NATURE 
[March 30, 1871 


THE PLANET JUPITER 
INCE the earliest days of telescopic investigation, there 
has never been a period in which this magnificent planet 
has been subjected to such an extended scrutiny as the 
present. Telescopes of all sizes and powers, and eyes of 
all degrees of sensitiveness and accuracy, are being 
directed night after night—or rather would be so, but for 
the proverbial uncertainty of our English climate—towards 
the splendid gem of the south-eastern heaven. Such is 
the natural result of that unexampled diffusion of a taste 
for astronony, and of the equally unprecedented multipli- 
cation of telescopes of considerable pretensions, which is 
characteristic of the present time, and which isso gratify- 
ing to the lovers of physical science. 
* This state of things, however, it need not be said, does 
not date from the present apparition of the planet. It is 
merely a renewal of the attention which was directed to 
the same object during the preceding winter, and it is 
the character of the results obtained during that former 
period, which has led to the ensuing remarks. 
It may be reasonably thought that a comparison of such 
drawings as are generally attainable, professing to repre- 
sent the planet during its late appearance, is not very 
satisfactory ; and that greater agreement might fairly have 
been expected. Every observer must be presumed to 
have done his best: yet deviations exist of no incon- 
siderable magnitude. There must be some reason for 
these discrepancies ; and it will be worth our while to 
inquire into their nature, while, at the same time, we would 
carefully avoid anything like an implied depreciation of 
any individual result. 
~ In the first place, as regards colour, there is little diffi- 
culty in seeing that a considerable margin must be left for 
uncertainty. We meet with unpleasant statements from 
time to time as to the prevalence of colour-blindness, or at 
least what might be called colour-perversion, or colour- 
partiality, in some modification or other, to a greater 
extent than might have been supposed. And inde- 
pendently of this, there may be some dissimilarity of tint 
in images formed respectively by the achromatic and the 
reflector, though perhaps less than some persons might 
expect ; since the blue rays which usually go astray in the 
former instrument are also absorbed by the silver film of 
the latter, so that there will bea prevailing complementary 
orange, however feeble, in the light that forms the image 
in either case. There will, however, be this advantage— 
and a considerable one—on the side of the reflector, that 
the blue light, in place of forming an unpleasant fringe, 
entirely disappears, leaving a delightfully colourless field 
in the use of the higher powers. Refractors may also 
differ somewhat in their mode or degree of correction, 
and consequently in the uncompensated tint ; and in either 
construction eye-pieces may be chargeable with deficient 
achromaticity. So that on the whole we can scarcely be 
surprised at some differences in the results as faras colour 
is concerned. 
But there would seem to be other and more influential 
reasons for the want of correspondence, as affecting form 
and position. One may be that all observers do not see 
equally well : not referring by this expression to clearness 
of eye, though in this there may be many degrees, but to 
the habit of attention. Where one man, for example, 
merely notes concerning three or four objects that they 
are not all of the same size ; another will almost instinc- 
tively estimate their proportionate difference in magnitude. 
One observer again may be impressed with the proportions 
of the objects, but may miss those of their mutual dis- 
tances ; nor, again, are the estimates of different observers 
equally entitled to confidence. There are eyes, too, very 
good ones for other purposes, which are less successful 
than would have been expected in the discrimination of 
minute planetary markings, a fact not easy of explanation. 
But besides this source of discrepancy, another exists 
in the fact that all observers do not draw equally well ; 
or rather it may be feared that but few draw well at all. 
It is much to be regretted that a certain amount of artis- 
tic skill is not considered absolutely necessary in a liberal 
education ; the advantage and pleasure derivable from it 
in after life are so obvious that it may well be questioned 
whether some of the time that is spent in mastering clas- 
sical and mathematical niceties of an extremely unservice- 
able and unpractical nature, might not be better expended 
in the acquirement of the most useful art of design. It 
ought to be remembered, also, that not only a general 
facility in observation and delineation is requisite, but 
that something depends upon that special training which 
results from familiarity with the individual object. Even 
a careful observer, whose attention had been chiefly turned 
to objects of another kind, might not recognise as much 
of planetary markings at first, as after he had studied and 
learned their character ; and on the other hand, a com- 
petent artist might produce inaccurate work during his 
early acquaintance with the telescope, simply from the 
unfamiliar aspect of what he has to represent, as com- 
pared with anything which he has been accustomed to 
delineate. 
When, therefore, all these sources of discrepancy are 
taken into account, the differences in instruments, in eyes, 
in hands, and in experience, it is no longer matter of sur- 
prise that the results already obtained with regard to this 
planet are less satisfactory in points of mutual agreement 
than would have been desirable. It may be hoped, and 
to a certain degree expected, that we shall do better in 
future. Inexperience is a fault that will disappear of itself ; 
and it would be well if the unpractised observer would be 
content to expend a little time and trouble in making tenta- 
















This sketch is copied from a drawing bearing the date of 1870, De- 
cember rg4 11h ro". It may serve as an illustration of some of these 
remarks, though it makes but little pretension to accuracy. 
tive drawings before he considers them worthy of taking 
rank as representations of the planet. Imperfect attempts 
are, nevertheless, often deserving of preservation, as 
recording, as far as they go, something that may not be 
seen again, and thus acquiring a relative value. The 
remarks which follow may be thought to require some 
apology, especially after what has been said as to some of 
the causes of discrepancy ; but it is hoped that their pur- 
port will not be misapprehended. It is well known that 
success in observation is much more readily obtained by 
those who have some previous idea as to what they may 
fairly expect to see; and on this ground the ensuing sug- 
gestions may be permitted, as the result of considerable 
familiarity with the object. They claim no higher cha- 
racter than suggestions—open as freely to contradiction as 
confirmation ; and their object will be accomplished if 
they are found to give some aid to the unpractised 
amateur ; the skilled observer will forgive them if he finds 
them needless, or correct them where they may be in 
error. They are deduced from the observations of forty- 
three nights, from 15th October, 1869, to 4th April, 1870, 
in the use of a With silvered glass speculum of 9} inches 
