Pliny the Elder (23-79 A.D.), in the encyclopedic work which he compiled under the title _Natural History_, drew freely on hundreds of Greek and Latin authors for his facts and fables. In the selection that he made from his sources can be traced, as in the work of Vitruvius and other Latin writers, the tendency to make the sciences subservient to the arts. For example, the one thousand species of plants of which he makes mention are considered from the medicinal or from the economic point of view. It was largely in the interest of their practical uses that the Roman regarded both plants and animals; his chief motive was not a disinterested love of truth. Pliny thought that each plant had its special virtue, and much of his botany is applied botany. So comprehensive a work as the _Natural History_ was sure to contain interesting anticipations of modern science. Pliny held that the earth hovers in the heavens upheld by the air, that its sphericity is proved by the fact that the mast of a ship approaching the land is visible before the hull comes in sight. He also taught that there are inhabitants on the other side of the earth (antipodes), that at the time of the winter solstice the polar night must last for twenty-four hours, and that the moon plays a part in the production of the tides. Nevertheless, the whole book is permeated by the idea that the purpose of nature is to minister to the needs of man. It further marks the practical spirit among the Romans that a work on agriculture by a Carthaginian (Mago) was translated by order of the Senate. Cato (234-149 B.C.), so characteristically Roman in his genius, wrote (_De Re Rustica_) concerning grains and the cultivation of fruits. Columella wrote treatises on agriculture and forestry. Among the technical writings of Varro besides the book on agriculture, which is extant, are numbered works on law, mensuration, and naval tactics.