Abstract
ON May 22 last, at 15h., I observed Jupiter through a 10-inch reflector, power 252, and saw the red spot between the east limb and centre of the planet. It was rather faint, and not nearly so conspicuous as some of the belts in its vicinity. According to careful estimation, the spot reached the central meridian of Jupiter at 15h. 35m. This is 15˙5 minutes before the time given in Mr. Marth's valuable “Ephemeris for Physical Observations of Jupiter,” published in the Monthly Notices for March 1890, p. 344. The difference proves that the motion of the spot continues to accelerate in a slight degree relatively to the mean rate of rotation of 9h. 55m. 40˙63s., adopted by Mr. Marth in his recent ephemerides. Observers, therefore, who wish to see the spot at mid-passage across the disk of Jupiter must turn their telescopes upon the planet at least a quarter of an hour before the predicted times based on the daily rate 870°˙27.
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