on the Rotation of the Planets , &c. 
I2J 
Obfervations on Jupiter in 1779. 
April 14. Clock 52'' too late. 8 h. 4s 7 A remarkable bright 
fpot in the equatorial belt towards the north is in the center, 
fee fig. 18. 
8 h. 5s 7 . The fpot is a little part the center. 
April 19. Clock true mean time. 7I1. io'. There is a bright 
fpot juft nowin the center, which, from its ftiape, I take to be' 
the fame that was there April 14th. 
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. 43'. 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 dilk 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 (ynodical 
revolution equal to 9 h. 54' 56", 4. 
The dark fpot on February 25 was obferved feme time be* 
fore, and alfojuft after it was paft the center; therefore I have 
fuppofed it to be in the center about 8 h. 58' : and we have. 
R 2 
February 
