Zamenhof Day Zamenhof Day Zamenhof Day (), also called Esperanto Book Day, is celebrated on 15 December, the birthday of Esperanto creator L. L. Zamenhof. It is the most widely celebrated day in Esperanto culture. On this day, Esperantists hold information sessions and cultural gatherings to promote literature in Esperanto. The history of celebrating Esperanto on Zamenhof's birthday can be traced back to 17 December 1878, when at a birthday party for his 19th birthday he presented to his friends his "Lingwe uniwersala", the first version of his international language. By 1887, this language had evolved into what is now recognized as
Ludwik Silberstein structures ("struts", "ropes", or "membranes") that are responsible for holding masses against the attractive force of gravity in a static configuration. According to Martin Claussen, Ludwik Silberstein initiated a line of thought involving eddy currents in the atmosphere, or fluids generally. He says that Silberstein anticipated foundational work by Vilhelm Bjerknes (1862 – 1951). Ludwik Silberstein Ludwik Silberstein (1872 – 1948) was a Polish-American physicist who helped make special relativity and general relativity staples of university coursework. His textbook "The Theory of Relativity" was published by Macmillan in 1914 with a second edition, expanded to include general relativity, in 1924.