ECLIPSES OF JUPITER'S SATELLITES.—In Harvard Circular No. 198 Prof. E. C. Pickering directs attention to the need for continued observations of the eclipses of Jupiter's satellites. He points out that the observations are easy and interesting, and such as can readily be undertaken by amateurs. While the probable error of a photometric determination of the time of an eclipse is about 2 seconds, the average deviation from the time computed by the tables of Prof. Sampson is about 7 seconds. These deviations appear to be real, and a possible explanation is that the apparent diameter of the planet, and therefore of its shadow, varies with the cloudiness of the Jovian atmosphere. Several independent observations tending to confirm large deviations from theory would thus be valuable.