SCIENTIFIC SUMMARY. 
69 
This coincidence is interesting, as last year it was thought that the 
motion of the red spot was gradually accelerating. From the total number 
of observations he derives the value- 
9 h 55 m 34 s, 42 ± 0 S *04 
This value differs by 8 s- 7 from the result of the observations of the 
rotation of Jupiter made during 1862, when from the observation of a very 
permanent white spot there was derived the value 
9 h 55 m 25 s *68 ± 0 S T8 
Of late a considerable number of white spots have made their appearance 
on the dark red equatorial belt. Some of them are beautifully round, and 
resemble satellites in transit, but others are more irregular, and have a 
woollier aspect. These white spots move considerably faster than the red 
spot, every day showing a marked gain. According to Schmidt, the time 
of revolution of these white spots is 
9 h 50 m 0 9 
So that they gain thirteen minutes per day on the red spot. This is con- 
firmed by the results obtained by Mr. W. F. Denning, who finds the time of 
rotation of three of these spots to be 9 h 50 m 5 s , 9 h 50 m 6 s , and 9 h 50™ 3 s 
respectively. 
Towards the middle of October a number of round dark spots, at times 
almost black, made their appearance in the northern hemisphere of the 
planet. These spots greatly increased in number, and towards the end of 
November they formed, according to Mr. W. H. M. Christie, a regular dark 
belt. From the observations of Messrs. Williams, Eiger, and Denning, they 
seem to move with the same velocity as the equatorial white spots, having a 
time of rotation of 9 h 50 m 5 s . According to Prof. Schmidt, however, some 
of the black spots move slower than' the white equatorial spots. 
Following the red spot there is a pale greyish spot, and also a whitish 
streak ; both these seem to move with the same velocity as the red spot 
itself, so that it would seem that the variation in velocity affects the 
different belts as a whole. 
At the present time, therefore, Jupiter presents an interesting subject 
for critical examination with large instruments, and a good deal may 
be expected to be learned when all the recent observations are critically 
discussed. 
Hartwig's Comet . — This comet was discovered by Herr Hartwig at the 
Strasburg Observatory, on the evening of September 19, 1880, and by Prof. 
Harrington at the Ann Arbor Observatory on the following night. It was 
a bright comet, of considerable size, and for several days during the be- 
ginning of the month could be easily seen with the naked eye, being a little 
brighter than the well-known nebula in Andromeda. It was not discovered 
until more than three weeks after its perihelion passage, so that when seen it 
was quickly receding from the Earth, thus rapidly becoming fainter, and by 
the end of the month it had become so faint that it could only be seen in 
the most powerful telescopes. It was a bright diffuse comet, with a rounded 
nucleus, and a tail nearly two degrees in length. 
Shortly after its discovery, Prof. Winnecke pointed out the strong 
resemblance between its orbit and that of the bright comet of 1506, and 
