Corrections and clarifications

In the report "The drift of Saturn's north polar spot observed by the Hubble Space Telescope" by J. Caldwell et al. (16 Apr., p. 326), the revised System III rotation rate of the drift was incorrectly calculated. It should not have been "810.737 degrees +/- 0.008 degrees per day," as stated (line 21, col. 1, p. 329), but rather "810.851 degrees +/-0.008 degrees per day."