8 
POPULAR SCIENCE REVIEW. 
which is based on a period of 9 h 55 m 27 s *08, derived from the 
observations of dark spots seen in 1834-5 and 1862. But if the 
motion of the white spot is taken relatively to that of the red 
spot now visible, which rotates more slowly than those of 1834-5 
and 1862, referred to, it becomes even greater ; for during the 
eleven weeks over which the observations extend, the aggregate 
movement will be 586°, or 7° 7 daily = nearly 13 minutes of 
time. This motion has not been uniformly maintained. The 
records show a considerable retardation during the latter period 
of the observations. Let us divide the dates into nearly equal 
intervals and compare the calculated periods from each of 
them : — 
h m 
Observed period, 
h m s 
Oct. 20 . 
Oct. 30 . 
. 11 38 { 
7 28 1 
• 24 rotations 
9 49 35 
Oct. 30 . 
Nov. 8 . 
7 28 
7 48! 
| 22 rotations 
9 50 0 
Nov. 8 . 
Nov. 17 . 
7 48 ] 
8 14! 
j- 22 rotations 
9 50 16 
Nov. 17 . 
Nov. 26 . 
8 14 j 
8 44! 
| 22 rotations 
9 50 27 
Between November 26th and December 3rd, the motion 
seems to have been accelerated, the period being 9 h 50 m , 
exactly, and similar to that of the period from October 30th to 
November 8th. 
Certain trivial, though important, corrections have to be 
applied to these times. Differences in the longitudes of Jupiter 
and the Earth, and in the varying distance and phase of the 
planet have severally to he computed and the resulting values 
applied to the simple observed periods. But the corrections 
required are very small, not exceeding a few seconds, and will 
be properly discussed when the observations have reached a 
more complete stage and are in process of final reduction. 
In Fig. 3 (PI. I.), I have endeavoured to show the appearance 
of the white spot in the equatorial belt on November 28th, when 
it was noted as central on Jupiter. Compared with the dark 
rifts and streaks in its vicinity, the spot is strikingly prominent, 
lying a little south of the equator and breaking into the great 
south belt. In Fig. 4 are shown its several positions as it over- 
took the red spot on the nights of November 17th, 19th, 20th, 
and 21st. On November 19th, the white spot appeared to he 
situated in precisely the same longitude as the red spot. On 
the following night its swifter motion had carried it forward 
considerably in advance of the middle of the red spot, and on 
November 21st it was perceptible under the preceding end. The 
following is the comparison of the observed times of transit of 
