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:—

The first observer of a transit of Mercury appears to have been Gassendi, at Paris, on Nov. 7, 1631.

Occultations of Mercury.—There was an occultation of Mercury by the Moon on April 25, 1838. It occurred on the day of the planet’s greatest elongation E., and at a time in the evening when it might have been most suitably witnessed, but cloudy skies appear to have frustrated the hopes of intending observers. There was a repetition of the event on the morning of May 2, 1867, and it occurred, curiously enough, less than 24 hours after an occultation of Venus.

[CHAPTER VIII.]
VENUS.

Beauty of Venus.—Brilliancy.—Period &c.—Venus as a telescopic object.—Surface-markings on the planet.—Rotation-period.—Faintness of the markings.—Twilight on Venus.—Alleged Satellite.—Further observations required.—Transits of Venus.—Occultations of Venus.

“Friend to mankind, she glitters from afar,—

Now the bright evening, now the morning star.”