Template:On This Day (nonfiction)/April 15
1452: Polymath Leonardo da Vinci born. His areas of interest will include painting, sculpting, architecture, invention, science, music, mathematics, engineering, literature, anatomy, geology, astronomy, botany, writing, history, and cartography.
1552: Mathematician and astronomer Pietro Cataldi born. Cataldi will contribute to the development of continued fractions and a method for their representation; he will also discover the sixth and seventh perfect numbers by 1588.
1707: Mathematician and physicist Leonhard Euler born. He will make important and influential discoveries in many branches of mathematics, and will introduce much of the modern mathematical terminology and notation, such as the notion of a mathematical function.
1764: Astronomer and mathematician Peder Horrebow dies. he invent a way to determine a place's latitude from the stars.
1878: Physicist Ernst Ruhmer born. Ruhmer will invent applications for the light-sensitivity properties of selenium, including wireless telephony using line-of-sight optical transmissions, sound-on-film audio recording, and television transmissions over wires.
1911: Physicist Johannes Bosscha Jr. dies. Bosscha made important investigations on galvanic polarization and the rapidity of sound waves; he was one of the first (1855) to suggest the possibility of sending two messages simultaneously over the same wire.
1926: Aviator Charles Lindbergh opens service on the newly designated 278-mile (447 km) Contract Air Mail Route #2 (CAM-2) to provide service between St. Louis and Chicago (Maywood Field) with two intermediate stops in Springfield and Peoria, Illinois.
1983: Mathematician Vera Faddeeva dies. Faddeeva pioneered the field of linear algebra; her Computational Methods of Linear Algebra (1950) was widely acclaimed.
2014: Engineer and academic John Houbolt dies. Houbolt promoted the lunar orbit rendezvous (LOR) mission mode for space travel, a concept that was used to successfully land humans on the Moon and return them to Earth.