Tax Day in the U.S.A. 1452: Leonardo Da Vinci was born. 1856: Conrad Hubert, founder of the Ever-Ready Battery Co., was born. 1707: Leonhard Euler, very familiar to all engineering students and renown for his photographic memory, was born. 1912: The British luxury liner RMS Titanic sank in the North Atlantic off Newfoundland less than three hours after striking an iceberg, killing 1,500 people. 1892: The General Electric Company was formed by the merger of the Edison Electric Light Co. and other firms. 1912: The time was spoken of by Einstein as the 4th dimension. 1923: Dr. Lee DeForest demonstrated phonofilm - his technique for putting sound on motion picture film. 1941: Igor Sikorsky made the first helicopter flight over one-hour duration in his VS-300. 1945: British and Canadian troops liberated the Nazi concentration camp Bergen-Belsen. 1952: The first B-52 Bomber prototype was tested in the air. 1964: The Chesapeake Bay Bridge-Tunnel (CBBT) opened, at the time the longest in the world at 17.6 miles shore-to-shore.