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38



SCIENCE.



JUPITER.
By Prof. G. W. Hough, Director Dearborn Observatory.

During the present opposition of Jupiter, the disc ex-
hibits a variety of phenomena of interest to the practical
astronomer.

Although this planet has received a good deal of atten-
tion during the past century, yet, but few new facts have
been added, with regard to its physical aspect, since the
time of Sir Wm. Herschel.

It appears to be the generally accepted idea that its
surface is subject to sudden and extraordinary changes,
sometimes accomplished in a few days or even a few
hours. New belts are alleged to have been formed or to
have disappeared in the course of an hour or two.

We believe conclusions of this kind have been too
hastily drawn from the obstructions.

Owing to the rapid rotation of Jupiter, the various spots
and markings follow each other so closely that one
might readily imagine that what he saw was subject to
change under his eye.

The great red spot, which has been an object of so
much interest since 1879, becomes visible, in the Chicago
telescope, at 2h. 25m. from the meridian of the planet,
when its length is about one second of arc. As the rota-
tion carries it further on the disc, it gradually increases
in size, until, when on the meridian, it subtends an angle
at opposition, of 15 seconds. The smaller spots and
markings, of course, become most conspicuous when
near the meridian of the disc.

The visibility of objects depend, very much, also,
on the condition of the seeing. Sometimes the smaller
spots are invisible for weeks, simply because the
seeing is not good enough with limited optical power,
and not because there has been any radical change on
the surface of the planet. Its distance from the earth is
another important element in modifying the appearance
of phenomena. After conjunction, the great Equatorial
Belt and Red Spot are first seen and, as the earth ap-
proaches nearer, other markings gradually appear, until
the time of opposition, the greatest variety of phenomena
is noticeable.

From September, 1879, when micometer measurements
were first begun, with the Chicago Refractor, on the
markings of the disc, considerable change has taken
place in its appearance at different times. But all changes,
whether due to the distance of the planet from the earth,
variable seeing, or other causes, have been slow and
gradual.

The most noticeable change has taken place in belt
No. 3 situated 6" north of the equator. This belt, which
was not conspicuous in 1879, gradually increased in
width and distinctness in 1880, until at the present time
its width is about 2". 5 ot arc, and of the same color as the
equatorial belt, viz.; reddish brown.

The equatorial region situated between the two out-
lines of the equatorial belt has been subject to consider-
able change, but the margins of the belt have not sen-
sibly varied in width or latitude during the past three
oppositions.

The great red spot, a conspicuous object even in a small
telescope, is alleged to have materially changed in length
during 1879, anc ' again in 1880, but numerous micrometer
measurements do not confirm this statement.

The following are the mean results, reduced to the
mean distance.

Length. No. of Breadth. No. of Latitude. No. of
Obs. „ Obs. , Obs.

1879 12.25 9 3.46 8 —6.95 8

1880 11.55 20 3.54 10 —7-14 12

1881 11.50 8 3.49 3 —7.41 7

These numbers indicate a small possible displacement
of the center in latitude, but it would be premature to
assume such to be the case.

The color of the spot is reddish-brown ; however, when



the seeing is unusually good, it appears almost a light
pink.

The oval-shaped white spots, a number of which were
observed in 1880, are quite numerous at the present time.
They are about one second of arc in length and are gen-
erally difficult objects to observe.

The following spots have been seen on belt No. 6.
Latitude 9". 5 to 12". 6. They pass the meridian of
Jupiter after the great red-spot as follows :

h. h. h. h. h. h. h. h.

+ 2,8 4- 3.0 4- 3.3 + 4.0 + 4.7 + 5-2 + 5-5 +5-8

There are also two white spots — more easily seen —
near the great red spot in latitude 9". 63 and longitude
oh. 36m. and +oh. 24m.

The two white spots situated in latitude 3". o south
of the equator, which were observed in 1879 and 1880,
were first seen this year on July 22. They appear to
make a complete revolution around the planet in about
forty-five days, corresponding to a rotation period of 9I1.
50m. 9 sec.

These spots, which are both occasionally seen at the
same time, appear to be fixed relatively to each other.

The difference of longitude was measured with the
micrometer as follows :
1880.
July 24, +23.5m.
Nov. 8, + 22.6m.

1881.
July 22, + 27.5m.
Nov. 26, 4- 27. 5m.
Dec. 10, +23.om.

The fact that they have maintained for a year and a
half the same relative position, and at the same time
apparently drifted with a velocity of over 260 miles per
hour, would seem to disprove the old theory that they
are clouds floating in the atmosphere of the planet.

From observations made during the present opposi-
tion, it is probable that all the matter between the two
margins of the equatorial belt, whether in the form of
white spots or dark ones, moves with the same velocity,
viz. : a period of 9h. 50m. 9 sec. And it is possible that
the belt itself partakes of this motion.

The rotation period of the planet, deduced from our
observations on the red spot, made in 1879 and 1880,
was 9h. 55m., 33.2 sec. + 0.09 sec. -//7 m which t is the
number of days after Sept. 25, 1879. The observations
during 1880 showing that the spot was retrograding
with an accelerated velocity.

This formula? is found to be essentially correct for
the present opposition.

The "mean" period for Dec. 14, 1881, comprising
an interval of 811 days, being gh. 55m., 35.80 sec. from
observation and 9h. 55m. 35.76 sec. from the formula?

Assuming the rotation period as above, the centre of
the spot has retrograded more than fifty degrees since
Sept. 1879, not uniformly, but with an accelerated velocity.
It seems difficult to account for this fact on any known
hypothesis.

IMPROVEMENTS OF PLANTE AND FAURE'S
STORAGE BATTERY.

In a previous number of " Science" No. 57, July 30th,
1881, we gave excellent directions for making Plante and
Faure's storage batteries. — In a recent paper before the
" Society of Arts, of London, Professor S. P. Thompson
states that almost any oxide or hydrate of lead will answer
for use in the Faure battery— Litharge will answer if suffi-
ciently finely divided for being painted on. Litharge mixed
with a small proportion of binoxide of manganese works
well. The most satisfactory cells I have yet tried were
made by painting the lead plates with a coat of the brown
peroxide itself, which is obtainable in commerce, although
its cost is greater than that of red lead or litharge.




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