Ixiv GENERAL SUMMARY OF SCIENTIFIC AND 



Jamiii has published an extended paper on magnetism, in which 

 he gives the laws of magnetic distribution. 



Duter has studied the distribution of magnetism in circular and 

 elliptic steel plates, and concludes, 1st, the free magnetism is pro- 

 portional to the surfaces ; 2d, it is distributed in hyperbolic lines, the 

 non-transverse axes of which are in the direction of the axes of sym- 

 metry perpendicular to the neutral line. 



Gaugaiu, in a paper on the jDrocesses of magnetization, has stated 

 that wdien two magnets have their contrary poles jDlaced in contact 

 with a bar near one of its ends, their action to develop magnetism 

 temjDorarily at the middle point of the bar is very unequal, while 

 the permanent magnetism thus produced is stronger at this middle 

 point when but a single magnet is used. He gives theoretical con- 

 siderations in explanation of these phenomena. 



Gaugain has also studied the influence of the temper of steel upon 

 its magnetization. As a result of his experiments, he concludes that 

 those bars which have received the hardest temper are those which 

 take the strongest magnetization when powerful means are em- 

 ployed to develop it, but that annealed bars are magnetized more 

 strongly by means which are less energetic. 



Fave has experimented on the action of heat on the magnetism 

 of steel bars, with special reference to the observation of Jamin that 

 steel is capable of receiving a considerable magnetism at a tempera- 

 ture at which it loses entirely all magnetism which it has received 

 when cold. He finds, 1st, that the magnetism of a bar may be pre- 

 served at any temperature whatever, if this temperature be main- 

 tained constant ; 2d, that the diminution of the magnetism, at first 

 slow, becomes very rapid at the end of a time varying with the tem- 

 perature of magnetization ; and, 3d, the magnetism which remains 

 after cooling, increases again upon heating the magnet. 



Cazin has sought to establish a relation between the heat pro- 

 duced by the magnetization and the demagnetization of iron, the 

 amount of magnetism alternately lost or gained by the core and the 

 position of the poles, and in this way to get an ajoproximate value 

 for the magnetic equivalent of heat. 



Duchemin has proposed the use of nickel for the protection of 

 the needles of marine compasses against rust, and he gives the results 

 of some experiments in this direction, made with his circular com- 

 pass, which were entirely satisfactory. The deposit of nickel does 

 not seem to affect appreciably the magnetization. 



Deprez has made some experiments on the velocity of magnetiza- 

 tion and demagnetization of iron, and finds that soft iron, ordinary 

 iron, malleable cast iron, and chilled steel all required one and a 

 half thousandths of a second for magnetization, and one four-thou- 

 sandth for demagnetization. Gray cast iron was magnetized in one 

 thousandth. 



