194 MR, JOSEPH BAXENDELL ON 



XII. — On the Rotation of Jupiter. 

 By Joseph Baxendell, F.R.A.S. 



Eead before the Physical and Mathematical Section, 

 December 8th, 1859. 



During the last winter and spring I availed myself of the 

 opportunity presented by the appearance of several small 

 isolated dark spots on the surface of Jupiter to make a 

 series of observations with the ultimate view of obtaining 

 a re-determination of this planet^s period of rotation; and 

 with the more immediate object of testing the conclusions 

 which have been drawn from the observations of Cassini, 

 Maraldi, Sir William Herschel, Schroeter, &c., to the 

 effect that different spots have different periods of rota- 

 tion ; that the time of rotation of the same spot will some- 

 times vary ; and that in general spots near the equator 

 move more quickly than those in higher latitudes. 



Some of the observations were made at my own house 

 with a Newtonian reflector of seven inches aperture and 

 eighty inches focal length ; but the greater number were 

 made at Mr. Worthington^s observatory with his excellent 

 equatorially-mounted achromatic of five inches aperture 

 and seventy inches focal length, and Newtonian reflector 

 of thirteen inches aperture and nine feet focal length. The 

 magnifying powers employed in making the estimations 

 of the spots ranged, according to atmospherical circum- 

 stances, from 130 to 301, those most frequently used 

 being 180 and 223. 



