IN a previous paper(On the constitution of atoms and molecules) the writer has shown that an explanation of some of the laws of line spectra may be obtained by applying Planck’s theory of black radiation to Rutherford’s theory of the structure of atoms. In the present paper these considerations will be further developed, and it will be shown that it seems possible on the theory to account for some of the characteristic features of the recent discovery by Stark[ of the effect of an electric field on spectral lines, as well as of the effect of a magnetic field first discovered by Zeeman. It will also be shown that the theory seems to offer an explanation of the appearance of ordinary double spectral lines