742 THE POPULAR SCIENCE MONTHLY. 



other reasons it is not unlikely that some of his cloud formations may- 

 be more lasting than ours. That his gaseous envelope is, however, at 

 times subject to violent disturbances arising from a prodigious exer- 

 tion of internal forces is proved by instances of sudden changes in 

 the diameter of the disk. The Rev. T. W. Webb, in his " Celestial 

 Objects," mentions as "inexplicable" an observation of Smyth, con- 

 firmed by similar observations of Maclear and Pearson, all being at 

 different places, namely, that on June 26, 1828, Jupiter's second satel- 

 lite, after fairly entering upon the disk, in the course of its revolution, 

 was subsequently seen for four minutes outside it, and then suddenly 

 vanished. JVIore recently Secchi noticed a similar phenomenon ; and 

 the explanation can only be that Jupiter's atmosphere was suddenly 

 blown out for some thousands of miles and retreated again. Secchi 

 states that on April 2, 1874, he watched the first satellite as it was 

 about to cross the planet's disk, which appeared " finely undulated." 

 " When the satellite approached within its own diameter of the margin 

 of the planet the latter sprang toward it, appeared to touch it, and im- 

 mediately retired. This happened, backward and forward, until the 

 satellite had plainly entered upon the planet ; that is to say, for four 

 or five minutes.* . . o The satellite appeared fixed, and all the move- 

 ment seemed to belong to the disk of the planet." 



In October, 1879, Mr. Kidd, of Bramley, Guildford, saw, as is de- 

 scribed in the " Observatory " for November, the second satellite first 

 touch the disk, then appear separated from it, and finally pass behind 

 it, but remain for some time visible through it. The " Observatory " 

 for November also quotes the " Chicago Tribune," to the effect that 

 observations at the Dearborn Observatory indicate that changes in the 

 outline of the planet take place from day to day. Two sets of mea- 

 sures at the interval of a week are stated to have shown a difference 

 in the direction of the major axis amounting to 5°. 



When extensive belts or bright portions change rapidly, the storm- 

 effects must be immensely greater than in any of our hurricanes. 

 Jupiter's motion at the equator is at the rate of about 28,000 miles an 

 hour ; his daily rotation is completed in a few seconds less than ten 

 hours ; and objects in Jupiter weigh about two and a half times as 

 much as on our earth. When our winds move with a hurricane-speed 

 of 85 miles an hour, they exert a pressure upon whatever they strike 

 equal to 36 pounds per square foot. What, then, must be the force of 

 a Jovian storm, moving much heavier matter than our air, at the rate 

 of 300 miles an hour, as was observed on one occasion by Herschels ? 



On another occasion South saw a spot 22,000 miles long, and before 

 a friend who was present could commence a sketch it had nearly all 

 changed. There may in such cases be violent chemical action, a ter- 

 rific clashing together of atoms, and the precipitation of solid oxides 

 of metals, like the fumes produced by the burning of magnesium wire. 

 * "Comptes Eendus," 1874, vol. Ixxviii., p. 1468. 



