— —, polarity and dip of, a remark on, xxix, 353.
— —, made to indicate the true north, xxvi, 90.
— —, on the connexion of the theory of the earth with the secular variations of, J. H. Lathrop, xxxviii, 68.
— needles, best position of three, for mutual action, H. Lloyd, xxxviii, 96.
— observations, a union of effort urged for carrying on, xviii, 380.
— —, great scheme for, by the Royal Society of London, xxxvii, 198.
— —, ibid, by British Association, xl, 335; xlii, 151; xliii, 374.
— —, in Russia and other countries, in progress, xlii, 153.
— —, coöperation of the Amer. Acad. of Arts and Sciences in a general system of, xxxix, 193.
— —, corresponding, by A. D. Bache and H. Lloyd, xli, 260.