  This paper is centered on some historical aspects of nuclear masses, and
their relations to major discoveries. Besides nuclear reactions and decays, the
heart of mass measurements lies in mass spectrometry, the early history of
which will be reviewed first. I shall then give a short history of the mass
unit which has not always been defined as one twelfth of the carbon-12 mass.
When combining inertial masses from mass spectrometry with energy differences
obtained in reactions and decays, the conversion factor between the two is
essential. The history of the evaluation of the nuclear masses (actually atomic
masses) is only slightly younger than that of the mass measurements themselves.
In their modern form, mass evaluations can be traced back to 1955. Prior to
1955, several tables were established, the oldest one in 1935.
