Just then Rollo heard a rapping sound upon the stone of the sidewalk near him. He looked round to see what it was. There was a blind man coming along. He had a stick in his hand, which seemed to be armed at the lower end with a little ferule of iron. With this iron the blind man kept up a continual rapping on the flagstones as he slowly advanced. The iron produced a sharp and ringing sound, which easily made itself heard above the thundering din of the carriages and vans that were rolling incessantly over the bridge, and served as a warning to the foot passengers on the sidewalk that a blind man was coming. Every one hearing this rapping looked up to see what it meant; and, perceiving that it was a blind man, they moved to one side and the other to make way for him. Thus, though the sidewalk was so crowded that a person with eyes could scarcely get along, the blind man, though he moved very slowly, had always vacant space before him, and advanced without any difficulty or danger.[B] [B] See frontispiece. "Think of a blind man in such a crowd as this!" said Rollo. "Yes," said Mr. George. "And he gets along better than any of the rest of us," said Rollo. "Yes," said Mr. George, "so it seems." "The next time I wish to go through a crowd," said Rollo, "I mean to get a cane, and then shut my eyes and rap with it, and every body will make room for me." "Look round here a minute more," said Mr. George; "there is something else that I wish to explain to you. You see there are no bridges below this, though there are a great many above." "Yes," said Rollo; "and how do they get across the river below here? Are there ferry boats?" "I think it likely there are ferry boats down below," said Mr. George. "At any rate, there are plenty of small boats which any body can hire. They are rowed by men called watermen. "'Bound 'prentice to a waterman, I learned a bit to row.'" "What poetry is that?" said Rollo. "It is part of some old song," said Mr. George. "Look down the river and you can see these boats cruising about among the shipping." "Is that the way they get across the river below here?" said Rollo. "Yes," said Mr. George; "and then there is the Tunnel besides. They can go _under_ the river through the Tunnel if they please, about a mile and a half below here." "Is that the reason why they made the Tunnel," said Rollo, "because they could not have any bridge?" "Yes," said Mr. George. "It would have been a great deal cheaper and better to have made a bridge; but a bridge would have interfered with the shipping, and so they made a tunnel underneath." "I never knew before," said Rollo, "why they made the Tunnel." "Yes," said Mr. George, "that is the reason. It was a very difficult and expensive work; but I believe it proved a failure. Very few people use it for crossing the river, though a great many go to see it. It is a curious place to see. But now let us go across the bridge and see what is on the other side."