Page:Popular Science Monthly Volume 9.djvu/467

Rh not altogether escape his means of observation. "It appears," he cautiously observes, "as if the pole-star had a motion [round the pole] like the rest of the stars."

Again, is it not amazing that for thousands of years mankind should have been in presence of so frequent a phenomenon as the zodiacal light—a phenomenon which in southern latitudes is specially impressive—without considering it to be worthy of mention, or rather, let us say, without seeing it, until Childrey, in the middle of the seventeenth century, discovered it, if we may so speak? So, too, may it excite our wonder, to think that the earliest definite mention of the noteworthy phenomena (easily visible with the naked eye) attending a total eclipse of the sun dates only from the year 1706, that is to say, a period of time full one hundred years subsequent to the invention of the telescope.

Thus the ancients were deficient in even the most elementary powers of observation. The simple but truthful noting of what is perceived by the senses is the prerogative of our time. But what of the restless spirit of speculation with which Schiller taxes the ancients?

Here permit me to recall anew to your memories, by an instance taken from the history of astronomy, thoughts which oftentimes, perhaps, have occurred to us all. Plutarch's dialogue on "The Visage that is seen in the Moon's Disk" has ever been regarded as containing the sum and substance of all man's notions and knowledge of our satellite down to the period when it was written. The very title is provocative of mirth to us, the children of the modern time. The Visage in the Moon! Nowadays it only suggests to the poet and the artist satirical ideas: in olden times it was the starting-point of profound meditations, which were held not to be unworthy of being attributed to the most famous philosophers and mathematicians of the day. The author first in all earnestness demonstrates the absurdity of the opinion which asserts the figure appearing in the moon to be nothing else but an optical illusion arising from the visual sense being dazzled by the brightness of the moon's disk. Next we have a lengthy refutation of another opinion, which says that the visage in the moon is the reflection of our ocean. Among other reasons given to show the erroneousness of this opinion is this, that there is only one ocean, and that, if the visage in the moon were a reflection of it, then the ocean must be made up of parts separated from one another by isthmuses and continents! The third opinion combated by Plutarch is to the effect that the moon is a mixture of air and of a mild kind of fire; as sometimes during a perfect calm the surface of a body of water becomes ruffled—a thing itself to be demonstrated—so too does the air assume a blackish color: thus is explained the appearance as of a human face in the moon. The hypothesis of the Stoics, who affirmed the moon to be a globe of fire, on the surface of which rests