186 
sometimes vary ; and that, in general, spots near the equator 
move more quickly than those in higher latitudes. 
The number of spots observed was seven, and they were 
denoted in the journal by the letters A, B, C, &c. ; but the 
observations of jive only were sufficiently numerous and exact 
to be available for the accurate determination of their periods 
of rotation. Tables are given showing the observed Green- 
wich mean times of meridional conjunction of the spots A, 
B, C, E, and F with the centre of the disc, corrected for the 
changes in the planet’s geocentric position and distance. 
The following values of the mean period are derived from the 
numbers in these tables : — 
h. 
m. 
S. 
s. 
From spot A, 
9 
55 
46.086 
± 
0.439 
55 55 ®5 
9 
55 
44.821 
± 
0.578 
c 
55 55 '-^5 
9 
55 
39.240 
± 
1.650 
E 
55 55 ■‘-'5 
9 
55 
37.812 
± 
0.636 
F 
55 55 ^5 
9 
55 
39.858 
± 
1.650 
Reference is then made to an interesting series of observa- 
tions of Jupiter, which had been kindly communicated to the 
Author by Sir William Keith Murray, Bart., of Ochtertyre, 
and which, though made without special reference to the 
question of rotation, had afforded the following mean periods 
of spots A and B : — 
h. m. s. s. 
A 9 55 45.96 ± 1.33 
B 9 55 43.62 ± 1.65 
A comparison of the differences between the periods of B, 
C, E, F, and that of A, and of their probable errors, fully 
confirms the conclusion drawn from former observations, that 
different spots have different periods of rotation. 
The observed distances between the spots A and B on 
eleven different nights are given, from which it appears that 
