Page:Popular Science Monthly Volume 70.djvu/421

Rh because the people would have no place to go when it began to decrease. What an immense amount of speculation and calculation the Ptolemaic system made for the astronomers! The philosophers all agreed with Pliny that 'with the mind we see, with the mind we discriminate'; but unfortunately they too often forgot that the mind can not discriminate unless the senses have correctly furnished the facts. So far as sight is concerned, this is strikingly exemplified in all the work of the well-known mathematician, Euclid. As he knew nothing about refraction and had no rational theory of light, he had recourse to philosophy to provide him with a basis for his work on optics, but which is really a treatise on perspective. So far as is now known, the first man who made a study of refraction was Posidonius, who lived nearly two centuries after the father of geometry. He illustrated the principle by the familiar experiment of placing a coin on the bottom of an empty vessel in such a way that it was not visible because of the intervening rim, then bringing it into sight by filling the vessel with water.

The ancients were almost entirely without apparatus and had no instruments of precision; in fact, very few of them had any interest in the mechanic arts. Though Thales foretold an eclipse of the sun as early as B.C. 600, neither the Greeks nor the Romans had any way of measuring time that was even approximately accurate. Under the republic the normal Roman year contained only three hundred and fifty-five days. Julius Cæsar very nearly corrected the error, although in the time of Pope Gregory XIII., the year had become eleven days too long. It has ceased to be a matter of controversy whether the christian era is four years too short. There is hardly any doubt that the authors of the Homeric Poems had a very undeveloped color-sense. It is highly probable that two or three millenniums ago the countries about the Midland Sea, especially the Ægean, displayed to the appreciative beholder many glorious landscapes which the destruction of the forests and the drying up of the perennial streams have completely obliterated. Not a few streams that formerly flowed all the year round have become temporary torrents, more baneful than beneficent in their effects or beautiful to behold. Many hills that were once covered with natural vegetation now present a parched and barren appearance. In the Homeric Poems we find epithets not a few that felicitously describe natural objects, or at least characterize them, but they are the result of a happy instinct rather than a careful observation. In the long 'Hymn to Demeter,' not many lines are given to an enumeration of the flowers that spring so profusely from the bosom of the earth. The treatment of the subject is perfunctory and superficial. In the much shorter 'Hymn to the Earth, the Mother of All,' flowers are barely mentioned and not particularized. In the brilliant