SCIENCE. 
i65 
SCIENCE: 
A Weekly Record of Scientific 
Prog r ess. 
JOHN MICHELS, Editor. 
Published at 
229 BROADWAY, NEW YORK. 
P. O. Box 8838 . 
SATURDAY, OCTOBER 2, 1880. 
We are pleased to remark some prospect of renewed 
astronomical activity at the Dearborn Observatory, 
Chicago. This institution was, for a period of more 
than ten years, in possession of the largest refracting 
telescope in existence — the object glass of which has 
an aperture of eighteen and one-half inches. The 
great telescopes which have since been built, 
and are now in process of construction, have 
the apparent effect of dwarfing the Chicago tele- 
scope, which, at the time it was made, was a 
great advance on every thing that had preceded 
it. There seems to be the best of reason for 
doubting, however, whether any other instrument at 
present in existence is surely superior to the Chicago 
refractor for efficient astronomical work. Mr. S. W. 
Burnham, distinguished for his researches in double 
stars, speaks with authority in this matter — “ I know 
of no object, faint or otherwise, which has been seen 
at Washington or elsewhere, that cannot be seen per- 
fectly here [at Chicago] and accurately measured.” 
Professor Newcomb, in his “Uranian and Neptunian 
Systems, Investigated with the 26-inch Equatorial of the 
United States Naval Observatory, Washington,” re- 
marks that Ariel and Umbriel, the inner satellites of 
Uranus, “ are visible only when the atmosphere is 
very fine, and are then difficult objects,” and considers 
it very doubtful whether these objects have ever been 
seen with an aperture so small as twelve inches. 
Director Hough, of the Dearborn Observatory, states 
that near the time of the planet’s opposition, these satel- 
lites can readily be seen and measured, under ordinary 
atmospheric conditions, with the Chicago telescope. 
If, as is quite possible, the Chicago refractor should 
prove to be quite as effective in actual observation as 
some of the larger telescopes of a later day, we shall 
have another of those instances frequently forced 
upon the astronomer, wherein his computation of the 
adequacy of a particular instrument does not tally 
with its observational effectiveness. Every astronomer, 
then, must regret that so competent an instrument | 
must, through lack of endowment, be lying mainly 
idle, or, at the most, only employed by those who are 
able to turn it to scientific observation without 
pecuniary compensation. The valued work of Mr. 
Burnham with this instrument, in the discovery and 
observation of double stars, is well known. • Professor ; 
Hough, in connection with Professor Colbert, con- 
ducted a series of observations of Jupiter at the late 
opposition. Owing to the discordance in the deter- 
minations of the ellipticity of the planet’s disk from 
observation, their attention was given to a new deter- 
mination of this quantity, with these results: 
By Professsr Hough 1 — 16.23 
By Professor Colbert 1 — 16.73 
The English Nautical Almanac uses the value 
1-13.71, while the value 1-16.40 is adopted in the 
American Ephemeris. With the same magnifying 
power, 638 diameters, the absolute polar and equa- 
torial diameters of the planet were observed to be, 
for the mean distance of Jupiter from the Sun: 
Polar. Equa’l. 
By Professor Hough 36". 319 38". 704 
By Professor Colbert 36". 030 38". 316 
Assuming a solar parallax of 8”.8i, the measures of 
Professor Hough give for the equatorial diameter 
90,570 miles, and for the polar diameter 85,000 
miles. 
Measures of the angle of position of the north edge 
of the equatorial belt show that it had the same direc- 
tion around the entire circumference, and that this 
direction (exactly parallel to the planet’s equator) was 
maintained throughout the entire opposition. Very 
complete measures of the apparent latitudes and 
widths of the several components of the belt system of 
Jupiter were also made, the great red spot co-inciding 
very nearly with one of these belts. The reduced 
measures of apparent latitude show very clearly that 
the belts were arranged symmetrically on either side 
of the equator, three being in the northern and three 
in the southern hemisphere of Jupiter. The report on 
these observations is accompanied with wood-cuts 
showing the red spot, the belt system, and, to some 
extent, the structure of the great equatorial belt. 
From the observations of this spot, Professor Colbert 
has computed the time of rotation of the planet on 
its axis: he finds it to be gh. 55m. 34.2s., differing 
about eight seconds from the value hitherto consid- 
ered the most probable. 
Micrometric measures of the diameters of the four 
satellites of Jupiter were made on three nights, the 
resulting values being, at mean distance of the planet: 
1. II. III. IV. 
i".H4 o".98o r.778 i:\457 
The actual diameters of the satellites given by 
these measures are 2610, 2290, 4160, and 3410 miles, 
respectively. 
But the superior quality of the object glass of the 
Chicago refractor is more effective with such objects 
as the satellites of Uranus; micrometric observa- 
tions were secured as follows : 
Of Ariel, on four nights. 
Of Umbriel, on one night. 
Of Titania, on eight nights. 
Of Oberon, on seven nights. 
And this, notwithstanding that the observations were 
begun late in the opposition, and were interrupted by 
an unusual amount of cloudy weather. We should 
like to see the superior light-gathering power of this 
object glass turned toward systematic figuring of the 
fainter nebulae. 
We may mention the meridian circle of the Dear- 
