1 877.] Movements of Jupiter's Cloud-Masses, igi 
the swift motions of the cloud-masses enwrapping Jupiter 
(for a velocity of 151 miles per hour exceeds that of the 
most tremendous hurricanes on our earth), it has always 
seemed to me that this one series of observations should 
suffice of itself to show that the phenomena of Jupiter’s 
cloud-laden atmosphere are not due to solar adtion. For the 
rift itself continued, and the changes affedting it continued 
whether Jovian day was in progress or Jovian night. For 
one hundred Jovian days or more, and for one hundred 
Jovian nights, the great cloud-masses on either side of the 
rift remained in position opposite each other, slowly wheeling, 
but still continuing face to face, as their equatorial ends 
rushed onwards at a rate fourfold that of a swift train, even 
measuring their velocity only by reference to the ends remote 
from the equator, and regarding these as fixed. Probably 
the cloud-masses were moving still more swiftly with respedt 
to the surface of the planet below. 
Of course, it is just possible that a great dark rift, 
such as I have described, might appear thus to change in 
position without any actual transference of the bordering 
cloud-masses. Mr. Webb, speaking of a number of pheno- 
mena, of which those presented by the great rift of i860 
are but a few, says that “ they prove an envelope vaporous 
and mutable like that of the earth, without, however, neces- 
sarily inferring” [? implying] “the existence of tempestuous 
winds : even in our own atmosphere, when near the dew- 
point, surprising changes sometimes occur very quietly : a 
cloud-bank observed by Sir J. Herschel, 1827, April 19, was 
precipitated so rapidly that it crossed the whole sky from 
east to west at the rate of at least 300 miles per hour ; and 
alterations far more sudden are conceivable where everything 
is on a gigantic scale.” It does not seem to me altogether 
probable that more rapid alterations would affedt cloud- 
banks covering millions of square miles, than occasionally 
affedt terrestrial cloud-banks covering perhaps a few tens of 
thousands of square miles ; on the contrary, as small ter- 
restrial clouds change relatively in a far more rapid way 
than large ones, and these than cloud-masses covering a 
county or a country, so it would seem that the changes 
affedting our largest cloud-layers would be relatively far 
more rapid than those affedting cloud-masses which could 
(many times over) enwrap the whole frame of this earth on 
which we live. But apart from that, and apart also from 
the important consideration that all such processes as eva- 
poration and condensation, so far as the sun brings them 
about should proceed far more sluggishly in the case of a 
