Mass spectrometer

Aston improved on Thomson's apparatus so that it was capable of delicately separating ions by their mass for photographic detection. It showed that elements could have multiple stable isotopes, each with the same charge but differing mass numbers, for example Chlorine 35 and 37.
 Francis William Aston England 1919 Mass spectrometer

Aston improved on Thomson's apparatus so that it was capable of delicately separating ions by their mass for photographic detection. It showed that elements could have multiple stable isotopes, each with the same charge but differing mass numbers, for example Chlorine 35 and 37.