Template:Selected anniversaries/August 13
1625: Physician, mathematician, and physicist Rasmus Bartholin born. He will discover the double refraction of a light ray by Iceland spar, publishing an accurate description of the phenomenon in 1669.
1819: Physicist and mathematician Sir George Stokes, 1st Baronet born. He will make pioneering contributions to fluid dynamics (including the Navier–Stokes equations) and to physical optics.
1863: Artist Eugène Delacroix dies. His use of expressive brushstrokes and his study of the optical effects of color will shape the work of the Impressionists.
1942: Major General Eugene Reybold of the U.S. Army Corps of Engineers authorizes the construction of facilities that would house the "Development of Substitute Materials" project, better known as the Manhattan Project.