92 THE POPULAR SCIENCE MONTHLY. 



differ less in velocity from the superincumbent atmosphere into which 

 they were driven than would masses expelled from higher latitudes. 

 (It is probable that the same explanation applies also in the case of 



the sun.) 



This conclusion, that the spots of Jupiter have rapid rates of rela- 

 tive motion, would of itself be of singular interest, especially when 

 we remember that the larger white spots represent masses of cloud 

 5 000 or 6,000 miles in diameter. Tljat such masses should be carried 

 along with velocities so enormous as to change their po'sitions rela- 

 tively to each other, at a rate sometimes of more than 150 miles per 

 hour, is a startling and stupendous fact. But it appears to me that the 

 fact is still more interesting in what it suggests than in what it reveals. 

 The movements taking place in the deep atmosphere of Jupiter are 

 very wonderful, but the cause of these movements is yet better wor- 

 thy of study. We cannot doubt that deep down below the visible 

 surface of the planet that is, the surface of its outermost cloud- 

 Ifiyerslies the fiery mass of the real planet. Outbursts, compared 

 with which the most tremendous volcanic explosions on our earth are 

 utterly insignificant, are continually taking place beneath the seem- 

 ingly quiescent envelope of the giant planet. Mighty currents carry 

 aloft great masses of heated vapor, which, as they force their way 

 through the upper and cooler strata of the atmosphere, are converted 

 into visible cloud. Currents of cool vapor descend toward the sur- 

 face, after assuming, no doubt, vorticose motions, and sweeping away 

 over wide areas the brighter cloud-masses, so as to form dark spots 

 on the disk of the planet. And, owing to the various depths to which 

 the different cloud-masses belong, and whence the up-rushing currents 

 of heated vapor have had their origin, horizontal currents of tremen- 

 dous velocity exist, by which the cloud-masses of one belt or of one 

 layer are hurried swiftly past the cloud-masses of a neighboring belt, 

 or of higher or low cloud-layers. The planet Jupiter, in fact, may 

 justly be described as a miniature sun, vastly inferior in bulk to our 

 own sun, inferior to a greater degree in heat, and in a greater degree 

 yet in lustre, but to be compared with the sun not with our earth in 

 size, in heat, and in lustx'e, and, lastly, in the tremendous energy of 

 the processes which are at work throughout his cloud-laden atmos- 

 pheric envelope. 



Since the above article was written, news has been received by 

 the Astronomical Society that Mr. Todd, a well-known observer of 

 Adelaide, New South Wales, has been able to trace the motions of 

 satellites behind the parts of the planet near the edge, or, in other 

 words, through those parts of the planet's atmosphere which have 

 hitherto been regarded as belonging to the mass of the planet itself. 



