After the time of Schröter there was no astronomer who paid much attention to either Mercury or Venus until the arrival on the scene of the most persistent planetary observer and one of the foremost astronomers of the nineteenth century. _Giovanni Virginio Schiaparelli_ was born at Savigliano, in Piedmont, in 1835, and graduated at Turin in 1854. Called to Milan as assistant in the Brera Observatory in 1860, he became director in 1862, and there for thirty-eight years he studied astronomy in all its aspects, making a great name for himself in various branches of the science. In 1900 he retired from the post of director, and pursues his astronomical researches in his retirement. In 1882 Schiaparelli took up the study of Mercury in the clear air of Milan. Instead of observing the planet through the evening haze, like Schröter and others, he examined it by day, and was enabled to follow it hourly instead of looking at it for a short period when near the horizon. At length, after seven years’ observation, he announced, on December 8, 1889, that Mercury performs only one rotation during its revolution round the Sun—in fact, that its day and year coincide. As a consequence, the planet keeps the same face towards the Sun, one side having everlasting day and the other perpetual night; but owing to the libratory movement of Mercury—the result of uniform motion on its axis and irregular motion in its orbit—the Sun rises and sets on a small zone of the planet’s surface. Schiaparelli’s observations indicated that Mercury is a much spotted globe, with a moderately dense atmosphere, and he was enabled to form a chart of its surface-markings. Schiaparelli’s conclusions remained until 1896 unconfirmed and yet not denied, although most astronomers were sceptical on the subject. In 1896 the subject was taken up by the American astronomer, _Percival Lowell_ (born 1855), who, in the clear air of Arizona, confirmed Schiaparelli’s conclusions, fixing 88 days as the period of rotation. He remarked, however, that no signs of an atmosphere or clouds were visible to him. The surface of Mercury, he says, is colourless,—“a geography in black and white.” The determination of the rotation period by Schiaparelli and Lowell is now generally accepted, and is confirmed by the theory of tidal friction. It is only right to add that _William Frederick Denning_ (born 1848) in 1881 suspected a rotation period of 25 hours, but this remains unconfirmed. In April 1871 the spectrum of Mercury was examined by _Hermann Carl Vogel_ (born 1842) at Bothkamp. He suspected traces of an atmosphere similar to ours, but was not certain. Of more interest are the photometric observations of Zöllner in 1874. These observations indicated that the surface of Mercury is rugged and mountainous, and comparable with the Moon,—a conclusion supported by Lowell’s observations in 1896.