Great bridges present some of the most remarkable triumphs of the engineer. They rank beside the express locomotive and the ocean liner as among the great constructive achievements of mankind. Daring in design, and bold in execution and in sweep of span, they have been developed along several principles; and so solidly have they been built, so sound are the laws of their being, that it seems as though they will live as long as the everlasting hills.
REMARKABLE TUNNELS AND THEIR CONSTRUCTION.
CHAPTER I.
HOW BRUNEL MADE A BORING-SHIELD.
“I watched the worm at work and took my idea from that tiny creature!”
“A worm! Was it an ordinary worm?”
“Oh no, it was the naval wood-worm—Teredo Navalis; it can bore its way through the hardest timber. I was in a dockyard and I saw the movements of this animal as it cut its way through the wood, and the idea struck me that I could produce some machine of the kind for successful tunnelling.”