relation of these elements, the affinity of their combinations, their
spectroscopic behaviour, and so forth, make it in the highest degree
probable that they are all merely historical products of an evolutionary
process, having their origin in various dispositions and combinations of
a varying number of original atoms.

To these original or mass-atoms--the ultimate discrete particles of inert
"ponderable matter"--we can with more or less probability ascribe a
number of eternal and inalienable fundamental attributes; they are
probably everywhere in space, of like magnitude and constitution.
Although possessing a definite finite magnitude, they are, by virtue of
their very nature, indivisible. Their shape we may take to be spherical;
they are inert (in the physical sense), unchangeable, inelastic, and
impenetrable by the ether. Apart from the attribute of inertia, the most
important characteristic of these ultimate atoms is their chemical
affinity--their tendency to apply themselves to one another and combine
into small groups in an orderly fashion. These fixed groups (fixed, that
is to say, under the present physical conditions of existence of the
earth) of primitive atoms are the atoms of the elements--the well-known
"indivisible" atoms of chemistry. The qualitative, and, so far as our
present empirical knowledge goes, unchangeable distinctions of our
chemical elements are therefore solely conditioned by the varying number
and disposition of the similar primitive atoms of which they are
composed. Thus, for example, the atom of carbon (the real "maker" of the
organic world) is in all probability a tetrahedron made up of four
primitive atoms.

After Mendelejeff and Lothar Meyer had discovered (1869) the "periodic
law" of the chemical elements, and founded on it a "natural system" of
these elements, this important advance in theoretical chemistry was