Large spinthariscope, 1924.
© Science Museum / Science & Society Picture Library
Made by Adam Hilger Ltd and used by the Nobel prize winner Sir James Chadwick (1891-1974). A spinthariscope is an instrument that measures alpha particles. The neutron was discovered in 1932, after Chadwick had used alpha particles to work out the positive charge of a nucleus and show it to be the same as the atomic number. Chadwick reinterpreted an experiment by the Joliot-Curies and proved the existence of the neutron. This was a masive advance in physics.