6 REPORT — 1853. 



the distance from the magnet ; and, by having recourse to the law of electro-mag- 

 netism, he arrived at an explanation of the magnetism of rotation of M. Arago. The 

 author, after giving some further historical details, proceeded to point out how per- 

 plexing were the phsenomena arising from the abrupt and numerous changes of 

 direction. He then proceeds to state his own conception of the subject, and to 

 detail the experimental researches which he had founded upon them ; draws general 

 conclusions from the experiments ; and has drawn up a simple and perspicuous 

 diagram, indicating the poles of the magnet, the revolving disc, and the curves 

 which show the neutral points upon the disc, and those indicating the directions of 

 the tangential forces, or those giving to the disc the tendency to revolve, and all of 

 which he finds to have a fixed relation to the position of the poles of the magnet and 

 the velocity of the rotation. The memoir is to be published entire. 



On the Magnetism of Rotation in Masses of Crystallized Bismuth. 

 By Professor Matteucci, Pisa. 



The apparatus used by the author consisted of an electro-magnet caused to 

 revolve by clockwork ; and the body to be submitted to the action of the electro- 

 magnet was suspended between its poles. Sometimes he suspended it by a fine 

 silver wire, and determined the force of torsion, when equilibrium took place, the 

 body being usually suspended in water to check its tendency to vibrate. Sometimes 

 he used a single thread of cocoon silk, and the forces developed were measured by 

 counting the number of uniform rotations which took place in a given time. The 

 author first describes certain preliminary experiments which he made with this 

 apparatus. He suspended solid spheres of copper, and hollow spheric shells, of 

 exactly the same diameter, formed by the electro-plate process, between the revolving 

 poles, and measured the force by torsion. With a full sphere weighing 59'80gr., 

 and a hollow one weighing 10'85 gr., he found the torsions in the proportion of 

 1 :0*71. With spheres of a less size the differences were less than these. The 

 author concludes from this that the internal shells of metal, on which the induced 

 forces are less, serve to discharge the currents developed in the exterior shell ; and 

 that an analogous effect shows itself in many other cases of magnetism of rotation. 

 The author also submitted to the same apparatus a cube, formed of very thin square 

 laminae of copper, insulated from each other by layers of varnish ; when this cube 

 was suspended a few centimetres above the electro-magnet, so as to have its con- 

 stituent laminae horizontal, it experienced no action from the magnet; but when its 

 laminae were vertical it received a very rapid motion of rotation ; in this latter case 

 the currents induced having the power to develope themselves freely, and circulate 

 on each lamina, which cannot take ))]ace in the former case. In his experiments 

 with crystallized bismuth compared with amorphous masses of the same substance, 

 he found, — 1. That the forces developed by the revolving electro-magnet are greater 

 for the amorphous masses of bismuth than for the crystallized metal ; 2. that the 

 forces developed in the masses of crystallized bismuth are greater when the cleavages 

 are disposed vertically and perpendicularly to the planes of the currents of the 

 electro-magnet, than when these cleavages are placed horizontally. 



On tiie Magnetism of Rotation developed in very small Insulated Metaliic 

 Particles. By Professor Matteucci, Pisa. 



On Magnetic Phcenomena in Yorkshire. 

 By John Phillips, M.A., F.R.S., F.G.S. 



The author proposed, in this communication, to place on record some measures of 

 the direction of magnetism in Yorkshire, and some inferences touching the relation 

 of magnetism to the physical geography of the district. The magnetic declination 

 from the true meridian is at this time about 24° to the W. of North at York, and is 

 slowly diminishing. The magnetic inclination from the vertical, measured in the 

 plane of the magnetic meridian, is now at York 70° 10', and is diminishing about 

 2'*54 in a year. This result is obtained by comparing many careful observations 

 between 1837 and 1853. 

 . In tracing the lines of equal dip over the large area of Yorkshire, the author ems 



i 



