Lecture I--The Ptolemaic Era

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But we must leave Archimedes for a man not perhaps so well known, but to whom we owe as much as to the great Syracusan--Hipparchus the astronomer. To his case much which I have just said applies. In him astronomic science seemed to awaken suddenly to a true inductive method, and after him to fall into its old slumber for 300 years. In the meantime Timocharis, Aristyllus, and Conon had each added their mites to the discoveries of Eratosthenes: but to Hipparchus we owe that theory of the heavens, commonly called the Ptolemaic system, which, starting from the assumption that the earth was the centre of the universe, attempted to explain the motions of the heavenly bodies by a complex system of supposed eccentrics and epicycles. This has of course now vanished before modern discoveries. But its value as a scientific attempt lies in this: that the method being a correct one, correct results were obtained, though starting from a false assumption; and Hipparchus and his successors were enabled by it to calculate and predict the changes of the heavens, in spite of their clumsy instruments, with almost as much accuracy as we do now.

For the purpose of working out this theory he required a science of trigonometry, plane and spherical: and this he accordingly seems to have invented. To him also we owe the discovery of that vast gradual change in the position of the fixed stars, in fact, of the whole celestial system, now known by the name of the precession of the equinoxes; the first great catalogue of fixed stars, to the number of 1080; attempts to ascertain whether the length of years and days were constant; with which, with his characteristic love of truth, he seems to have been hardly satisfied. He too invented the planisphere, or mode of representing the starry heavens upon a plane, and is the father of true geography, having formed the happy notion of mapping out the earth, as well as the heavens, by degrees of latitude and longitude.

Strange it is, and somewhat sad, that we should know nothing of this great man, should be hardly able to distinguish him from others of the same name, but through the works of a commentator, who wrote and observed in Alexandria 300 years after, during the age of the Antonines. I mean, of course, the famous Ptolemy, whose name so long bore the honour of that system which really belonged to Hipparchus.

This single fact speaks volumes for the real weakness of the great artificial school of literature and science founded by the kings of Egypt. From the father of Astronomy, as Delambre calls him, to Ptolemy, the first man who seems really to have appreciated him, we have not a discovery, hardly an observation or a name, to fill the gap. Physical sages there were; but they were geometers and mathematicians, rather than astronomic observers and inquirers. And in spite of all the huge appliances and advantages of that great Museum, its inhabitants were content, in physical science, as in all other branches of thought, to comment, to expound, to do everything but open their eyes and observe facts, and learn from them, as the predecessors whom they pretended to honour had done. But so it is always. A genius, an original man appears. He puts himself boldly in contact with facts, asks them what they mean, and writes down their answer for the world's use. And then his disciples must needs form a school, and a system; and fancy that they do honour to their master by refusing to follow in his steps; by making his book a fixed dogmatic canon; attaching to it some magical infallibility; declaring the very lie which he disproved by his whole existence, that discovery is henceforth impossible, and the sum of knowledge complete: instead of going on to discover as he discovered before them, and in following his method, show that they honour him, not in the letter, but in spirit and in truth.