The Microcoulomb Experiment

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Abstract
Summary: The present paper deals with the determination of the size and charge of a single submicroscopic particle, measured in a small horizontal condenser of a diameter of approximately 8 mm., using the author's method first stated April 1910. To obtain the highest sensitivity, author used solid particles (spheres) of an order of magnitude under 3 × 10–5 cm. and found charges less than that of the electron. Various objections were raised against his findings, namely that the particles investigated were not spheres, and that their density was not that of the macroscopic substance, so that his findings of charges less than the electronic charge were merely imaginary. The author has succeeded in precipitating and measuring a particle after having observed it in the condenser under normal and also very high gas pressures. The particles were shown to be perfect spheres. A new method is indicated whereby it is possible to determine the size of sub-microscopic spheres by pushing together two equal spheres with a micromanipulator; the two diffraction disks overlap and render it very easy to determine the actual size. It is also possible to show that the density of each individual sphere is that of the macroscopic substance, since it can be computed easily from the velocity of fall at high gas pressures (according to Stokes' law). These two data being accurately determined, the author still found charges considerably less than the electronic charge, and the deviations are too great to be accounted for by errors of observation. The reason that the author has used a solid substance (red amorphous Se) and not oil, which is a liquid, was in the first place, that liquids evaporate, and therefore do not yield correct results, and secondly, because liquid spheres are not certain to preserve their sphericity when precipitated. Thus charges less than that of the electron are to be considered as actually existing.