“A long time ago Nature made under this tongue of land what man has this day made on its surface.” “What! such a passage exists?” “Yes; a subterranean passage, which I have named the Arabian Tunnel. It takes us beneath Suez and opens into the Gulf of Pelusium.” “But this isthmus is composed of nothing but quicksands?” “To a certain depth. But at fifty-five yards only there is a solid layer of rock.” “Did you discover this passage by chance?” I asked more and more surprised. “Chance and reasoning, sir; and by reasoning even more than by chance. Not only does this passage exist, but I have profited by it several times. Without that I should not have ventured this day into the impassable Red Sea. I noticed that in the Red Sea and in the Mediterranean there existed a certain number of fishes of a kind perfectly identical. Certain of the fact, I asked myself was it possible that there was no communication between the two seas? If there was, the subterranean current must necessarily run from the Red Sea to the Mediterranean, from the sole cause of difference of level. I caught a large number of fishes in the neighbourhood of Suez. I passed a copper ring through their tails, and threw them back into the sea. Some months later, on the coast of Syria, I caught some of my fish ornamented with the ring. Thus the communication between the two was proved.