3 



was a total change of the whole structure of the belts in that 

 vicinity and the formation of an elliptic cloud-like mass, 

 separate from the general contour of the belts. This cloud 

 was almost a perfect oval in shape, and was pre-eminently 

 rose-tinted. But the most remarkable phase of all was the 

 rapid proper motion of this 'elliptical cloud.' I watched it for 

 nearly an hour, and in that time its front moved on the disc of 

 the planet about one-fourth of the planet's diameter. It passed 

 by the most easterly of the spots, and its front had reached to 

 the most westerly spot, and was passing it at 12h. 5m., Grl.M.T." 

 These remarks of Professor Pritchett were not written until 

 November, 1878, and meanwhile other observers had noticed 

 this spot. Mr. F. C. Dennett first saw it on July 27, and 

 makes the following remarks re its proper motion : — "Between 

 July 27, 13, and November 11, 5.5, the longitude of its 

 preceding extremity seems to have increased some 24°, which 

 means a proper motion eastward of more than 230 miles per 

 day. But that is not all. At 6h. 5m., October 25, the oval 

 patch was well elevated in the south temperate zone, whilst on 

 November 11, 5.5, it had seemingly 'pushed' the equatorial 

 belt some 8,000 miles nearer the equator." The next that seems 

 to have been heard about this spot was from a letter written 

 to the "Observatory" of April 1, 1879, by Mr. E. Leopold 

 Trouvelot, of Cambridge, U.S.A., dated January 20, 1879. He 

 observed it for the first time on September 25, 1878, at 6.30, 

 C.M.T., and in his letter draws attention to the fact that it is 

 apparently periodic in its visibility. He thinks, however, that 

 this may not have been the identical spot seen on July 9 by 

 Professor Pritchett, although it occupied almost exactly the 

 same position ; for Professor Pritchett failed to see it on July 

 10 and 15, when it should have been visible if it existed ; and 

 Mr. Trouvelot also failed to see the spot on September 6, 10, 15, 

 20, and 22, when Jupiter presented the same region to the ob- 

 server. (AVe must not forget, though, that Mr. Dennett ob- 

 served the spot on July 27.) Mr. Trouvelot further says: — 

 " Between September 19 and 20 considerable changes occurred 

 in the markings of the planet, the southern border of the 

 equatorial belt assuming at one point a very characteristic 

 angular form, which on the 25th was recognised on the west of 

 the red spot, and quite close to it. If the red spot had existed 

 on the 20th it is impossible that it should have escaped 

 notice, as the atmospheric condition was very fine on that 

 night, and a good drawing of Jupiter was obtained. It seems 

 certain, therefore, that this spot formed between the 22nd and 

 25th of September, as it was not seen on the 22nd at 7h., 

 C.M.T. It is very remarkable that this spot appeared precisely 

 at the same place, or, at least, very nearly so, where a similar 



