The gold mines near the Nubian or Golden Berenice, though not so rich as they used to be, were worked with full activity by the unhappy prisoners, criminals, and slaves, who were there condemned to labour in gangs under the lash of their taskmasters. Men and women alike, even old men and children, each at such work as his overstretched strength was equal to, were imprisoned in these caverns tunnelled under the sea or into the side of the mountain; and there by torchlight they suffered the cruel tortures of their overseers without having power to make their groans heard above ground. No lot upon earth could be more wretched than that of these unhappy men; to all of them death would have been thought a boon. The survey of the coast of the Red Sea, which was undertaken in this or the last reign, did not reach beyond the northern half of that sea. It was made by Agatharcides, who, when the philosopher Heracleides Lembus filled the office of secretary to the government under Philometor, had been his scribe and reader. Agatharcides gives a curious account of the half-savage people on these coasts, and of the more remarkable animals and products of the country. He was a most judicious historian, and gave a better guess than many at the true cause of why there was most water in the Nile in the dry est season of the year; which was a subject of never-ceasing inquiry with the travellers and writers on physics. Thaies said that its waters were held back at its mouths by the Etesian winds, which blow from the north during the summer months; and Democritus of Abdera said that these winds carried heavy rain-clouds to Ethiopia; whereas the north winds do not begin to blow till the Nile has risen, and the river has returned to its usual size before the winds cease. Anaxagoras, who was followed by Euripides, the poet, thought that the large supply of water came from the melting of snow in Ethiopia. Ephorus thought that there were deep springs in the river's bed, which gushed forth with greater force in summer than in winter. Herodotus and OEnopides both thought that the river was in its natural state when the country was overflowed; and the former said that its waters were lessened in winter by the attraction of the sun, then over Southern Ethiopia; and the latter said that, as the earth grew cool, the waters were sucked into its pores. The sources of the Nile were hidden by the barbarism of the tribes on its banks; but by this time travellers had reached the region of tropical rains; and Agatharcides said that the overflow in Egypt arose from the rains in Upper Ethiopia. But the Abyssinian rains begin to fall at midsummer, too late to cause the inundation in Egypt; and therefore the truth seemed after all to lie with the priests of Memphis, who said the Nile rises on the other side of the equator, and the rain falling in what was winter on that side of the globe made the Nile overflow in the Egyptian summer.