190 Movements of Jupiter's Cloud-Masses. [April, 
happened that instead of two spots, in different latitudes, a 
well-defined dark streak or opening, having its two extremi- 
ties in different latitudes, has remained long enough to be 
observed during several rotations of the planet. In these 
cases it has been observed that the end of the streak nearest 
the Equator has travelled fastest, not only absolutely, but 
in longitude, insomuch that the position of the streak has 
notably altered. 
Thus, in February, i860, Mr. Long, of Manchester, no- 
ticed across a bright belt an oblique dark streak. “ Its 
position ” (I quote from a paper of my own written six years 
ago, when as yet the theory now before us was in its infancy) 
“ might be compared to that of the Red Sea on the globe 
of the earth, for it ran neither north and south nor east and 
west, but rather nearer the former than the latter direction. 
The length of this dark space — of this rift that is, in the 
great cloud-belt — was about ten thousand miles, and its 
width at least five hundred miles ; so that its superficial 
extent was much greater than the whole area of Europe.” 
It remained as a rift certainly until April 10th, or for six 
weeks, and probably much longer. It passed away to the 
dark side of Jupiter, to return again after the Jovian night 
to the illuminated hemisphere, during at least a hundred 
Jovian days; and assuredly nothing in the behaviour of 
terrestrial clouds affords any analogue to this remarkable 
fa (ft. “ This great rift grew, lengthening out until it stretched 
across the whole face of the planet, and it grew in a very 
strange way ; for its two ends remained at unchanged dis- 
tances from the planet’s equator, but the one nearest to the 
equator travelled forwards (speaking with reference to the 
way in which the planet turns on its axis), the rift thus 
approaching more and more nearly to an east and west 
direction.” The rate of this motion was perhaps the most 
remarkable circumstance of all. Mr. Baxendell, one of the 
observers of the rift, and one of our most experienced 
telescopists, thus describes the changes seen in the belt : — 
“ Since Mr. Long first observed the oblique streak on 
February 29th, it has gradually extended itself in the direc- 
tion of the planet’s rotation, at the average rate of 3640 miles 
per day, or 151 miles per hour, the two extremities of the 
belt remaining constantly on the same parallels of latitude. 
The belt also became gradually darker and broader.”* 
Apart from the evidence afforded by this rift respecting 
* Two pictures of this belt — as seen March 12th, i860, and April 9th, i860 
— will be found in my article on “ Astronomy,” in the Encyclopaedia Britan- 
nica, vol. ii., p. 808. 
