OP ARTS AND SCIENCES. 



303 



The mean period of rotation given by mark C, as obtained from 

 567 rotations, from April 11 to Dec. 2, equals 35,740.5' or 9^ 55" 40.5'. 

 By taking the whole period of observations from April 11, 1877, to 

 Sept. 10, 1878, we have 1,249 rotations, the mean of which is over 

 four seconds and a half less, or 9^ 55™ 35. 9^ 



Mark D. 



Another permanent and characteristic marking was also observed 

 in 1877 on the southern border of the equatorial belt, following the 

 step-like mark C, above described, at a distance of about 80 or 85 

 degrees. This mark was of an angular form produced on the preceding 

 side by the straight border line of the broader part of the equatorial 

 belt, and the sloping curved line joining the broadest to the narrowest 

 portion of this belt on the following side. 



This angular mark, observed first on April 14, continued visible 

 throughout the year 1877, and was seen as late as Nov. 6, when the 

 observations were discontinued, owing to the proximity of Jupiter 

 to the Sun. It was found again in 1878, on Sept. 8, when I re- 

 sumed my regular observations ; and it continued to be seen through 

 that year, and also in 1879, until the end of August, when it slowly 

 disappeared, the equatorial belt then resuming its usual uniform width 

 throughout. 



It is impossible from my observations to know the exact time of 

 the first appearance of this mark, but it is certain that it was not 

 once seen in 1876 from the end of March to the 19th of October, 

 although the planet was observed and drawn one hundred and twenty- 

 five times during this interval. 



