8 



There is, for instance, a well-defined break or hollow in the 

 northern dark belt, which at first preceded the spot by some 

 20m., but which, on the 23rd, was considerably to the east of 

 the spot. It is a noticeable fact that both the white spots and 

 this dusky spot are on the light equatorial belt, and there are 

 also one or two fainter markings on this belt that seem to keep 

 their position relative to the dusky spot. It thus appears that 

 the surface on the equatorial bright belt moves round faster, at 

 the rate of about 2,000 miles per Jovian day, than the portions 

 connected with the darker belts to the north and south of the 

 equator. This extremely interesting hypothesis has been often 

 previously stated. 



It will be well in conclusion to take a rapid glance at the 

 general physical appearance of Jupiter's surface at the present 

 time. All round the north pole, extending to about latitude 

 45°, is a dark grey shading, which seems to defy the resolving 

 power of even the largest and best telescopes. At times, with 

 an unusually good definition, it presents a streaky appearance, 

 and seems to consist of innumerable very fine lines parallel to 

 the equator. South of the shading to about latitude 10° to 15° 

 !N. the planet's surface is of a white or very faint yellowish 

 colour, broken by two dark bands encircling the planet in 

 about latitude 23° and 25°. At 10° or 15° N. is the northern 

 edge of the north dark belt. This is by far the most irregular 

 belt or band on the planet. It is roughly parallel to the 

 equator — as, in fact, are all the belts — but on either edge are 

 protuberances, hollows, knots, breaks, &c, while the interior is 

 constantly exhibiting white patches or streaks, looking like 

 masses of white cloud. The northern edge is usually well 

 defined, but the southern gradually merges into the equatorial 

 bright belt. This belt is, perhaps, the most beautiful portion 

 of the planet. Its general appearance, without critical 

 examination, is that of a light reddish band round the centre 

 of the planet, darker on the north than on the south side, and 

 with a number of white-looking patches, somewhat like a bank 

 of cumulus cloud resting on the dark belt bounding its southern 

 extremity. On more careful examination it will be noticed 

 that there are a series of festoons, some regular, but for the 

 most part of a somewhat irregular formation, the tops of the 

 arches making awa-vyline along the equator; while the pillars 

 of the festoons extend downwards to the south dark belt, 

 which very often forms a protuberance to meet them. It is 

 very likely, I think, that the white patches inside of these fes- 

 toons, which are constantly changing, have given rise to the 

 irregular rotation periods that have been quite recently deduced 

 for Jupiter's equatorial regions ; and the most interesting 

 questions for the present Jovian season will centre in the 



