Magnets, cast iron, xxxiii, 265. ----, chemical action in needles suspended from, xviii, 402. ----, best position of, for mutual action, _H. Lloyd_, xxxviii, 96. ----, current produced by the rotation of, _Pixii_, xxiv, 144, 146.^f ----, electric spark from, _J. Henry_, xxii, 403. ----, a mode of producing sparks and galvanic currents from the horse shoe, _J. P. Emmet_, xxiv, 78.^f ----, new method of making permanent, xxxvi, 335.^f ----, galvanic, construction of, _J. B. Zabriskie_, xxxvi, 124.^f ----, ----, Henry's large, xix, 408.^f ----, ----, made for Laboratory of Yale College, xx, 201. ----, ----, Humbert's, xxxviii, 204. ----, ----, Ganby's, xxix, 354. ----, ----, Page's, xxxv, 253.^f ----, ----, E. M. Clarke's, xxxiii, 213.^f ----, ----, see farther under _Electro-Magnetic_ and _Magneto-Electric_. ----, musical tones from, _C. G. Page_, xxxii, 396; xxxiii, 118; xlviii, 401. ----, cause of voltaic currents with, _J. P. Emmet_, xxvi, 23.^f ----, native, in Rhode Island, iv, 285; v, 402. Magnetic attraction and repulsion, law of, _R. W. Fox_, xxviii, 370. ---- ---- ---- reciprocating motion of, _J. Henry_, xx, 340.^f ---- chart, of the U. States, _E. Loomis_, xxxiv, 290; xxxix, 41. ---- compass, mariner's, on the invention of, _A. Humboldt_, xl, 242. ---- dip, in different parts of the world, _T. H. Perry_, xlvii, 84. ---- ----, at different places in Europe, xl, 30. ---- ----, in Ireland, _H. Lloyd_, xxxv, 296. ---- ----, at Perth, Scotland, xl, 342. ---- ----, at St. Petersburg, xxi, 382. ---- ----, at different places in the U. States, xl, 380. ---- ----, ibid, _J. Locke_, xxxix, 319; xl, 149; xli, 15. ---- ----, ----, ibid, remarks on, xxxix, 325. ---- ----, ibid, _E. Loomis_, xxxiv, 290^f; xxxix, 41^f; xl, 85. ---- ----, at various places in Ohio and Michigan, _E. Loomis_, xxxviii, 397. ---- ----, ---- ibid, at Cincinnati, _J. Locke_, xl, 56. ---- ----, at Philadelphia and Baltimore, _A. D. Bache_, xl, 375. ---- ----, at Baltimore, _J. Locke_ and _J. N. Nicollet_, xlii, 239. ---- ----, at Nantucket, _W. Mitchell_, xlvi, 157. ---- ----, daily variation in, _Kupffer_, xxv, 194. ---- ---- and intensity determined by one instrument, _H. Lloyd_, xxxviii, 179. ---- discoveries by _H. H. Sherwood_, xxxiv, 210. ---- effects from Hare's calorimotor, _G. T. Bowen_, v, 357. ---- experiments, showing the effect of cold and heat on steel bars, _Kupffer_, xxv, 194. ---- influence of the sun's rays, xiii, 188; xviii, 181. ---- ---- of the violet ray, xviii, 171. ---- instrument, new, called a Solar Index, _M. Conant_, xlix, 301.^f ---- iron, see _Iron_. ---- intensity, at great elevations, _J. D. Forbes_, xxxi, 369. ---- ----, at different places in Europe, xl, 30. ---- ----, in Ireland, _H. Lloyd_, xxxv, 296. ---- ----, daily variation and changes in, _H. Lloyd_, xlvi, 391. ---- ----, in different places in the United States, xl, 378. ---- investigations, by _W.