THE PLANET JUPITER IN 186C-70. 
129 
of their hue on occasion of the fine display on Nov. 16 ; and I 
thought them purplish on the following night. For variations 
in depth of shade, or breadth, no standard of comparison 
existed except the north temperate belt, which certainly wore 
a more uniform aspect ; assuming the absence of change here, 
it was frequently perceptible in the torrid belts. For instance, 
on Dec. 11, I have noted that they were both much less con- 
spicuous than formerly, and only about half the breadth and 
darkness of the north temperate belt ; but in the next observa- 
tion, two nights afterwards, the contrast was not so striking: 
subsequently, that belt is frequently recorded as stronger and 
darker than either of them, though without so striking a differ- 
ence except on Jan. 5 and Jan. 12, when the recurrence of that 
proportion is expressly mentioned. These changes of aspect 
were at times very rapid ; for instance, on Dec. 25, at 8h. Gf.M.T. 
the north temperate and the two torrid belts were for once 
equal, but at 9h. 45 m. the latter had recovered its accustomed 
deeper tone. In such apparent variations it is not always easy 
Fig. 1. 
[Nov. 16d. lOh. 35m.' 1 
Fig. 2. 
Noy. 17d. lOh. 35m. 
to distinguish between the optical effect due to rotation and the 
results of actual local disturbance ; in many cases both may 
have been combined : a remark which may be extended to 
every portion of the visible hemisphere. On Feb. 25, for the 
first time, these two belts were noticed to be relatively unequal, 
the south being considerably darker than the north at 6h. 55m. 
and 7h. 45m., but at 8h. 15m. the difference had become but 
slight ; and on the following evening at 7h. 20m. both were 
equally feeble. March 5 and March 11 the south was again 
rather the darker. The only estimate I find of their apparent 
dimensions was on Feb. 12, when I thought that the two 
together amounted to more than J- but less than ^ of the whole 
central region. 
The intervening space, which we regard as the Equatorial 
Zone , has been the scene of the phenomena which have attracted 
such general attention. In the first place its colour has been 
so marked that it would force itself upon the notice of even a 
careless observer. I saw it Feb. 5, with as low a power as 11Q. 
VOL. IX. — NO. XXXV. K 
