306 PROCEEDINGS OF THE AMERICAN ACADEMY 



Although scattered observations were made on Feb. 12 and 13, 

 March 7 and 15, May 27, and June 13, no angular marking was 

 seen. On Sept. 8, however, the same mark reappeared, and remained 

 visible until the end of August, 1879. 



On Sept. 10, the angular marking seen on the 8th should have 

 been in sight, and within a few degrees of the central meridian, had 

 it followed its regular proper motion ; but it was not found on the 

 disk. West of the meridian, however, the step-like mark C was visible, 

 thus indicating that the angular mark was in the east very close to 

 the limb. In order to have been at that place, the marks C and D, 

 and perhaps the whole equatorial belt, must have moved backwards, 

 and retrograded in these two days some 75° or 80°. 



On the 25th of September, the great red spot was seen following 

 very closely the angular mark D, and both kept their relative dis- 

 tance until the disappearance of the latter in the following year. 



From the fact that this mark disappeared and re-appeared several 

 times, it may be supposed that it was hidden from sight by opaque 

 clouds or vapors floating high above it, and thus concealing it for 

 some time. But the great jump observed between the 8th and 1 0th 

 of September, 1878, shows that these markings, having no fixity at all, 

 are liable to be transported to great distances by the forces at work 

 on Jupiter, or to be destroyed and generated again afterwards ; only, 

 in the last case, it would seem singular that they should reappear in the 

 same form. 



The Great Red Spot, or ^Iark E. 



This curious and remarkable spot was seen by me for the first time 

 on Sept. 25, 1878. Since then, I have drawn it one huudred and 

 thirteen times in various positions upon the disk. 



In the following table will be found the dates and times of the jias- 

 sages of the centre or of either of the extremities of this spot on the 

 central meridian. 



It would have been desirable to give in this paper the longitudes of 

 the marks and spots at the time of their passage of the central 

 meridian, as thus their proper motion and irregularities might have 

 been easily ascertained. But as I had not an ephemeris at hand, giv- 

 ing the time when the assumed first meridian traversed the middle of 

 the disk, of an earlier date tiian that of Sept. 18, 1880, I have been 

 obliged to give the spots observed before that date without their cor- 

 responding longitudes. Those observed later, however, have th^ir 

 longitudes given in the last column, in which the daily rate of rota- 

 tion is assumed to be 870. G0°. 



