M. Duval, who, if I mistake not, was librarian to the Emperor Francis I., gives us an account of the manner in which, in his childhood, pure instinct gave him the first ideas of astronomy. He was contemplating the moon which, as it declined towards the west, seemed to touch the trees of a wood. He doubted not that he should find it behind the trees, and, on running thither, was astonished to see it at the extremity of the horizon.

The following days his curiosity prompted him to watch the course of this luminary, and he was still more surprised to find that it rose and set at various hours. The different forms which it took from week to week, and its total disappearance for some nights, also contributed to fix his attention. All that a child could do was to observe and to admire, and this was doing much; not one in ten thousand has this curiosity and perseverance.

He studied, as he could, for three years, with no other book than the heavens, no other master than his eyes. He observed that the stars did not change their relative positions; but the brilliancy of the planet Venus having caught his attention, it seemed to him to have a particular course, like that of the moon. He watched it every night; it disappeared for a long time; and at length he saw it become the morning instead of the evening star. The course of the sun, which from month to month, rose and set in different parts of the heavens, did not escape him. He marked the solstices with two staves, without knowing what the solstices were.

It appears to me that some profit might be derived from this example, in teaching astronomy to a child of ten or twelve years of age, and with much greater facility than this extraordinary child, of whom I have spoken, taught himself its first elements.

It is a very attractive spectacle for a mind disposed to the contemplation of nature to see that the different phases of the moon are precisely the same as those of a globe round which a lighted candle is moved, showing here a quarter, here the half of its surface, and becoming invisible when an opaque body is interposed between it and the candle. In this manner it was that Galileo explained the true principles of astronomy before the doge and senators of Venice on St. Mark’s tower; he demonstrated everything to the eyes.

Indeed, not only a child, but even a man of mature age, who has seen the constellations only on maps or globes, finds it difficult to recognize them in the heavens. In a little time the child will quite well comprehend the causes of the sun’s apparent course, and the daily revolutions of the fixed stars.

He will, in particular, discover the constellations with the aid of these four Latin lines, made by an astronomer about fifty years ago, and which are not sufficiently known:

Delta Aries, Perseum Taurus, Geminique Capellam;

Nil Cancer, Plaustrum Leo, Virgo Coman, atque Bootem,

Libra Anguem, Anguiferum fert Scorpios; Antinoum Arcus;

Delphinum Caper, Amphora Equos, Cepheida Pisces.

Nothing should be said to him about the systems of Ptolemy and Tycho Brahe, because they are false; they can never be of any other service than to explain some passages in ancient authors, relating to the errors of antiquity. For instance, in the second book of Ovid’s “Metamorphoses,” the sun says to Pha?ton:

Adde, quod assidua rapitur vertigine c?lum;

Nitor in adversum; nec me, qui c?tera, vincit

Impetus; et rapido contrarius evehor orbi.

A rapid motion carries round the heavens;

But I— and I alone — resist its force,

Marching secure in my opposing path.

This idea of a first mover turning the heavens round in twenty-four hours with an impossible motion, and of the sun, though acted upon by this first motion, yet imperceptibly advancing from west to east by a motion peculiar to itself, and without a cause, would but embarrass a young beginner.

It is sufficient for him to know that, whether the earth revolves on its own axis and round the sun, or the sun completes his revolution in a year, appearances are nearly the same, and that, in astronomy, we are obliged to judge of things by our eyes before we examine them as natural philosophers.

He will soon know the cause of the eclipses of the sun and the moon, and why they do not occur every night. It will at first appear to him that, the moon being every month in opposition to and in conjunction with the sun, we should have an eclipse of the sun and one of the moon every month. But when he finds that these two luminaries are not in the same plane and are seldom in the same line with the earth, he will no longer be surprised.

He will easily be made to understand how it is that eclipses have been foretold, by knowing the exact circle in which the apparent motion of the sun and the real motion of the moon are accomplished. He will be told that observers found by experience and calculation the number of times that these two bodies are precisely in the same line with the earth in the space of nineteen years and a few hours, after which they seem to recommence the same course; so that, making the necessary allowances for the little inequalities that occurred during those nineteen years, the exact day, hour, and minute of an eclipse of the sun or moon were foretold. These first elements are soon acquired by a child of clear conceptions.

Not even the precession of th............