THAT, as concluded by Prof. Nicholson (NATURE, February 5, p. 630) the atoms of lithium, beryllium, and boron cannot consist of 3, 4, 5 electrons rotating round a nucleus of 3e, 4e, 5e, respectively, with equal angular momenta in one circular orbit, may be concluded also from the periodic system, as instead of 1, 0, 1, 2, 3 electrons of valency, we should then expect a regular increase from 0 to 5, or no valency at all. No atomic model, so far as I know, has succeeded in making this difference plausible; but it is not essential to the hypothesis, that, independently of any atomic model:—(i) Three distinct regions of intra-atomic electrons exist, the number of which (say P, Q, R) may be calculated for each atom from the periodic system; and (ii) on these numbers most, if not all, of the non-periodic properties of the elements depend, so that (NATURE, December 25, 1913, p. 476):—