Oct. 8, 1885] 
NATURE 
549 
a series of valuable sketches, which are reproduced in the 
last volume of the Memoirs of the Royal Astronomical 
Society. With regard to Jupiter the declination of the 
planet will be somewhat Jess than during the opposition 
of 1884-5, but the configuration of the belts and the peculi- 
arities of the variable spots will doubtless continue to be 
exhibited with nearly similar prominence as in previous 
years. Saturn, situated in Gemini, and having consider- 
able N. declination, will present a grand display, the rings 
being still widely open and inviting that close and sys- 
tematic scrutiny which is so much needed either to affirm 
or negative some of the questionable details suggested by 
recent observations. 
Observers of Mars are extremely fortunate in possessing 
such valuable memoirs and charts as those of Schiaparelli, 
Terby, Green, and others, which form a comprehensive 
and accurate basis of future reference and comparison. 
The seeming permanency of the chief lineaments on 
Mars and their distinctness of outline have permitted 
observers to assign their forms and positions with great 
nicety. But this has been found practically impossible 
in respect to any of the other planets of our system. 
Their markings are of so variable a tendency or so un- 
certain and _ ill-defined, owing probably to their atmo- 
spheric character, that it is out of the question to frame 
representative views that will serve to express the appear- 
ances observable at any future time. We have accumu- 
lated a vast number. of delineations, including many 
peculiar forms, but these exhibit so much discordance as 
to prove that any attempt to arrange them with the same 
consistency as those of Mars must for the present be 
utterly futile. 
What is essentially required in furtherance of our 
knowledge of areographic features are delineations in 
which the more delicate alternations of light and shade 
are faithfully portrayed. The ensuing opposition, though 
not offering the most favourable inducements for attain- 
ing this end, may yet be utilised as likely to afford its 
share of corroborations to old features and perhaps indi- 
cate some modification of the outlines attributed them 
by former observers. Mr. Marth’s valuable ephemerides 
in the Monthly Notices supply the data wherewith the 
passages of certain prominent markings across the central 
line may be readily calculated from night to night. 
Drawings effected at the telescope and subsequently 
attested by the charts, or independent projections made 
on the basis of the new drawings and then compared 
with previous work will be important as furnishing fresh 
confirmations and additions to oldrecords. Whatever plan 
is adopted, observers must not regard existing delinea- 
tions as Perfectly reliable and prejudice the judgment by 
endeavours to discern the outlines of the spots precisely 
as they have already been figured. Our work should be 
pursued apart from such influences, the aim being rather 
to correct and extend past results, than to follow them 
with implicit faith and mould our new seeings on the 
same pattern. Though much has been accomplished by 
the consecutive labours of the many able and earnest 
students of Martian features, the present state of our 
knowledge is not only incomplete, but considerable un- 
certainty exists as to the more difficult formations com- 
prised in the physical aspect of this planet. 
Jupiter, with so great a diversity of atmospheric pheno- 
mena, some of them rapidly variable, and all influenced 
by the quick rotation of the planet, gives prospect of 
being the subject of increased investigation. Late in the 
preceding opposition the great red spot which had so 
nearly disappeared and had, during the winter of 1884-5, 
assumed the appearance of a red ellipse with interior 
light cloud, showed unmistakeable evidences of increasing 
condensation. The ellipse grew perceptibly darker, and 
the central light cloud disappeared, so that at the end of 
the opposition the spot had almost regained the striking 
aspect it presented a few years ago. The question now 
is has this well-known feature continued to gain ascend- 
ancy during the time the planet has been lost in the sun’s 
rays? Observations in October will furnish a definite 
answer to this question, and the planet should be con- 
fronted with our best telescopes as early as possible, so 
that the necessary evidence may be obtained. The spot 
will pass the central meridian of Jupiter at about the 
following times, and ought to be well seen in small instru- 
ments unless some great changesin an unexpected direc- 
tion have affected its position or appearance in the interim 
since the last observation made here on the evening of 
July 8 :-— 
Red Spot Red Spot 
Da a € Gare Date Cantal 
- Ao) Ih a se) h m. 
Oct. 7 18 34 Oct. 29 16 48 
12 17 43 31 18 26 
17 16) 52 Nov. 3 15 56 
19 18 30 5 17 34 
24 L739) 7 TORTS) 
26 TON 07, fe) 16 43 
With reference to the white spots bordering the dark 
belts, and the other definite markings, they will doubtless 
be remarked as heretofore. Their singular vagaries of 
motion and appearance call for renewed study. The 
varying intensity and colour of the belts and their dis- 
position in latitude should be carefully assigned on 
several dates during each opposition. If this method 
could be persistently followed during many years it 
would supply the material either for tracing out periodical 
recurrences, or proving such changes to be intermittent 
in character. 
During the past opposition of Jupiter much attention 
was directed to the transits of the satellites and their 
shadows. When near mid-transit, III. and IV. are often 
seen as black spots, I. is visible as a grey spot, while II. 
is rarely, if ever, visible otherwise than as a bright spot. 
These anomalies have never received a satisfactory ex- 
planation, and further observations are much required as 
to the relative tints of the satellites when on Jupiter and 
the variations noticeable in different transits. 
Saturn, though not presenting such an extent of con- 
spicuous detail as Jupiter, is yet equally deserving of 
systematic study. The rings and numerous array of 
satellites compensate for lack of detail in the belts. The 
outer division in the ring, called after Encke, supplies us 
with a crucial test object, and one which perhaps has 
originated more difference of opinion amongst observers 
than any other planetary detail of which the existence 
is well assured. Either this division must be liable to 
fluctuate at short intervals or the evidence afforded by 
various telescopes is most conflicting, and suggests how 
careful we should be before accepting individual results 
when not corroborated or supported by undeniable 
testimony. : 
During the last few oppositions a very definite narrow 
dark belt has bounded the southern side of the equator, 
and this has attracted more comment than usual owing 
to its compact and very obvious appearance. This belt 
exhibits no distinct spots, though one or two observers 
have delineated it with marked condensations. The 
fainter belts nearer the pole are so very feeble that their 
existence is sometimes questionable. Indeed the features 
of this planet are of extreme delicacy, and require not 
only very steady air but a thoroughly good eye and in- 
strument to trace them in their more minute forms. 
Some of them are doubtless variable and have given rise 
to the contradictions we have referred to. As to the 
satellites they comprise test objects for telescopes of all 
calibre. The identification of these bodies may be suit- 
ably effected at any hour by means of Mr. Marth’s 
ephemerides (Wonthly Notices, June, 1885). 
W. F. DENNING 
