Davy, Sir Humphry, appointed professor at the Royal Institution, 174; letter of, to Faraday, 244. Declaration of American Independence signed, 113. Defence of the American Colonies against France and Spain, 62. Degree of electrification, 137. De la Rive's invitation to Faraday, 249. Density of the earth, determinations of the mean, 146. Desaguliers on electrics and non-electrics, 4. Diagram of colour, Young's, 215; Maxwell's, 295. Diamagnetism discovered by Faraday, 274. Diamonds burned by Davy, 250. Dichroism of _Lignum nephriticum_, 30. Discharge, electrical, difference between positive and negative, 87. Dissipation of energy, principle of, 326. Distilled water, resistance of, 142. Double refraction explained by Huyghens, 219. Dufay showed that all bodies could be electrified, 4. Dynamical nature of heat, suggested by Bacon, 2, 32; maintained by Boyle, 32; investigated by Rumford, 189; established by Joule, 193, 324. Dynamical top, Maxwell's, 285. Dynamo, constructed by Wheatstone, 318; action of, 319; essential feature of, 319. E. Effect of points in discharging electricity, 74. Electrical picnic, 80. Electrical Standards Committee, 287. Electric intensity, 137; potential, 137. Electricity, first obtained from clouds, 74; velocity of, 93. Electrics and non-electrics, 3. Electrolysis, Faraday's laws of, 266. Electro-magnetic induction, discovered by Faraday, 259; Maxwell's statement of the laws of, 301. Electro-magnetic theory of light, 306. Electro-motors, 313. Electro-tonic state, conceived by Faraday, 264; explained by Maxwell, 302. Energy of Leyden jar resident in the glass, 79. Eriometer, Young's, 223. Ether, Maxwell's illustration of the possible constitution of, 302. Expansion of water on freezing, 33. Extra current, 268. F.