4 
TOPULAR SCIENCE REVIEW. 
periods of 9 h 55 m 34 s , the white equatorial spots are only 
9 h 50^ m , and the black spots in the north hemisphere only 
9 h 48 m . The smaller spots have, therefore, a swift proper 
motion from west to east around the planet, and they have been 
seen, on several consecutive nights of observation, to overtake 
the red spot, to pass rapidly by it, and then to precede it by a 
distance increasing with every successive epoch. These facts are 
thoroughly well authenticated by the accordant results of 
several diligent observers. 
That phenomena of such striking aspect and indicative of 
stupendous changes in the atmospheric envelope of the planet 
should have so long escaped the frequent and vigilant scrutiny 
its importance greatly demanded, is very surprising when we 
consider the host of adequately powerful telescopes which are 
again and again directed to Jupiter at each recurring opposition. 
For there is no sufficient reason to think that the curious details 
recently observed are of very rare character, and special to our 
own time. Notwithstanding their present very distinct and 
palpable occurrence, we have every right to assume that they 
are the simple evidence of what is constantly manifested in the 
physical aspect of the planet. Look at him whenever we will, 
we shall find some indications of vast disturbances, and (though 
there may be times of comparative quiescence in such phenomena) 
they will occasionally he so conspicuous as to call for particular 
comment. But the more minute of these appear to have eluded 
observers in past years, and it is only now that the apparition 
of the great red spot has so fully aroused interest that they 
seem likely to receive a full investigation. We shall certainly 
learn something of the singular phenomena occurring on the 
planet by their means. The complexity of spot-motion which 
the observations are unfolding, have their explanation ; and this 
may be forthcoming when the results come to be collated and 
compared in the final analysis. 
We have said that former observers had overlooked these 
important facts. We mean by this that the matter had never 
been discussed with any thoroughness, and that, though we may 
find amongst old records some brief, vague references to pheno- 
mena similar to those which are now engaging so much notice, 
they never received a due meed of attention. We can go back, 
indeed, more than two centuries, and trace what may have been a 
precisely similar observation to what is now recorded. Cassini, 
in 1665, determined the rotation period of Jupiter as 9 h 56 m ; 
and seven years later, from other spots which he distinguished, at 
9 h 55 m 50 s . These results, so nearly coincident, were evidently 
derived from markings of analogous character to each other, 
and to the red spot which is at present visible on the planet. 
Twenty years later, namely in 1692, Cassini observed another 
