In 1986, we marked the 50th anniversary of the discovery of the earth's innercore. In atomic physics an equivalent act would warrant a Nobel prize. The credit is due to Inge Lehmann (Figure 1), who in 1936 was working as a seismologist at the Royal Danish Geodetic Institute, Copenhagen. Her proposal was published in the Bureau Central Seismologique International, Travaux Scientifique [Lehmann, 1936]:An explanation of the P3′ wave [i.e., PKIKP] is required, since now it can hardly be considered probable that it is due to diffraction. A hypothesis will be here suggested which seems to hold some probability, although it cannot be proved from the data at hand. We take it… that inside the core there is an inner core in which the velocity is larger than the outer core.