1 on the Rotation of the Planets , See * % 2 i 
Obfervations on Jupiter in 1779. 
April 14. Clock 52" too late. 8 h. 48' A remarkable bright 
fpot in the equatorial belt towards the north is in the center, 
fee fig. 18. 
8 h. 58b The fpot is a little paft the center. 
April 19. Clock true meantime. 7I1. ioh There is a bright 
fpot juft nowin the center, which, from its fhape, I take to be 
the fame that was there April 1 4th. 
7 h. 20'. The fpot is vifibly paft the center. 
April 23. Clock (hews true time. 9 h. 38'. The fame bright 
fpot is in the center. 
9 h. 43k It is paft the center. Memorandum , my time- 
piece may be depended upon to a few feconds. 
It will not be amifs to obferve, that the fpots, as well as a 
great many other phenomena, were watched as they came on, 
paffed over the center, and went off the difk of Jupiter ; but I 
have only felefted thofe obfervations that were neceffary to my 
prefent purpofe. 
Comparing together the obfervations that were made in the 
year 1778, February 24th and March 3d, we obtain an interval 
of. 7 days 34 minutes, which being divided by 17 revolutions 
made by Jupiter on his axis, we have the time of one fynodicai 
revolution equal to 9 h. 54' 5 6 // ? 4. 
The dark fpot on February 25 was obferved fome time be* 
fore, and alfojuft after it was paft the center ; therefore I have 
fuppofed it to be in the center about 8 h. 5 8 / : and we have, 
R % February 
