There is a large accumulation of evidence in support of Sir Ernest Rutherford's conception of atomic structure. According to this conception an uncharged atom consists of certain groupings of negative electrons rotating about a positively charged nucleus. Dr Bohr's theory of line spectra, which is based on this structure, frankly discards dynamical conditions of stability. There is no doubt, however, that this theory has been very successful in accounting for the numerical relationships between the frequencies of spectral lines.