In recent years various suggestions have been made as to the nature of the change which constitutes electric displacement. One theory, due to Von Helmholtz, supposes that the electro-kinetic momentum, or vector potential of Maxwell, is actually the momentum of the moving ether; according to another, suggested, it would appear originally in a crude form by Challis, and developed within the last few months in very satisfactory detail by Larmor, the velocity of the ether is magnetic force; others have been devised, but we are still waiting for a second Newton to give us a theory of the ether which shall include the facts of electricity and magnetism, luminous radiation, and it may be gravitation.[71] Meanwhile we believe that Maxwell has taken the first steps towards this discovery, and has pointed out the lines along which the future discoverer must direct his search, and hence we claim for him a foremost place among the leaders of this century of science. FOOTNOTES [1] A full biographical account of the Clerk and Maxwell families is given in a note by Miss Isabella Clerk in the “Life of James Clerk Maxwell,” and from this the above brief statement has been taken. [2] “Life of J. C. Maxwell,” p. 26. [3] “Life of J. C. Maxwell,” p. 27. [4] “Life of J. C. Maxwell,” p. 49. [5] “Life of J. C. Maxwell,” p. 52. [6] “Life of J. C. Maxwell,” p. 56. [7] “Life of J. C. Maxwell,” p. 67. [8] “Life of J. C. Maxwell,” p. 75. [9] Professor Garnett in _Nature_, November 13th, 1879. [10] “Life of J. C. Maxwell,” p. 105. [11] “Life of J. C. Maxwell,” p. 116. [12] “Life of J. C. Maxwell,” pp. 123–129. [13] “Life of J. C. Maxwell,” p. 190. [14] Dean of Canterbury. [15] Master of Trinity. [16] “Life of J. C. Maxwell,” p. 174. [17] “Life of J. C. Maxwell,” p. 195. [18] “Life of J. C. Maxwell,” p. 207. [19] “Life of J. C. Maxwell,” p. 208. [20] “Life of J. C. Maxwell,” p. 210. [21] “Life of J. C. Maxwell,” p. 211. [22] “Life of J. C. Maxwell,” p. 216. [23] “Life of J. C. Maxwell,” p. 256. [24] “Life of J. C. Maxwell,” p. 267. [25] “Life of J. C. Maxwell,” p. 269. [26] “Life of J. C. Maxwell,” p. 278. [27] “Life of J. C. Maxwell,” p. 292. [28] “Life of J. C. Maxwell,” p. 303. [29] “Life of J. C. Maxwell,” p. 259. [30] B.A. Report, Newcastle, 1863. [31] “Life of J. C. Maxwell,” p. 340. [32] “Life of J. C. Maxwell,” p. 332. [33] “Life of J. C. Maxwell,” p. 336. [34] The Professors who were consulted were Challis, Willis, Stokes, Cayley, Adams, and Liveing. [35] “Life of J. C. Maxwell,” p. 349. [36] “Life of J. C. Maxwell,” p. 381. [37] “Life of J. C. Maxwell,” p. 379. [38] An account of the laboratory is given in _Nature_, vol. x., p. 139.