Spectroscopic Observations of the Rotation of Saturn

Our present information concerning the rotation of Saturn has been derived from observations of the few spots that have been seen at rare intervals on the planet's disk. One of these appearing in the equatorial region in 1876 was followed for several weeks by Asaph Hall,1 its discoverer, who obtained a rotational period of 10 hours 14.4 minutes, while several such spots observed by A. Stanley Williams2 in the years 1891 to 1894 yielded periods between 10 hours 12.6 minutes and 10 hours 14.3 minutes. The bright equatorial spot of 1933, which was followed by a number of observers seemed to conform to Hall's period within the error of observation.8 Only on two occasions have planetary details of this character at higher latitudes been studied and these have given a period of rotation nearly 4 per cent longer than that found in regions near the equator. Thus a spot in 36° north latitude discovered by Barnard4 in 1903 was shown by him to make one revolution in 10 hours and 38 minutes and one observed in similar south lati-