electrons respectively, which are employed to account for the properties of the elements in the earlier periods, the atom also possesses a layer of cells with room for
electrons which is just completed in the case of niton.
In this connection it may be of interest to mention a recent paper by Bury, to which my attention was first drawn after the deliverance of this address, and which contains an interesting survey of the chemical properties of the elements based on similar conceptions of atomic structure as those applied by Lewis and Langmuir. From purely chemical considerations Bury arrives at conclusions which as regards the arrangement and completion of the groups in the main coincide with those of the present theory, the outlines of which were given in my letters to Nature mentioned in the introduction.
Survey of the periodic table. The results given in this address are also illustrated by means of the representation of the periodic system given in [Fig. 1]. In this figure the frames are meant to indicate such elements in which one of the "inner" groups is in a stage of development. Thus there will be found in the fourth and fifth periods a single frame indicating the final completion of the electronic group with
-quanta orbits, and the last stage but one in the development of the group with
-quanta orbits respectively. In the sixth period it has been necessary to introduce two frames, of which the inner one indicates the last stage of the evolution of the group with