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In the 19th and 20th centuries, [[Russia]] produced many notable [[List of Russian scie At the start of the 18th century the [[Reforms of Peter I of Russia|reforms of Peter the Great]] (founder of ...

...peared throughout history, including the work of [[Desargues]] in the 17th century, all the way back to the implicit use of [[spherical geometry]] to understa ...the theory of [[manifold]]s and [[Riemannian geometry]]. Later in the 19th century, it appeared that geometries without the [[parallel postulate]] ([[non-Eucl ...

...r designed by a commission assembled by Pope Gregory XIII in the sixteenth century."}}{{efn|Many countries that use other calendars for religious purposes use ...ays; when Russia and Greece did so (for their civil calendars) in the 20th century, the jump was 13 days. For other countries and territories, see [[List of a ...

...actions. The system became the standard of France and Europe within half a century. Other measures with unity ratios<ref group="Note">ratios of 1 between mag ...ts for length, mass and time. Advances in [[electromagnetism]] in the 19th century necessitated additional units to be defined, and multiple incompatible syst ...

...the [[seconds pendulum]] (a pendulum with a half-period of one second) one century earlier, but this was rejected as it had been discovered that this length v ...des Archives]]}}, a platinum bar held in Paris. During the mid nineteenth century, following the [[American Revolution]] and [[Decolonization of the Americas ...

...on has noted that Einstein's reminiscences were probably colored by a half-century of hindsight. Norton lists several problems with Einstein's recounting, bot :2. A 19th century [[Aether theories|aether theorist]] would have had no difficulties with the ...