SINCE in an elaborate criticism of Bohr's theory on the constitution of atoms and molecules, Prof. J. W. Nicholson, as in his letter to NATURE (February 5, p 630), comes to the conclusion (Phil. Mag., xxvii., p. 560, 1914) that the valencies of lithium, beryllium, boron, etc., on Bohr's theory are not in accord with experience, and if the electrons in the atoms are to be in one plane, we must either abandon Bohr's method of calculating valency—and (generally) Bohr's theory of the atoms more complex than hydrogen and helium—or give up van den Broek's hypothesis, that the charge of the nucleus of Rutherford's atom is equal to the atomic number (which hypothesis was accepted by Bohr as one of his fundamental assumptions), I may be allowed to add some remarks to my previous letter on this subject (NATURE, March 5, 1914).