SOME OF THE MARKINGS ON JUPITER. 5$ 



frequently presents the appearance of a huge uprising cliff. The 

 red spot was first noticed scientifically in 1878, when it was of a 

 dark red colour, as shown in Mr. N. E. Green's classical draw- 

 ings. It was surrounded by a bright halo-like substance, 

 probably a background, giving it a prominent aspect. It gradu- 

 ally faded year by year, and now it is very pale and of a greyish 

 tint ; indeed, in bad seeing it is often difficult of detection. The 

 inner portion of this remarkable oval spot is paler than the outer 

 portion, giving it a ring-like aspect. The following end is 

 somewhat darker, and has been seen connected with the bay 

 by a thin dark line. I have never been able to fairly detect that 

 line. This wonderful spot has been largely used in ascertaining 

 the rotation period of the planet. Dr. Marth, who is well known 

 as the constructor of tables of the varied aspects and motions of 

 Jupiter, has fixed the zero longitude of the planet at the 

 preceding end of the red spot, from whence, of course, the 

 longitudes of the different markings are calculated. The 

 movements of this spot are very slight. Possibly it is a fixture in 

 the Jovian atmosphere, and the slight movements are only 

 apparent, arising from the whitish material around it partly 

 covering it, and threatening to ultimately hide it from view. 

 What is it ? 



Here we may well pause, for the theories of its origin are too 

 numerous to detail. The writer inclines to the idea that it is 

 ejected matter from a lower atmospheric stratum floating in the 

 Jovian envelope, though something may be said for the theory 

 that it is a prominence based on the more solid portion of the 

 planet ; indeed, a huge mountain probably in a state of semi- 

 incandescence, the friction it would be subject to by the passing 

 currents of other material being sufficient to account for its heat, 

 for it should be takeii into account that the movements in the 

 Jovian atmosphere are at enormous rates. The diverse spots, 

 especially the darker ones, generally have a movement of their 

 own, as well as partaking of the general rotational motion. 

 Messrs. Stanley Williams and W. F. Denning, well-known and 

 highly-qualified observers of Jupiter, have paid special attention 



