318 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Mark L. 



Soon after the gray band K, above described, had disappeared, some 

 changes occurred in the markings of that particular region of Jupiter. 

 On Nov. 15, a large oval gray spot, resembling the red spot in size and 

 in shape, made its appearance at the same jjlace which the gray band 

 had occupied. On its southern side this oval spot was edged with a 

 narrow bright border, which made it appear more sharply defined on 

 that side. This oblong spot has been carefully observed, and was lost 

 in the beginning of February. 



The following are the dates and times of the passages of the centre 

 of this spot on the central meridian. 



It is doubtful whether the observation of Feb. 2 relates to the 

 same marking as that last seen on Jan. 22, although the object 

 appeared exactly like it in form and in size. On Jan. 31, at 5^ 38", 

 a dark oval spot was seen on the east limb ; undoubtedly this was the 

 same object seen on the 22d, and no other sjiot was to be seen towards 

 the west, or at any other place. If the spot observed on Feb. 2 

 had then existed, it would have been less than 2** 30"" distant from and 

 preceding the first, and therefore visible west of the centre of the disk. 

 The spot observed on the 2d, then, must have been either the old one, 

 having made a jump of 118® in two days, or a new form, which 

 appeared between the 31st of January and the 2d of February. It 

 seems probable that the last supposition is the true one. 



The apparent proper motion of tlie spot K has in general been slow 

 and irregular, being sometimes retrograde. If, however, we take its 

 position when first observed on Nov. 15, and that of Jan. 22, when it 

 was last seen, we have a diflTerence of nearly 29° for its direct motion 

 during this interval. 



The rotation of Jupiter derived from the observation of tliis mark 

 would be 9" 55*" 14 60". 



Below is a table giving the approximate period of rotation which we 

 would give to Jupiter if it were determined from the observations of the 



