187 
the distance was greater on January 18th and March 1 0th 
than on December 20th and February 2nd; and as the pro- 
bable error of the mean period of B, derived both from the 
Author’s and Sir William Keith Murray’s observations, is 
greater than that of A, it is inferred that the changes in the 
distance between the spots were principally due to irregu- 
larities in the motion of B. It is also shown from a com- 
parison of the Author’s observations of F with Sir William 
Keith Murray’s, that the motion of this spot was also 
irregular. 
Adopting the position of the axis of rotation of Jupiter 
given in the Introduction to Damoiseau’s “ Tables Eclip- 
tiques des Satellites de Jupiter” the mean result of three 
nights’ micrometrical measures gives the latitude of spot A = 
13° 47' south; and the mean deduced from fourteen of Sir 
William Keith Murray’s diagrams is 13° 11'. The spots B, 
C, and F were all very nearly on the parallel of A, while E, 
the spot which had the shortest period of rotation, was in 
latitude 28^° south. It appears, therefore, that the con- 
clusion drawn by Cassini from his own observations, that 
spots near the equator generally move more quickly than 
those in higher latitudes, receives no support from the obser- 
vations discussed in this Paper. 
The Author remarks that his results afford no certain in- 
formation respecting the period of rotation of the planet 
itself, as distinguished from that of its spots, and he considers 
that in the present state of our knowledge of the phenomena 
which take place on its surface, or in its atmosphere, any 
conclusion as to its exact period of rotation, based upon 
observations of the times of rotation of its spots, must neces- 
sarily be very precarious. 
A Paper was also read by Mr. Thomas Caiuiick, “ On 
the Sun’s Orbit Plane.” 
Starting with the assumption that the rotation of the 
