  A complete history of early atomic models would fill volumes, but a
reasonably coherent tale of the path from mechanical atoms to the quantum can
be told by focusing on the relevant work of three great contributors to atomic
physics, in the critically important years between 1904 and 1913: J. J.
Thomson, Ernest Rutherford and Niels Bohr. We first examine the origins of
Thomson's mechanical atomic models, from his ethereal vortex atoms in the early
1880's, to the myriad "corpuscular" atoms he proposed following the discovery
of the electron in 1897. Beyond predictions for the periodicity of the
elements, the application of Thomson's atoms to problems in scattering and
absorption led to quantitative predictions that were confirmed by experiments
with high-velocity electrons traversing thin sheets of metal. Still, the much
more massive and energetic {\alpha}-particles being studied by Rutherford were
better suited for exploring the interior of the atom, and careful measurements
on the angular dependence of their scattering eventually allowed him to infer
the existence of an atomic nucleus. Niels Bohr was particularly troubled by the
radiative instability inherent to any mechanical atom, and succeeded in 1913
where others had failed in the prediction of emission spectra, by making two
bold hypotheses that were in contradiction to the laws of classical physics,
but necessary in order to account for experimental facts.
