Did not the Greeks then do anything in the way of physical science that was to stand? Yes, there was a little work that was exact, and therefore lasting. Archimedes established the fundamental principle on the one hand of the lever, on the other of pressure in fluids--that is to say, laid the stable foundation of the sciences of statics and hydrostatics. Euclid developed, if he did not discover, the law of the reflection of light. Pythagoras discovered, and his followers developed, some of the fundamental principles of harmonics. Greater than any of the others in genuine scientific work was Hipparchus, who, with many erroneous theories, yet really laid the permanent foundation of the science of astronomy. Only one more name need be mentioned among the ancients--that of Ptolemy, who seemed possessed of a genuinely scientific spirit. He accomplished little original work, made no broad generalization (what is known as the Ptolemaic system was in reality the system of Hipparchus), but more than any other of the ancients he is the type of the true scientist in these respects--the accuracy of his observations, the thoroughness of his work at every point, and the really great additions that he made to science in the way of verifying, correcting, and extending the theory he received. He lived in the early part of the second century A. D. And the next name to attract our notice is that of Copernicus, more than twelve hundred years later. What is the meaning of that lapse of time? After such noble foundations had been laid, was there no great scientific work built thereon in all those centuries? Absolutely none. It will be well for us to think for a moment of what were the reasons for that barrenness, for the same causes are more or less at work at all times to hinder the growth of science and the extension of scientific method.