The Theory of Electrons 567 
order of rising atomic weight, but leaving a gap where necessary to 
bring similar elements into vertical columns, he obtained a periodic 
table with natural vacancies to be filled as new elements were dis- 
covered, and with a certain amount of flexibility at the ends of the 
horizontal lines. From the position of the vacancies, the general 
chemical and physical properties of undiscovered elements could be 
predicted, and the success of such predictions gave a striking proof 
of the usefulness of Mendeléeff’s generalisation. 
When the chemical and physical properties of the elements were 
known to be periodic functions of their atomic weights, the idea of a 
common origin and common substance became much more credible. 
Differences in atomic weight and differences in properties alike might 
reasonably be explained by the differences in the amount of the 
primordial substance present in the various atoms; an atom of 
oxygen being supposed to be composed of sixteen times as much stuff 
as the atom of hydrogen, but to be made of the same ultimate material. 
Speculations about the mode of origin of the elements now began to 
appear, and put on a certain air of reality. Of these speculations 
perhaps the most detailed was that of Crookes, who imagined an 
initial chaos of a primordial medium he named protyle, and a process 
of periodic change in which the chemical elements successively were 
precipitated. 
From another side too, suggestions were put forward by Sir 
Norman Lockyer and others that the differences in spectra observed 
in different classes of stars, and produced by different conditions in 
the laboratory, were to be explained by changes in the structure of 
the vibrating atoms. 
The next step in advance gave a theoretical basis for the idea of 
a common structure of matter, and was taken in an unexpected 
direction. Clerk Maxwell’s electromagnetic theory of light, accepted 
in England, was driven home to continental minds by the confirmatory 
experiments of Hertz, who in 1888 detected and measured the electro- 
magnetic waves that Maxwell had described twenty years earlier. 
But, if light be an electromagnetic phenomenon, the light waves 
radiated by hot bodies must take their origin in the vibrations of 
electric systems. Hence within the atoms must exist electric charges 
capable of vibration. On these lines Lorentz and Larmor have 
developed an electronic theory of matter, which is imagined in its 
essence to be a conglomerate of electric charges, with electro- 
magnetic inertia to explain mechanical inertia’. The movement of 
electric charges would be affected by a magnetic field, and hence the 
1 Larmor, Aether and Matter, Cambridge, 1900. 
