MOVEMENTS OF JUPITER'S CLOUD-MASSES. 83 



Thus, in February, 1860, Mr. Long, of Manchester, noticed 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 10,000 miles, and its width at least 500 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 behavior of terrestrial clouds affords any analogue to 

 this remarkable fact. " 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 distances from 

 the planet's equator, but the one nearest to the equator traveled for- 

 ward (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 de- 

 scribes the changes seen in the belt: " Since Mr. Long first observed 

 the oblique streak on February 29th, it has gradually extended itself 

 in the direction of the planet's rotation, at the average rate of 3,640 

 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 the swift 

 motions of the cloud-masses enwrapping Jupiter (for a velocity of 

 151 miles per hour exceeds that of the most tremendous nurricanes on 

 our earth), it has always seemed to me that this one series of obser- 

 vations should suflfice of itself to show that the phenomena of Jupiter's 

 cloud-laden atmosphere are not due to solar action. For the rift itself 

 continued, and the changes affecting 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 onward 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 respect to the surface of the planet below. 



' Two pictures of this belt, as seen March 12, 1860, and April 9, 1860, will be found 

 in my article on "Astronomy," in the "Encyclopaedia Britannica," vol. ii., p. 808. 



