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 Phaëton: _Adde, quod assidua rapitur vertigine cœlum;_ _Nitor in adversum; nec me, qui cætera, 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.