_Observations of Schröter and Sir W. Herschel._—Schröter observed Mercury with characteristic diligence between 1780 and 1815. In 1800 he several times remarked that the southern horn of the crescent was blunted, and fixed the planet’s rotation-period at 24^h 4^m. He also inferred the existence of a mountain 12 miles in height. But elements of doubt are attached to some of Schröter’s observations; and Sir W. Herschel, whose telescopic surveys of both Mercury and Venus were singularly barren of interesting results, pointed out their improbability. But the great observer of Slough was not very amicably disposed towards his rival in Germany. His strictures appear, however, to have been not without justice if we consider them in the light of modern observations. _Surface-markings._—Spots or markings of any kind have rarely been distinguished on Mercury. On June 11, 1867, Prince recorded a bright spot, with faint lines diverging from it N.E. and S. The spot was a little S. of the centre. Birmingham, on March 13, 1870, glimpsed a large white spot near the planet’s E. limb, and Vögel, at Bothkamp, observed spots on April 14 and 22, 1871. These instances are quoted by Webb, and they, in combination with the markings seen by Schiaparelli at Milan and by the author at Bristol in 1882, sufficiently attest that this object deserves more attentive study. [Illustration: Fig. 29. 1882 Nov. 5, 18^h 49^m. 1882, Nov. 6, 18^h 55^m. Mercury as a morning star. (10-inch Reflector; power 212.)] Amateurs with moderately large instruments would be usefully employed in following this planet at the most opportune periods and making careful drawings under the highest powers that can be successfully applied. Mercury has been persistently neglected by many in past years, and no doubt this “swift-winged messenger of the Gods” has eluded some of his would-be pursuers; but there is every prospect that a patient observer, careful to utilize all available opportunities, would soon gather some profitable data relating to his appearance. _Transits of Mercury._—One of the most interesting phenomena, albeit a somewhat rare event, in connection with Mercury, is that of a transit across the Sun. The planet then appears as a black circular spot. Observers have noticed one or two very small luminous points on the black disk, and an annulus has been visible round it. These features are probably optical effects, and it will be worth while to remember them on the occasion of future transits, of which the subjoined is a list:— 1891, May 9. 1894, Nov. 10. 1907, Nov. 12. 1914, Nov. 6. 1924, May 7. 1927, Nov. 8. 1937, May 10. 1940, Nov. 12. 1953, Nov. 13. 1960, Nov. 6. 1970, May 9. 1973, Nov. 9. The first observer of a transit of Mercury appears to have been Gassendi, at Paris, on Nov. 7, 1631.