who until 1910 worked at Mason College (later Birmingham University) and then with J. J. Thomson at Cambridge University. In 1919 Aston designed the mass spectrograph (see mass spectroscopy), for which he was awarded the Nobel Prize for chemistry in 1922. With it he discovered the isotopes of neon, and was thus able to explain nonintegral atomic weights. Between 1927 and 1935 he used an improved mass spectrograph to determine atomic weights much more accurately than before. He found that the atomic weights of isotopes are not exactly integer multiples of the atomic weight of hydrogen but are very close to being integers. He explained this by invoking the equivalence between mass and energy found by Albert Einstein in the special theory of relativity, with the ‘missing mass’ being the binding energy of the nucleus.