serially in the numerical order of their atomic weights, there is
a curious recurrence of similar properties at intervals of eight
elements This so-called "law of octaves" attracted little
immediate attention, but the facts it connotes soon came under
the observation of other chemists, notably of Professors Gustav
Hinrichs in America, Dmitri Mendeleeff in Russia, and Lothar
Meyer in Germany. Mendeleeff gave the discovery fullest
expression, explicating it in 1869, under the title of "the
periodic law."

Though this early exposition of what has since been admitted to
be a most important discovery was very fully outlined, the
generality of chemists gave it little heed till a decade or so
later, when three new elements, gallium, scandium, and germanium,
were discovered, which, on being analyzed, were quite
unexpectedly found to fit into three gaps which Mendeleeff had
left in his periodic scale. In effect the periodic law had
enabled Mendeleeff to predicate the existence of the new elements
years before they were discovered. Surely a system that leads to
such results is no mere vagary. So very soon the periodic law
took its place as one of the most important generalizations of
chemical science.

This law of periodicity was put forward as an expression of
observed relations independent of hypothesis; but of course the
theoretical bearings of these facts could not be overlooked. As
Professor J. H. Gladstone has said, it forces upon us "the
conviction that the elements are not separate bodies created
without reference to one another, but that they have been
originally fashioned, or have been built up, from one another,