De Opificio Mundi

The planets too, and the corresponding host of fixed stars, are arrayed in seven divisions, displaying a very great sympathy with the air and the earth. For they turn the air towards the times, that are called the seasons of the year, causing in each of them innumerable changes by calm weather, and pleasant breezes, and clouds, and irresistible blasts of wind. And again, they make rivers to overflow and to subside, and turn plains into lakes; and again, on the contrary, they dry up the waters: they also cause the alterations of the seas, when they recede, and return with a reflux. For at times, when the tide recedes on a sudden, an extensive line of shore occupies what is usually a wide gulf of sea; and in a short time afterwards, the waters are brought back, and there appears a sea, sailed over, not by shallow boats, but by ships of exceeding great burden.

And they also give increase and perfection to all the terrestrial animals and plants which produce fruit, endowing each with a nature to last a long time, so that new plants may flourish and come to maturity; —the old ones having passed away, in order to provide an abundant supply of necessary things.

Moreover, the constellation Ursa Major, which men call the guide of mariners, consists of seven stars, which the pilots keeping in view, steer in innumerable paths across the sea, directing their endeavours towards an incredible task, beyond the capacity of human intellect. For it is through conjectures, directed by the aforementioned stars, that they have discovered countries which were previously unknown; those who dwell on the continent having discovered islands, and islanders having found out continents. For it was fitting that the recesses both of earth and sea should be revealed to that God-loving animal, the race of mankind, by the purest of essences, namely heaven.

And besides the stars above mentioned the band of the Pleiades is also made up of seven stars, the rising and occultation of which are the causes of great benefits to all men. For when they set, the furrows are ploughed up for the purpose of sowing; and when they are about to rise, they bring glad tidings of harvest; and after they have arisen, they awaken the rejoicing husbandman to the collection of their necessary food. And they with joy store up their food for their daily use.

And the sun, the ruler of the day, making two equinoxes