Sir W. Herschel frequently examined this planet between 1777 and 1793, but could not discern spots sufficiently definite and durable to enable him to fix the time of rotation. He dissented from Schröter as to the alleged mountains, and said, “No eye which is not considerably better than mine, or assisted by much better telescopes, will ever get a sight of them.” Mädler effected some observations of this planet in 1833 and some subsequent years. He detected spots on two occasions only, but noticed irregularities in the terminator and cusps. Di Vico and others at Rome, in 1840-1, devoted much attention to this object, and secured a large number of observations. They appear to have recovered the spots charted by Bianchini, and described them as of the last degree of faintness. The observers who saw the spots most readily were those who had the most difficulty in detecting the faint companion of a close double star. In the spring of 1841 Di Vico saw a marking on the northern cusp involved in an oval luminosity, and he likened it to a crater on the Moon viewed obliquely. This spot had a diameter of at least 4½″, and it was seen to advance even into the obscure part of the disk. _Rotation-Period._—The following are the periods of rotation as given by the different authorities whose observations we have mentioned:— 1666-7. Cassini 23 hrs. 21 min. 1726-8. Bianchini 24 days 8 hrs.[28] 1811. Schröter 23 hrs. 21 min. 8 sec.[29] 1840-1. Di Vico 23 hrs. 21 min. 22 sec. Schiaparelli has recently discussed a large number of observations of this planet, and concludes that, like Mercury, she rotates on her axis in the same time that she completes a sidereal revolution round the Sun, viz. in 224·7 days! I merely mention this remarkable deduction, without quoting any facts in opposition to it. From observations by Perrotin at Nice in 1890, including 74 observations, the rotation of this planet is very slow, and is made in such a way that the relative positions of the spots and terminator do not experience any notable change during many days. [Illustration: Fig. 30. 1881, Mar. 22, 6^h. 1881, Mar. 26, 7^h. 1881, Mar. 28, 6½^h. Venus as an evening star. (10-inch Reflector; power 212.)]