第10章 THE PTOLEMAIC ERA(6)

Eratosthenes, again, contributed his mite to the treasure of human science--his one mite; and yet by that he is better known than by all the volumes which he seems to have poured out, on Ethics, Chronology, Criticism on the Old Attic Comedy, and what not, spun out of his weary brain during a long life of research and meditation. They have all perished,--like ninety-nine hundredths of the labours of that great literary age; and perhaps the world is no poorer for the loss. But one thing, which he attempted on a sound and practical philosophic method, stands, and will stand for ever. And after all, is not that enough to have lived for? to have found out one true thing, and, therefore, one imperishable thing, in one's life? If each one of us could but say when he died: "This one thing I have found out; this one thing I have proved to be possible; this one eternal fact I have rescued from Hela, the realm of the formless and unknown," how rich one such generation might make the world for ever!

But such is not the appointed method. The finders are few and far between, because the true seekers are few and far between; and a whole generation has often nothing to show for its existence but one solitary gem which some one man--often unnoticed in his time--has picked up for them, and so given them "a local habitation and a name."Eratosthenes had heard that in Syene, in Upper Egypt, deep wells were enlightened to the bottom on the day of the summer solstice, and that vertical objects cast no shadows.

He had before suggested, as is supposed, to Ptolemy Euergetes, to make him the two great copper armillae, or circles for determining the equinox, which stood for centuries in "that which is called the Square Porch"--probably somewhere in the Museum. By these he had calculated the obliquity of the ecliptic, closely enough to serve for a thousand years after. That was one work done. But what had the Syene shadows to do with that? Syene must be under that ecliptic. On the edge of it.

In short, just under the tropic. Now he had ascertained exactly the latitude of one place on the earth's surface. He had his known point from whence to start on a world-journey, and he would use it; he would calculate the circumference of the earth--and he did it. By observations made at Alexandria, he ascertained its latitude compared with that of Syene; and so ascertained what proportion to the whole circumference was borne by the 5000 stadia between Alexandria and Syene.

He fell into an error, by supposing Alexandria and Syene to be under the same meridians of longitude: but that did not prevent his arriving at a fair rough result of 252,000 stadia--31,500 Roman miles; considerably too much; but still, before him, I suppose, none knew whether it was 10,000, or 10,000,000. The right method having once been found, nothing remained but to employ it more accurately.

One other great merit of Eratosthenes is, that he first raised Geography to the rank of a science. His Geographica were an organic collection, the first the world had ever seen, of all the travels and books of earth-description heaped together in the Great Library, of which he was for many years the keeper. He began with a geognostic book, touched on the traces of Cataclysms and Change visible on the earth's surface;followed by two books, one a mathematical book, the other on political geography, and completed by a map--which one would like to see: but--not a trace of all remains, save a few quoted fragments -We are such stuff As dreams are made of.

But if Eratosthenes had hold of eternal fact and law on one point, there was a contemporary who had hold of it in more than one. I mean Archimedes; of whom, as I have said, we must speak as of an Alexandrian.

It was as a mechanician, rather than as an astronomer, that he gained his reputation. The stories of his Hydraulic Screw, the Great Ship which he built for Hiero, and launched by means of machinery, his crane, his war-engines, above all his somewhat mythical arrangement of mirrors, by which he set fire to ships in the harbour--all these, like the story of his detecting the alloy in Hiero's crown, while he himself was in the bath, and running home undressed shouting [Greek text: eureeka]--all these are schoolboys' tales. To the thoughtful person it is the method of the man which constitutes his real greatness, that power of insight by which he solved the two great problems of the nature of the lever and of hydrostatic pressure, which form the basis of all static and hydrostatic science to this day. And yet on that very question of the lever the great mind of Aristotle babbles--neither sees the thing itself, nor the way towards seeing it. But since Archimedes spoke, the thing seems self-evident to every schoolboy. There is something to me very solemn in such a fact as this. It brings us down to some of the very deepest questions of metaphysic. This mental insight of which we boast so much, what is it? Is it altogether a process of our own brain and will? If it be, why have so few the power, even among men of power, and they so seldom? If brain alone were what was wanted, what could not Aristotle have discovered? Or is it that no man can see a thing unless God shows it him? Is it that in each separate act of induction, that mysterious and transcendental process which cannot, let logicians try as they will, be expressed by any merely logical formula, Aristotelian or other--is it I say, that in each separate act of induction we do not find the law, but the law is shown to us, by Him who made the law?

Bacon thought so. Of that you may find clear proof in his writings.