500 



Sir J. A. Ewing on a New 



unequally in different atoms, with the effect of irregularly 

 augmenting the control, so that the metal becomes much less 

 easily magnetized and the curve of magnetization assumes a 

 more rounded form with less sharply separated stages, as is 

 in fact observed. Similarly, when atoms of foreign matter 

 have to find places in the space-lattice the symmetry of 

 the neighbours will be affected, and we may expect the 

 Weber elements in them to be in consequence unduly 

 stabilized. This is borne out by the fact that the hysteresis 

 of iron becomes in general less and its susceptibility 

 greater the more completely all impurities are eliminated. 

 Again, in a chemical compound of a ferromagnetic metal, 

 say iron, the distortion of the iron atom which comes of 

 its being unsjmmetrically surrounded may cause its mag- 

 netic properties to differ widely from those of an atom of 

 uncombined iron, and may be associated with the magnetic 

 seolotropy which is conspicuous in the crystals of certain 

 compounds. 



The form of model described above is based on the 

 Lewis-Langmuir type of atom. It is appropriate if the 

 electrons are conceived to have orbits that are small in 

 relation to the size of the atom, or to be small rings. But 

 the same principles may be equally well embodied in a model 

 that is based on the Bohr type of atom, with large electron 

 orbits. The conditions to be satisfied are these : that a 

 turning part, made up of one or more of the orbits with an 

 unbalanced magnetic moment, should be capable of orienta- 

 tion by an impressed field, but under magnetic controls 

 exerted by other parts of the atom, which are held relatively 

 fixed ; that it should deflect through no more than a very 

 small angle before becoming unstable ; that it should then 

 fall over with dissipation of energy into another position of 

 stability; and further that the stability in each stable 

 position should be weak. These conditions are satisfied when 

 the control depends on a balance of strong but oppositely 

 directed moments. They are realized in the model of figs. 

 4 and 5. 



There A and B. (fig. 4) represent coplanar elliptic orbits 

 with a common focus at the nucleus of the atom, which is 

 also the centre of a circular orbit W representing the Weber 

 element. The plane of A and B is to be thought of as fixed: 

 the plane of W may turn. In the model (fig. 5) the elliptical 

 controlling coils which correspond to A and B are set as 

 nearly as may be in one plane, and W is a circular coil 

 pivoted about a diameter ab. A margin of stability can 

 be given by making one of the fixed coils act rather more 



