The results obtained by the author, described in a former communication, when a copper disc was made to revolve under a magnetized needle, appearing to him not likely to lead to an accurate knowledge of the law of magnetic attraction, developed during rotation, from the effect of lateral attraction; he was induced to resume the inquiry, substituting a ring for a disc, expecting that, as no lateral forces would here be called into action, the results would be more uniform, and in this expectation he was not disappointed. One of the first phenomena encountered by him in this research, was a very great diminution of magnetic force, when a ring of the same weight was substituted for a disc; and pursuing this point of inquiry, he found that in all cases of solution of continuity, not only by cuts in the direction of radii from the centre, but in concentric annuli or otherwise, there is always a great loss of force, the magnetism of the whole being always much greater than the sum of that of the parts. He describes in detail these experiments, and the apparatus used for them. His method of estimating the intensity of the force developed, was by suspending the body, set in, rotation by a revolving magnet, by a wire, and preserving a constant velocity of rotation in the magnet, to note the time when the velocity acquired by the disc, was just destroyed by the torsion of the wire, and the disc just began to revolve in a contrary direction. Applying analysis to the dynamical problem arising, he thence deduces the intensity of the force urging the suspended body. Applying the resulting formula to the experiments, he finds, in almost ail cases, a small diminution in the intensity of the force as the arc of rotation increases, which he attributes to a very minute degree of magnetism accumulated in the disc, and retained by it till the revolving magnet comes round again. In reasoning on the experiments detailed, Mr. Christie concludes that the greatest developement of magnetism in a disc, subjected to the action of revolving magnets, takes place when the axes of the magnets are vertically under points bisecting the radii, and that the magnetism decreases very rapidly as they approach the edge; thus indicating that for a full development of magnetism, a continuity of substance, in all directions from the point acted on, is principally requisite. This result is corroborated in a striking manner by the effect produced by concentric circular cuts in the disc, leaving the interior attached to the exterior in several places. On successively destroying these points of connexion, a very great diminution of force is perceived.