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Encyclopaedia Britannica, 11th Edition, "Electrostatics" to "Engis": Volume 9, Slice 3Various

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Encyclopaedia Britannica, 11th Edition, "Electrostatics" to "Engis": Volume 9, Slice 3

Name: Encyclopaedia Britannica, 11th Edition, "Electrostatics" to "Engis": Volume 9, Slice 3
Author: Various

Various

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_Dielectric constant._--Since all electric charge consists in a state of
strain or polarization of the dielectric, it is evident that the
physical state and chemical composition of the insulator must be of
great importance in determining electrical phenomena. Cavendish and
subsequently Faraday discovered this fact, and the latter gave the name
"specific inductive capacity," or "dielectric constant," to that quality
of an insulator which determines the charge taken by a conductor
embedded in it when charged to a given potential. The simplest method of
determining it numerically is, therefore, that adopted by Faraday.[12]
He constructed two equal condensers, each consisting of a metal ball
enclosed in a hollow metal sphere, and he provided also certain
hemispherical shells of shellac, sulphur, glass, resin, &c., which he
could so place in one condenser between the ball and enclosing sphere
that it formed a condenser with solid dielectric. He then determined the
ratio of the capacities of the two condensers, one with air and the
other with the solid dielectric. This gave the dielectric constant K of
the material. Taking the dielectric constant of air as unity he obtained
the following values, for shellac K = 2.0, glass K = 1.76, and sulphur K
= 2.24.

  TABLE I.--_Dielectric Constants (K) of Solids (K for Air = 1)._

  +----------------------------------+-------+--------------------+
  |            Substance.            |   K.  |     Authority.     |
  +----------------------------------+-------+--------------------+
  | Glass, double extra dense flint, |       |                    |
  |   density 4.5                    | 9.896 | J. Hopkinson       |
  | Glass, light flint, density 3.2  | 6.72  |      "             |
  | Glass, hard crown, density 2.485 | 6.61  |      "             |
  |                                / | 2.24  | M. Faraday         |
  |                                | | 2.88  | Coullner           |
  | Sulphur  . . . . . . . . . . .<  | 3.84  | L. Boltzmann       |
  |                                | | 4.0   | P.J. Curie         |
  |                                \ | 2.94  | P.R. Blondlot      |
  |                                / | 2.05  | Rosetti            |
  |                                | | 3.15  | Boltzmann          |
  | Ebonite  . . . . . . . . . . .<  | 2.21  | Schiller           |
  |                                \ | 2.86  | Elsas              |
  | India-rubber, pure brown         | 2.12  | Schiller           |
  | India-rubber, vulcanized, grey   | 2.69  |     "              |
  | Gutta-percha                     | 2.462 | J.E. H. Gordon     |
  |                                / | 1.977 | Gibson and Barclay |
  |                                | | 2.32  | Boltzmann          |
  | Paraffin . . . . . . . . . . .<  | 2.29  | J. Hopkinson       |
  |                                \ | 1.99  | Gordon             |
  |                                / | 2.95  | Wällner            |
  | Shellac  . . . . . . . .

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Encyclopaedia Britannica, 11th Edition, "Electrostatics" to "Engis": Volume 9, Slice 3

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