英語時差：為什么一天有24小時？（下）

If you drop the ball, gravity will pull it toward the center of the earth, but will not diminish that extra eastward speed. So as the ball falls it’ll outrun the ground and land slightly east of the straight-down point. Edwin H. Hall, a Harvard University physicist, looked for this effect in 1902. Working in an enclosed tower, he dropped one-inch bronze balls from a height of 75 feet into a pan of tallow. Hall was careful. He built a mechanism to release the ball without jiggle or spin, and a cloth tube to protect the path of fall from breezes. He used high-precision surveying telescopes to measure the position of a plumb line before each drop, and the position of the ball afterward. He made a total of 948 drops. The average eastward deflection was just as predicted by Newton’s laws for a 75-foot tower at the latitude of Cambridge, Massachusetts: about one-seventeenth of an inch.