[8] See Maxwell, Electricity and Magnetism, vol. i. pp. 284-305 (3rd ed., 1892).
[9] It is an interesting fact that Cavendish measured capacity in “globular inches,” using as his unit the capacity of a metal ball, 1 in. in diameter. Hence multiplication of his values for capacities by 2.54 reduces them to E.S. units in the C.G.S. system. See Elec. Res. p. 347.
[10] For fuller details of these methods of comparison of capacities see J.A. Fleming, A Handbook for the Electrical Laboratory and Testing Room, vol. ii. ch. ii. (London, 1903).
[11] See Fleming, Handbook for the Electrical Laboratory, vol. ii. p. 130.
[12] Faraday, Experimental Researches on Electricity, vol. i. § 1252. For a very complete set of tables of dielectric constants of solids, liquids and gases see A. Winkelmann, Handbuch der Physik, vol. iv. pp. 98-148 (Breslau, 1905); also see Landolt and Börnstein’s Tables of Physical Constants (Berlin, 1894).
[13] See the following papers by J.A. Fleming and James Dewar on dielectric constants at low temperatures: “On the Dielectric Constant of Liquid Oxygen and Liquid Air,” Proc. Roy. Soc., 1897, 60, p. 360; “Note on the Dielectric Constant of Ice and Alcohol at very low Temperatures,” ib., 1897, 61, p. 2; “On the Dielectric Constants of Pure Ice, Glycerine, Nitrobenzol and Ethylene Dibromide at and above the Temperature of Liquid Air,” id. ib. p. 316; “On the Dielectric Constant of Certain Frozen Electrolytes at and above the Temperature of Liquid Air,” id. ib. p. 299—this paper describes the cone condenser and methods used; “Further Observations on the Dielectric Constants of Frozen Electrolytes at and above the Temperature of Liquid Air,” id. ib. p. 381; “The Dielectric Constants of Certain Organic Bodies at and below the Temperature of Liquid Air,” id. ib. p. 358; “On the Dielectric Constants of Metallic Oxides dissolved or suspended in Ice cooled to the Temperature of Liquid Air,” id. ib. p. 368.
[14] See Faraday, Experimental Researches, vol. i. § 1245; R.H.A. Kohlrausch, Pogg. Ann., 1854, 91; see also Maxwell, Electricity and Magnetism, vol. i. § 327, who shows that a composite or stratified dielectric composed of layers of materials of different dielectric constants and resistivities would exhibit the property of residual charge.
[15] Fleming and Ashton, “On a Model which imitates the behaviour of Dielectrics.” Phil. Mag., 1901 [6], 2, p. 228.
[16] The beginner is often puzzled by the constant appearance of the factor 4π in electrical theorems. It arises from the manner in which the unit quantity of electricity is defined. The electric force due to a point-charge q at a distance r is defined to be q/r², and the total flux or induction through the sphere of radius r is therefore 4πq. If, however, the unit point charge were defined to be that which produces a unit of electric flux through a circumscribing spherical surface or the electric force at distance r defined to be ¼πr², many theorems would be enunciated in simpler forms.
[17] See Maxwell, Electricity and Magnetism, vol. i. § 78b (2nd ed.).