POINCARE, Henri. "Sur le dynamique de l'electron", in Comptes Rendus, Paris,  1905, volume 140, pp 1504-1508, offered in the entire bound volume of 1749pp for the half year.  Bound in boards and  leather spine, the spine cover nearly detached.  A good copy.  $550  (English translation found here.)

"HENRI POINCARE'S major work on a theory of the electron is "Sur la dynamique de l'electron".  It is considered, by some, as evidence that POINCARE, more than anyone else in the late 19th and early 20th centuries, anticipated EINSTEIN'S 1905 theory of relativity."

"This study will focus on POINCARE'S attempt in "Sur la dynamique..." to formulate a purely electromagnetic theory of a deformable electron that is consonant with his conception of the principle of relativity. PPoincare believed that if all physical processes could be reduced ultimately to the interaction of charged particles which move about in LORENTZ'S all-pervasive ether, then such a theory would be an important step toward a unified description of nature. Thus,  the laws of the various branches of physics, and in particular NEWTON'S second law,  could be derived from those of electromagnetism. This scientific viewpoint (or  Weltbild) will hereafter be referred to as the "electromagnetic world-picture. ''...--From the introduction of Arthur Miller's fine study of this paper in Archive for History of Exact Sciences, Vol. 10, No. 3/4/5 (18.IX.1973), pp. 207-328, "A Study of Henri Poincaré's "Sur la Dynamique de l'Électron"."

It has always seemed strange to me that Poincare never followed up on this paper, nor did he seem publicly (?) interested in Einstein's great work of 1905; nor did Einstein show much interest in Poincare's work on this topic (or nearly any other), and was otherwise indisposed when he was approached to write an appreciation of Poincare upon is death six years later.