Template:Are You Sure/April 18
• ... that the 1906 San Francisco earthquake struck the coast of Northern California at 5:12 a.m. on April 18 with an estimated moment magnitude of 7.9; that devastating fires soon broke out in the city and lasted for several days; and that as a result, up to 3,000 people died and over 80% of the city of San Francisco was destroyed?
• ... that mathematician Karl Mikhailovich Peterson gave, in his graduation dissertation (1853, but not published until later), an early formulation of the fundamental equations of the surface theory, now usually known as Gauss–Codazzi equations, sometimes Peterson–Codazzi equations?
• ... that philosopher, logician, mathematician, and scientist Charles Sanders Peirce saw, as early as 1886, that logical operations could be carried out by electrical switching circuits, anticipating logic gates?