When these elementary books have been digested, the advanced student may proceed to study the following: J. Clerk Maxwell, _A Treatise on Electricity and Magnetism_ (1st ed., Oxford, 1873; 2nd ed. by W.D. Niven, 1881; 3rd ed. by J.J. Thomson, 1892); Joubert and Mascart, _Electricity and Magnetism_, English translation by E. Atkinson (London, 1883); Watson and Burbury, _The Mathematical Theory of Electricity and Magnetism_ (Oxford, 1885); A. Gray, _A Treatise on Magnetism and Electricity_ (London, 1898). In the collected _Scientific Papers_ of Lord Kelvin (3 vols., Cambridge, 1882), of James Clerk Maxwell (2 vols., Cambridge, 1890), and of Lord Rayleigh (4 vols., Cambridge, 1903), the advanced student will find the means for studying the historical development of electrical knowledge as it has been evolved from the minds of some of the master workers of the 19th century. (J. A. F.) FOOTNOTES: [1] See Maxwell, _Elementary Treatise on Electricity_ (Oxford, 1881), p. 47. [2] See Maxwell, _Treatise on Electricity and Magnetism_ (3rd ed., Oxford, 1892), vol. i. p. 80. [3] Maxwell, Ibid. vol. i. § 74a; also _Electrical Researches of the Hon. Henry Cavendish_, edited by J. Clerk Maxwell (Cambridge, 1879), p. 104. [4] Laplace (_Mec. Cel._ vol. i. ch. ii.) gave the first direct demonstration that no function of the distance except the inverse square can satisfy the condition that a uniform spherical shell exerts no force on a particle within it. [5] The solution of the problem of determining the distribution on an ellipsoid of a fluid the particles of which repel each other with a force inversely as the nth power of the distance was first given by George Green (see Ferrer's edition of Green's _Collected Papers_, p. 119, 1871). [6] See Thomson and Tait, _Treatise on Natural Philosophy_, § 519. [7] See article "Electricity," _Encyclopaedia Britannica_ (9th edition), vol. viii. p. 30. The reader is also referred to an article by Lord Kelvin (_Reprint of Papers on Electrostatics and Magnetism_, p. 178), entitled "Determination of the Distribution of Electricity on a Circular Segment of a Plane, or Spherical Conducting Surface under any given Influence," where another equivalent expression is given for the capacity of an ellipsoid. [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).