Rabi is an American who worked for some time with Stern in Hamburg and is now professor at Columbia University, New York. He developed the same ray method to a considerable precision for the measurement of the magnetic properties of atomic nuclei. His apparatus is based on the fact that one can produce ordinary electromagnetic oscillations of the same frequency as that of the Larmor precession of atomic systems in a magnetic field. By an ingenious application of the resonance principle he succeeded in detecting and measuring single states of rotation of atoms and molecules, and in determining the mechanical and magnetic moments of the nuclei. A Nobel Prize has been awarded to him for his great contribution to our knowledge of nuclear magnetism.