As this route for trade became known, the geographers began to understand the wide space that separates India from Africa. Hitherto, notwithstanding a few voyages of discovery, it had been the common opinion that Persia was in the neighbourhood of Ethiopia. The Greeks had thought that the Nile rose in India, in opposition to the Jews, who said that it was the river Gibon of the garden of Eden, which made a circuit round the whole of the land of Cush, or Ethiopia. The names of these countries got misused accordingly; and even after the mistake was cleared up we sometimes find Ethiopia called India. The Egyptian chemists were able to produce very bright dyes by methods then unknown to Greece or Rome. They dipped the cloth first into a liquid of one colour, called a mordant, to prepare it, and then into a liquid of a second colour; and it came out dyed of a third colour, unlike either of the former. The ink with which they wrote the name of a deceased person on the mummy-cloth, like our own marking-ink, was made with nitrate of silver. Their knowledge of chemistry was far greater than that of their neighbours, and the science is even now named from the country of its birth. The later Arabs called it Alchemia, _the Egyptian art_, and hence our words alchemy and chemistry. So also Naphtha, or _rock oil_, from the coast of the Red Sea; and Anthracite, or _rock fuel_, from the coast of Syria, both bear Egyptian names. To some Egyptian stones the Romans gave their own names; as the black glassy obsidian from Nubia they called after Obsidius, who found it; the black Tiberian marble with white spots, and the Augustan marble with regular wavy veins, were both named after the emperors. Porphyry was now used for statues for the first time, and sometimes to make a kind of patchwork figure, in which the clothed parts were of the coloured stone, while the head, hands, and feet were of white marble. And it was thought that diamonds were nowhere to be found but in the Ethiopian gold mines.