—xxiii. 281 [226].
The phases of Venus were first discovered by Galileo and were made known to the world, or rather to Kepler, in a mystic sentence which has often been quoted:—
“Hæc immatura, a me jam frustra leguntur—oy.”
“These things not ripe; at present [read] in vain [by others] are read by me.”
The former sentence transposed becomes—
Cynthiæ figuras æmulatur mater amorum.
The mother of loves [Venus] imitates the phases of Cynthia [the Moon].
Venus revolves round the Sun in 224½ days at a mean distance of about 67 millions of miles. Its apparent diameter varies between 9½″ in superior conjunction, and 62″ in inferior conjunction. The real diameter is about 7500 miles; in other words Venus is nearly as large as the Earth.
CHAPTER V.
THE EARTH.
To us, as its inhabitants, the Earth appeals in two characters, and in writing a book on astronomy it is necessary, yet difficult, to keep these two characters separate. The Earth is an ordinary planet member of the solar system, amenable to the same laws, impelled by the same forces, and going through the same movements as the other members of the Sun’s entourage. Yet, by reason of the fact that we are ourselves on the Earth and are not spectators of it looking at it from at a distance, there are many phenomena coming under our notice which require special treatment, and it is often very difficult to say where the province of the astronomer ends and that of the geographer begins. This volume being specially designed to deal with astronomical matters, I shall pass over many subjects which may be said to be on the border line, and which some of my readers may therefore be disappointed not to find discussed. Besides the geographer, the geologist and his scientific brother the mineralogist are concerned with the Earth regarded as a planet moving through space as the other planets do. The geologist studies the actual structure of the Earth, its circumstances and history so far as they have been revealed to us, whilst the mineralogist investigates and names the materials of which it is composed, and classifies such materials with the assistance of the geologist on the one hand and of the chemist on the other. All these subordinate sciences—subordinate I mean from an astronomer’s point of view—open up very varied, instructive, and interesting fields of study, but they are of course foreign to the purpose of the present volume.