314 PROCEEDINGS OP THE AMERICAN ACADEMY 



The gray band on which these black spots were formed underwent 

 very rapid clianges, afui on the following days new spots, similar to the 

 first, appeared, mostly in pairs, at irregular intervals on the following 

 side of the former, until at least one half of the whole circumference of 

 Jupiter was covered with round black spots, differing but little in size 

 and in depth of tint. 



Owing to the formation of these new spots, it was difficult to know 

 with certainty which was the one that had been observed before 

 passing the central meridian, and possibly errors may thus have 

 been made in mistaking one for the other, especially from the 28th of 

 October to the IGth of November. 



The following table gives the dates and times of the passages of the 

 preceding spot of the row across the central meridian. 



Great irregularities will be found in the apparent motion of this 

 mark, and possibly a different spot may have formed on the pre- 

 ceding side, thus producing a jump. This may have occurred between 

 the 8th and 10th of November, when the apparent motion was at the 

 rate of 27.5° ; i. e. this spot gained 27.5° a day on the red spot. The 

 mean period of rotation of the planet obtained from the observation 

 of 49 rotations of this mark equals 9*^ 47" G.10^ 



Mark H. 



On Nov. 19, the fifth or sixth spot from the preceding one became 

 considerably darker and more characteristic than the others, projecting 

 a little outside of the row on the north side. It was separated from 

 the next spot on the following side by a larger interval occupied by a 

 brilliant sort of bridge, strongly resembling some of the brilliant facuhe 

 which oftentimes separate sun-spots in activity. This facula-like 

 object, together with a sort of bright ring almost encircling it, gave to 

 that spot and the following one a very peculiar look, and bore a strik- 

 ing resemblance to some of the solar spots, which was very suggestive. 



In the beginning of December, some changes oocurre<l in these 

 spots, a long and narrow appendage being added to the preceiling one, 

 giving it the appearance of a tail preceding it to the southwest for a 

 distance three or four times its own diameter. 



On December 16, the black spots began to enlarge considerably, 

 while at the same time they became diffused on their border and much 



