The Seven Hills by John Maddox Roberts Page B

direction and another force, or perhaps the same force, in another direction. We feel that there is a principle—"
    "Quite fascinating, I am sure," the queen interrupted. "You must be sure to tell me all about it when you have it all figured out. In the meantime, if you could just show me how wheels benefit a ship?"
    "Of course, Majesty, of course. Well, the outer structure is not precisely a wheel. I have termed it a 'rotary oar.' You see the boards protruding from its perimeter? These are paddles, and they perform the same function as a conventional oar, except that they work in a vertical plane, instead of the horizontal, or, rather the elliptical-horizontal plane of an oar."
    "Chilo," Scipio said, "why not just get it moving? The principle of the thing will be instantly appreciable to Her Majesty then."
    "I suppose so," Chilo said, disappointed.
    "Now he'll sulk," Selene said when the philosopher went off to give his orders to the crew. "There is nothing sadder than a philosopher cheated of a chance to lecture."
    Among the ship's petty officers there was a barking of or ders and a popping of whips, and a piper began to play a rhythmic tune on his double flute. Within the inboard wheels, men began climbing rungs as if ascending a ladder. The outboard wheels started to turn, churning the water. The ship commenced a slow movement. It drew away from the wharf and moved out into the harbor amid a great creak ing of machinery.
    "You see," Chilo explained, "the vertical motion of the slaves climbing is transformed into the rotary motion of the inboard wheel turning. This is in turn transmitted to the outboard wheel, causing the paddles to push against the wa ter, propelling the ship forward. By turning around and climbing the rear of the wheel, the slaves can cause the ship to move backward. Direction can be controlled by causing one wheel to move more slowly than the other, and the steering oar can be used for minor corrections. By working the wheels in opposite directions, the ship can spin quickly on its axis."
    "Very ingenious," the queen allowed. "But oared ships can do all these things, and have for centuries. What is the advantage of these wheels?"
    "There are several," Marcus Scipio informed her. "In the first place, you need far fewer slaves to turn these wheels than to man oars. A ship this size would require at least three hundred, with plenty of relief rowers. Thirty or forty slaves are all you need to man these wheels. They eat far less and that makes for longer voyages."
    "And," said Flaccus, "rowers must be highly skilled. They are expensive and are not replaced easily. Totally, unskilled slaves and convicts can turn these wheels. Nothing is required except for a sound pair of legs."
    "They can't be deaf," Marcus pointed out. "They have to be able to hear the flute."
    Flaccus nodded. "That is true."
    "If a wheel is damaged in battle," Selene pointed out, "it wouldn't be easy to replace, not like a damaged oar."
    "This vessel is a prototype built to test the design," Chilo said. "For a warship, the wheels will have armored cowlings. Only the part that actually touches the water need be exposed." He looked at her expectantly.
    "Very well," she said at last, "you may proceed with this project. What is the next phase?"
    "Trials on the open sea, Your Majesty," Chilo told her. "These can proceed immediately, with this experimental vessel. Upon successful conclusion, a full-sized armed and manned warship will be built and tested. If all goes well, as I am sure it will, a flotilla will be constructed and deployed."
    "The ultimate test will be battle," Scipio said. "If the wheeled ships prove to be more effective in battle, as well as cheaper and less wasteful of manpower, then we will convert entirely to the new system."
    "Your Senate may be displeased to hear of it," she said, smiling. "I hear that they are even now building a fleet on the old model, and taking a great deal of trouble to train rowers."
    "They'll adapt,"