Page:The fairy tales of science.djvu/364

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modified by experience, but they still remained the types.

Some five-and-twenty years ago, Mr. Scott Russell, then an unknown ship-builder, ventured to question the fitness of these two forms. The fish form would be the best and most perfect, undoubtedly, provided the ship swam under water like a fish, instead of half in and half out; and the duck's-breast bow might prove faultless, if a vessel were merely required to float along the surface like a duck, and not to swim with speed. But he saw that the best constructed ships heaped up a mass of water before them, and that the resistance of this anterior wave could not be overcome without an unprofitable expenditure of power.

Every vessel in passing over the sea displaces a certain amount of water, proportional to its size and draught, and then the water closes in behind her to fill up the hollow. Scott Russell at length discovered the form of ship that would offer the least resistance to the water. He found that the lines or curvature of the bow of a ship ought to resemble the curvature of the wave of displaced water, and that the stern should be curved like the wave of replacement. The mark that still-water makes on the hull of a ship floating on it is called the water-line. Scott Russell called his curve the wave-line, because he found it precisely the same as the line which the wave of displaced water marked along the side of the ship, by which it harmlessly glided without impeding its motion. To test the