Up till the year 1890 the rotation period of Venus was usually stated at twenty-three hours twenty-one minutes, or thereby, though this figure was only accepted with some hesitation, as in order to arrive at it there had to be some gentle squeezing of inconvenient observations. But in that year Schiaparelli announced that his observations were only consistent with a long period of rotation, which could not be less than six months, and was not greater than nine. The announcement naturally excited much discussion. Schiaparelli's views were strongly controverted, and for a time the astronomical world seemed to be almost equally divided in opinion. Gradually, however, the conclusion has come to be more and more accepted that Venus, like Mercury, rotates upon her axis in the same time as she takes to make her journey round the sun--in other words, that her day and her year are of the same length, amounting to about 225 of our days. In 1900 the controversy was to some extent reopened by the statement of the Russian astronomer Bélopolsky that his spectroscopic investigations pointed to a much more rapid rotation--to a period, indeed, considerably shorter than twenty-four hours. It is difficult, however, to reconcile this with the absence of polar flattening in the globe of Venus. Lowell's spectroscopic observations are stated by him to point to a period in accordance with his telescopic results--namely, 225 days. The matter can scarcely be regarded as settled in the meantime, but the balance of evidence seems in favour of the longer period.