Hydrogen, electro-chemical equivalent of, 267. I. Ice-pail experiment of Faraday, 270. Identity of frictional and voltaic electricity, 266. Induced currents, discovered by Faraday, 259; explained by structure of ether, 304; from earth's action, 262. Induction coil, 320. Induction, Franklin's experiments on, 90; self, 142, 306. Induction machines, principle of, 316. Insulators for lightning-rods, 96. Interference, principle of, discovered by Young, 208; spectra of, obtained by Young, 225. Invisible college, 13. J. Jenkin, William, discovery of the "extra current" by, 268. Joule and Thomson's determination of the heat absorbed by air in expanding, 324. Joule, Dr., establishment of mechanical theory of heat by, 193, 324. Joule's law, 324; proof that heat and energy are equivalent, 324; determination of the mechanical equivalent of heat, 325. Junto Club, formation of the, 51. K. Kelland's, Professor, edition of Young's lectures, 212. Kinnersley commences lecturing, 73. Kite, Franklin's, 88. Knobs _versus_ points, 95. L. Laboulaye's comments on Franklin, 38. Laplace's theory of Saturn's rings, 285. Latent heat, Black's theory of, 144; Cavendish's views on, 144. Leonardo da Vinci's observation of capillary attraction, 228. Leyden jar, discovery of, 4; energy of, resident in the glass, 79. Leyden jars charged by cascade, 77. Light, Franklin's view of nature of, 86; Maxwell's electro-magnetic theory of, 306; rotation of the plane of polarization of, 273. Lightning, effects of, on Newbury steeple, 92. Lightning-protectors, Maxwell's, 294. Lightning-rod, illustrations of the, 83. _Lignum nephriticum_, dichroism of, 30. Lines of force mathematically investigated by Thomson and Maxwell, 300. Lines of magnetic force fixed by Faraday, 269. Luminiferous ether, the vehicle of electrical action, 227; illustration of the possible constitution of, 302. M. Magdeburg hemispheres, experiments with, by Otto von Guericke, 17. Magic squares, Franklin's proficiency in, 66. "Magnetic spark" obtained by Faraday, 262. Magnetization by induction, Boyle's experiments on, 34. Magneto-electric machine, Faraday's, 262, 314. Magneto-electric machines, Wilde's, 318; objects to be aimed at in the construction of, 315.