When the dominion of the Romans supervened upon that of the Greeks, and bore all irresistibly to the West, much that was glorious appeared to be obscured, but nothing was lost. All the materials which flowed into the vast stream of Roman civilization, from the valley of the Nile, from Phœnicia, the Euphrates, and the Ilissus, arrived by ways and in times which infinite wisdom saw to be best, and from Octavius to Constantine were amalgamated, and thenceforth still further removed for the grandest use. From India to the Atlantic coast, from Libyan borders to Caledonian hills, not only was the greatest variety in the forms of earth, its organic productions and physical phenomena presented to general notice, but also the human race was seen in all the gradations of civilized and savage life. In the East, effete races existed still in the possession of ancient knowledge, and in the exercise of ancient arts; while in the West, over gathering hordes of energetic barbarians, the fresh dawn of a mightier life was beginning to rise. In the time of Ælius Gallius and Bulbus, distant scientific expeditions were undertaken; and under Augustus, a general survey of the entire empire was commenced by Zenodoxus and Polycletus. The same Grecian geometricians, or others under their direction, prepared itineraries and special topographical accounts to be distributed among the rulers of the several provinces. They were the first statistical works undertaken in Europe. Roads were divided into miles, and extended to the remotest boundaries, so that Hadrian, in an uninterrupted journey which occupied eleven years, traveled with ease from the peninsula of Iberia to Judea, Egypt, and Mauritania. It might reasonably be expected that such a vast field, so diversified in climate and productions, and which might with so much facility be explored by state officers and their retinues of learned men, would have produced numerous proficients in science. On the contrary, during the four centuries, when the Romans held undivided sway over the known world, Dioscorides the Cilician, and Galenus of Pergamus, were the only natural philosophers. The first made some approach to botanical science, and increased the number of species of plants, which had been described. And it was at this time that Galen, by the care of his dissections, and the extent of physiological researches, has been declared worthy of being placed near to Aristotle, and generally above him. Ptolemæus, whom we before mentioned as a systematic astronomer and geographer, is a third bright name to be added to the experimental philosophers Dioscorides and Galen. He measured the refraction of light, and was the first founder of an important part of optics. All these distinguished masters of such science as existed among the Romans were Greeks, as we have before seen was the case with the prime leaders in the departments of literature and art.