M. E. Duter, in a paper read before the French Academy in December,
showed that when a Leyden jar is charged with either positive or
negative electricity its internal volume increases, and that this
effect is a new phenomenon, unexplainable by either a theory of an
increase of temperature or of an electrical pressure. The experiment
was performed by means of a flask-shaped Leyden jar with a long tube
attached to its neck, and containing a liquid which served as the
inner armature. The author's attention had been called to the fact
that this phenomenon had been observed ten years ago by M. Gori.
His researches, just made public, leave no doubt of the accuracy of M.
Duter's view, that the glass of the jar really expands. According to
the theory of elasticity, the effect of an internal pressure in a
hollow sphere is in the inverse ratio of its thickness. M. Duter,
therefore, had three flasks made of the same volume, but of
thicknesses of 4 mm., 0.8 mm., and 0.5 mm. respectively. They were
filled with water and enveloped by tin foil. Each carried a capillary
thermometer tube, in which the variations of the height of liquid
served to measure the changes in volume due to electrification. He
found that these changes were imperceptible in the thick glass, very
marked in the flask of mean thickness, and rose to 30 mm. in the
thinnest. The variations in volume were very nearly in inverse ratio
of the square roots of the thicknesses.
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