerous array of condensations 

 attached to the dark narrow belt bounding the equator on its 

 southern side. This drawing was made wilh an SJ-inch re- 

 flector, and at about the same period many other observers 

 examined the planet with an entirely negative result as far as 

 the existence of these condensations was concerned. \ drawing 

 was published in \\\<i Journal of the British Astronomical Asso- 

 ciation for July 1894, showing the planet as he appeared on 

 March 26 of thai year in a 12-inch reflector. .\ numerous 

 assemblage of dark bells are shown, and many other observers 

 appear to have seen several comparatively narrow belts. I'rof. 

 Barnard, however, using the 36-inch refractor in re-measuring 

 the dimensions of Saturn and his rings in 1894, was led to pay 

 some attention to the physical appearance of the planet, and 

 significantly remarks : " But one dark narrow belt was seen 

 upon the planet. The black and white spots recently rejiorted 

 with small telescoiies were not seen at any time." It is certainly 

 a remarkable circumstance that the belts and spots, if really 

 existing, cannot be seen in the large instrument. .•\rc llie 

 observers with small apertures suffering from some extraordinary 

 hallucin,ation, or must we consider that the brightness of the 

 image in large telescopes anil inferior definition are sufiicieni (o 

 obliterale very delicate markings? Is the glare sufficiently 

 strong to overcome the slight contrasts of tone readily per- 



ceptible on a fainter image ? Prof. Holden thus expressed him- 

 self in 1891 : "There is no doubt that the belts on Saturn are 

 often marked and mottled with brighter spots. I presume that 

 such spots woukl be as easily seen in a small but jwrfect tele- 

 scope as in a larger one. Seeing such faint markings is entirely 

 a matter of detecting faint contrasts, and these should be de- 

 tected as readily in a small instrument as in ours, if not more 

 readily, except that the large size of our image helps us." On 

 the other hand, I'rof. Young has suggested that faint images 

 are very encouraging to the imagination, and therefore often a 

 source of observational errors. 



Prof. Holden's remarks are tantamount to an admission that 

 large instruments are ineffective on planetary details, for what 

 are delicate markings but "faint contrasts" ? \'et it would be 

 conceived that the 36- inch had proved itself quite ca|>able of 

 dealing with such contrasts, for it is stated by Prof. Barnarti, 

 from observations of Jupiter in .September-October 1894 : " The 

 red spot is fairly distinct in outline, though quite pale — a feeble 

 red. The following end of the spot is quite dark. There are 

 white regions on its surface. The belt south of it seems to be 

 in contact with the spot, if it does not actually overlap it 

 slightly." 



The 36-inch is mounted in one of the finest localities for celes- 

 tial observations, but shows nothing on Saturn but the dark 

 narrow belt situated in the midst of the equatorial zone, while 

 certain telescopes of small aperture reveal the disc furrowed with 

 belts and mottled with spots. Nearly every small telescope 

 shows more than one belt upon Saturn, but the delineations 

 seldom agree as to the number or latitudes of these belts. We 

 ought to expect approximately accordant positions ; Vmt the 

 majority of drawings are hurriedly executed and based on rough 

 estimations, so that they are often found inconsistent. The dif- 

 ' ferences referred to are not, therefore, proof of the non-existence 

 I of the objects depicted, for the same disagreements are found 

 with reference to well-assured formations. In some cases un- 

 doubtedly observers will, perhaps unconsciously, use their 

 imaginatious, as the desire is always to put in as nuich detail as 

 possible. When mere fancy assists the optical powers, the re- 

 sulting drawings are often very pretty and attractive from the 

 number and novelty of the features shown. We can fill in any 

 number of dark belts and bright zones, beaded with spots of 

 various forms and tints, and tone the whole to suit our ideas ; but 

 unfortunately such drawings, though pleasijig to the eye, have a 

 bad influence, since they pervert the truth, and lack that fidelity 

 to nature which could, alone, make them really valuable. 



Mr. Williams, the discoverer of the Satumian spots, has made 

 some hundreds of observations of them, and fully detailed his 

 methods and his results in the Monthly Notices of the R.A.S., 

 liv. p. 297, et sei/. First detecting them in the spring of 1891, 

 he has now followed them during five oppositions of Saturn. 

 The bright equatorial spots apparently show a period of rotation 

 decreasing with the time, for the mean period during 1891 was 

 loh. 14m. 22s., while in 1892 it decreased 44 seconds, in 1S93 

 43 seconds, and in 1894 15 seconds. The care with which Mr. 

 Williams proceeded in his work, and the plan he adopted to 

 avoid bias or preconceived ideas, are explained in the paper 

 alluded t(i, and every one reading his description must be favour- 

 ably impressed with it. If his results are fully confirmed, \\ie.y 

 will deserve to be ranked among the best observational feats of 

 modern times. To have been the first to discover these <lelicate 

 objects in all their variety, to have traced out their individual 

 motions with unwearying persistency year by year, and to have 

 empltjyed all the time a very small telescope, must be regarded as 

 a remarkable attainment. It is to lie hoped that the necessary 

 corroboration will soon be forthcoming. 



I have myself practically endeavoured to afford this, but 

 failed. The spots on Saturn are certainly not visible under 

 powers of 252 and 312 on my lo-inch reflector. The power 

 of 252 is the eye-lens of a Iluyghenian eyepiece, that of 312 is 

 one of the " monocentric micrometer oculars " of J-inch equiva- 

 lent focus by Steinheil of Munich. The latter has a distinct 

 advantage over my Iluyghenian eyepieces. I have sometimes 

 used a Barlow lens in combination with it, increasing the power 

 to about 450, but do not think any .advantage has been gained. 

 I have occasionally had impressions of white spots mottling the 

 bright equatorial zone of Saturn, and occasionally also of faint 

 condensations in the dark belts ; but as to seeing the.se details 

 outright, and obtaining their times of tran.sit with all the cer- 

 tainty of a definite s|K)t on Jupiter, I have quite failed. I am 

 induced to believe, from a number of observations dedicated to 



NO. 1340, VOL. 52] 



