THE ROTATION OF JUPITER. 199 



October, according to Sir William Keith Murray's obser- 

 vations, it followed A ih. ^^'^m. ; ou the 12th November, 

 a tolerably good observation of my own gave precisely the 

 same difference ; but on the 2^th January the distance 

 had diminished to ih. 41 •4m., and on the 2nd February 

 it was only ih. o^i'jm. 



Adopting the position of the axis of rotation of Jupiter 

 given in the introduction to Damoiseau's Tables Ecliptiques 

 des Satellites de Jupiter, the mean result of three nights' 

 micrometrical measures gives the latitude of spot A=i3° 

 47' south; and the mean deduced from fourteen of Sir 

 William Keith Murray's diagrams is 13° 11' S. 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 about 28^° S. It appears, therefore, that 

 the conclusion drawn by Cassini, from his own observa- 

 tions, that spots near the equator of the planet generally 

 move quicker than those in higher latitudes, receives no 

 support from these observations. 



It is hardly necessary to remark that the results now 

 given aflFord no certain information as to the period of 

 rotation of the planet itself, as distinguished from that 

 of its spots. On the contrary they seem to me to indicate 

 very clearly — especially when taken in connexion with 

 the results obtained by former observers — that in the 

 present state of our knowledge of the phenomena which 

 take place on the surface of the planet or in its atmo- 

 sphere, any conclusion as to its exact period of rotation 

 based upon observations of the times of rotation of its 

 spots must necessarily be very precarious. 



