The famous experiment which proves that the "earth do move" by letting the observer actually see it twisting underneath his feet, an experiment invented by the French mathematician Jean B. L. Foucault nearly a century ago was repeated recently under unusually impressive circumstances before an international scientific congress at Florence, Italy, the same city where Galileo once was persecuted for holding the same opinion. From the center of the dome of the Church of Santa Maria di Fiore, Father Guido Alfani, director of the Astronomical Observatory, suspended a 200-pound weight on a wire 150 feet long. On the bottom of this weight was a tiny projecting point which traced a line on a table-top sprinkled with sand, as the great pendulum swung slowly back and forth. At a given signal Father Alfani set the pendulum to swinging. While the assembled scientists watched it, slowly the line traced across the sand table-top changed direction. As Foucault proved long ago and as the watching scientists well knew, the table was being twisted underneath the pendulum by the rotation of the earth. A REVOLUTIONARY AIRPLANE A new airplane propeller has recently been patented by J. Kalmanson of Brooklyn, N. Y. Greater speed and marked saving in fuel is claimed for the invention, which may be attached to any type of airplane. The device is in two parts, which may be used separately as front and rear propellers or combined into a single blade. The principle is that the front one acts to bring air to the other, giving the propeller more of a hold, so to speak, and greater power. This is accomplished by four air-spoons, one on each side of each blade of the propeller. It is said that the device can double the speed of an airplane and raise it from the ground in ninety feet instead of the 200 feet most airplanes now require. It is also claimed that the new propeller will prevent the plane from making a nose drive unless the pilot forces it to do so, and enable it to make a safe landing within a short distance. Because of the increase in power and speed, the device would save a large amount of gasoline and oil, as well as guarding the motor from part of the strain on it. The device is said to be also applicable to ships, the same principle operating in water as well as air. Silver Dome _By Harl Vincent_ [Illustration: _Orris led the way to a great underground city._] [Sidenote: In her deep-buried kingdom of Theros, Phaestra reveals the amazing secret of the Silver Dome.]