THE PLANET JUPITER IN OCT. AND NOV. 1880. 
5 
spot, whose motions he watched with the same assiduity as in 
the preceding instances, and deduced a period of 9 h 50 m from 
his new observations. The inference is obvious. He had 
observed objects of different nature, showing a difference of 
motions, for the discordance of nearly six minutes between his 
values cannot possibly he accounted for on other grounds. The 
trivial discrepancy of 10 seconds between his first two values is 
readily explained by errors of observation ; but the large dis- 
agreement with his subsequent calculations is only to he satisfied 
on the assumption that the spot exhibited proper motion. 
Schroter has also left on record an observation of black spots 
crossing the Jovian disc in abnormal periods; and Madler, in his 
Popular e Astronomie has a reference to s imil ar phenomena. 
In September, 1880, the writer commenced a series of obser- 
vations of Jupiter, with the object of noting the peculiar forms 
of the markings, and of generally recording such changes 
as might be presented in his appearance. The telescope em- 
ployed was a reflector of 10 inches aperture, by Browning of 
London. The powers used depended upon the state of the 
atmosphere. Sometimes the performance of the instrument 
was best with 300, but under ordinary circumstances 450 was 
the most effectual ; and at times, when the air was very 
steady and the planet free from that tremulous movement 
so annoying to observers, 500, and even 600, could be used with 
advantage. The usual appearance of the planet was that of a 
globe striped with a variety of dark parallel bands. Whenever 
the large spot was visible, the aspect was different. Its well- 
defined outline and the contrast it offered to the series of con- 
tinuous belts, gave a special character to the view (PI. I. fig. 1). 
In the equatorial region of the planet, there was always a very 
broad and variously marked zone of shading. A mass of detail 
was apparent here, and changes of great extent were evidently 
in progress. The zone was bounded, on both its north and south 
limits, by a dark streak, that on the north side being obviously 
the deeper of the two. Included within these streaks, there 
were fainter patches interspersed with lighter areas and spots. 
The latter were usually slightly on the southern side of the 
equator, while, immediately on the other side and contiguous 
to the north streak, though distinct from it, was an irregular row 
of dusky patches. In the southern hemisphere, the great spot 
was visible adjacent to the great belt (see Fig. 1), and preceding 
this to the southward, there lay a smaller elliptical spot, which 
was discovered by Mr. Barnard, at Nashville, Tennessee, on 
July 24th, 1880. Several faint belts were perceptible on the 
south side of these objects, and the south pole itself was capped 
by a dusky shadowing, or by a numerous array of belts so close 
together as to be inseparable. In the northern hemisphere, 
