There was a second thing that cramped the Greek mind, the institution of domestic slavery. Slavery was implicit in Greek life; men could conceive of neither comfort nor dignity without it. But slavery shuts off one’s sympathy not only from a class of one’s fellow subjects; it puts the slave-owner into a class and organization against all stranger men. One is of an elect tribe. Plato, carried by his clear reason and the noble sanity of his spirit beyond the things of the present, would have abolished slavery; much popular feeling and the New Comedy were against it; the Stoics and Epicureans, many of whom were slaves, condemned it as unnatural, but finding it too strong to upset, decided that it did not affect the soul and might be ignored. With the wise there was no bound or free. To the matter-of-fact Aristotle, and probably to most practical men, its abolition was inconceivable. So they declared that there were in the world men “naturally slaves.”... Finally, the thought of the Greeks was hampered by a want of knowledge that is almost inconceivable to us to-day. They had no knowledge of the past of mankind at all; at best they had a few shrewd guesses. They had no knowledge of geography beyond the range of the Mediterranean basin and the frontiers of Persia. We know far more to-day of what was going on in Susa, Persepolis, Babylon, and Memphis in the time of Pericles than he did. Their astronomical ideas were still in the state of rudimentary speculations. Anaxagoras, greatly daring, thought the sun and moon were vast globes, so vast that the sun was probably “as big as all the Peloponnesus.” The forty-seventh proposition of the first book of Euclid was regarded as one of the supreme triumphs of the human mind. Their ideas in physics and chemistry were the results of profound cogitation; it is wonderful that they did guess at atomic structure. One has to remember their extraordinary poverty in the matter of experimental apparatus. They had coloured glass for ornament, but no white glass; no accurate means of measuring the minor intervals of time, no really efficient numerical notation, no very accurate scales, no rudiments of telescope or microscope. A modern scientific man dumped down in the Athens of Pericles would have found the utmost difficulty in demonstrating the elements of his knowledge, however crudely, to the men he would have found there. He would have had to rig up the simplest apparatus under every disadvantage, while Socrates pointed out the absurdity of seeking Truth with pieces of wood and string and metal such as small boys use for fishing. And our professor of science would also have been in constant danger of a prosecution for impiety.