The year 1919 in science and technology involved some significant events, listed below.
Astronomy
April – George Ellery Hale and collaborators publish their discovery that the magnetic polarity of sunspot pairs reverses on an 11-year solar cycle and that the polarity varies by hemisphere, which becomes known as Hale's law.[1][2]
James Jeans discovers that the dynamical constants of motion determine the distribution function for a system of particles.
Betz's law is published by German physicist Albert Betz, indicating the maximum power that can be extracted from the wind, independent of the design of a wind turbine in open flow.
^Verhandlungen der Deutschen Physikalischen Gesellschaft.; Mehra, Jagdish; Rechenberg, Helmut (1982). The Historical Development of Quantum Theory. Vol. 1, Part 1: The Quantum Theory of Planck, Einstein, Bohr and Sommerfeld 1900–1925: its Foundation and the Rise of Its Difficulties. Springer. p. 330. ISBN978-0-387-95174-4.