The Nobel Prize in Chemistry 1922 was awarded to Francis W. Aston "for his discovery, by means of his mass spectrograph, of isotopes, in a large number of non-radioactive elements, and for his enunciation of the whole-number rule".
 

The first attempts in this direction were carried out by the well-known Nobel Prize laureate, Sir J.J.Thomson. In this work he made use of the so-called anode rays, that is to say the positively charged particles of gas which in a vacuum-tube are hurled at a high speed against the negative electrode. Thomson's experiments had not yet led to any decisive result when the outbreak of the World War led to an interruption in the work for several years. Thanks to the substantially increased sharpness and fineness that the analysis of the anode rays has obtained by means of the mass spectrograph, Aston has succeeded in proving that a large number of fundamental elements which have hitherto been regarded as simple are in reality complexes of two or more isotopes.