Perhaps this defect of thought, this lack of personality towards facts, is most strikingly perceived in the slowness with which most primary ideas of the form and motion of the earth made their way among men. Although astronomy is the oldest of sciences, and the only one progressive science of antiquity; and although the idea that the earth was a sphere, was one of the earliest in Greek philosophy; yet this same Lactantius in the 4th century is vehemently arguing as follows: "Is it possible that men can be so absurd as to believe that the crops and trees on the other side of the earth hang downwards, and that men there have their feet higher than their heads? If you ask of them how they defend these monstrosities--how things do not fall away from the earth on that side? they reply that the nature of things is such that heavy bodies tend towards the centre, like the spokes of a wheel, while light bodies, as clouds, smoke, fire, tend from the earth towards the heavens on all sides. Now I am really at a loss what to say of those who, when they have once gone wrong, steadily persevere in their folly and defend one absurd opinion by another." And coming on down to the eighth century, the anecdote is well known of honest Bishop Virgil of Salisbury, who shocked some of his contemporaries by his belief in the real existence of the antipodes, to such an extent that many thought he should be censured by the Pope for an opinion which involved the existence of a whole "world of human beings out of reach of the conditions of salvation." And finally we all know the tribulations of Columbus on this point far down in the fifteenth century, at the very beginning of the Renaissance. Now this infirmity of mind is as I said, not distinctive of the Greek. To me it seems simply a natural incident of the youth of reason, of the childhood of personality. At any rate, for a dozen centuries and more after Aristotle's death, to study science, means to study Aristotle; in vain do we hear Roger Bacon in the thirteenth century--that prophet philosopher who first announces the two rallying cries of modern science, mathematics and experiment--in vain do we hear Roger Bacon crying: "If I had power over the works of Aristotle I would have them all burnt; for it is only a loss of time, a course of error, and a multiplication of ignorance beyond expression, to study them."