The American physicist and Nobel Prize winner Ernest Orlando Lawrence invented the cyclotron, an instrument used to study the structure of matter. Particles set in motion in an acceleration chamber collide with a "target" — the body under investigation. Frédéric Joliot-Curie used this cyclotron, which the Collège de France acquired in 1937, to study nuclear transmutation (the transformation of bodies during a nuclear reaction). It had a 25-ton electromagnet. Modified and installed at the Orsay Nuclear Physics Laboratory in 1958, it has been at the Musée des arts et métiers since 1969. The cyclotron attests to the development of scientific research in the 20th century, marked by the emergence of Big Science that cleared the way for increasingly imposing instruments, like the CERN's Large Hadron Collider.