discovery of the period-luminosity relation for variable 

 stars (Leavitt, 1912); the determination of the size of the 

 Milky Way (Shapley, 1918); the discovery of the red 

 shift effect of galaxies (Slipher, 1912 — ), and the conclu- 

 sions as to the immense distances of these objects (Hubble, 

 1924); the discovery of radio waves from the Milky Way 

 (Jansky, 1932), and of radio stars (Hey, 1946; Ryle, 

 1952); the continuous origination theory of the universe 

 (Hoyle, 1948); the first astronomical observations from 

 space (of the Sun, 1946). In engineering: the construction 

 of great bridges (George Washington Bridge, 1931; Golden 

 Gate Bridge, 1937); the building of skyscrapers (Rocke- 

 feller Centre Building, 1931 — ); the construction of enor- 

 mous ships (Queen Elizabeth, 1938; United States, 1952); 

 the achievement of powered flight (Wrights, 1903), and 

 the building of huge airliners using the jet engine invented 

 by Whittie (1930); the construction of the Panama Canal 

 (1914); the use of hydroelectric power for the generation 

 of electricity, with the building of great dams (Boulder, 

 1936; Kariba, 1958); the driving of heavy railway trains 

 and large ships with diesel engines, and of large shipys with 

 steam turbo-electric units; the construction of great optical 

 (Palomar, 1951) and radio (Jodrell Bank, 1957; and Cam- 

 bridge, 1958) telescopes; the building of nuclear reactors 

 (c. 1950 onwards) for energy generation and radio-iso- 

 tope production; the construction of immense rockets for 

 journeys into space, and the placing of artificial satellites 

 in circum-terrestrial orbits (1957 — ); the development of 

 long-distance radio communication (Marconi, 1911), and 

 of television (Baird, 1930); the invention of the radio 

 valve (de Forest, 1906) and of the transistor (Bardeen 

 and Brattain, 1948); the construction of electronic com- 

 puters (c. 1950 — ), and of giant "atom-smashers" for 



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