CONTEMPORARY ADVANCES IN PHYSICS 365 



recoil from the spinning electrons is detectable. This seems to be 

 as yet the only contribution of ferromagnetism to contemporary 

 atomic theory. 



Yet even if we take it for settled that the elementary magnets 

 within the atoms of a solid piece of iron are spinning electrons, the 

 real problem of ferromagnetism remains unsolved. If the elementary 

 magnets in iron are just like those in all other atoms, how does it 

 happen that iron and two other elements alone may be ferromagnetic? 

 that even iron may cease to be ferromagnetic, if mixed with a little 

 manganese? that manganese and copper and aluminium can become 

 ferromagnetic when and only when alloyed together? Since appar- 

 ently we must not suppose that each atom of iron is distinguished 

 from all those of never-ferromagnetic substances through having a 

 peculiar kind of magnet inside it, we must suppose that something 

 strange in the arrangement of the electron-magnets of the iron atom 

 permits it to be so distorted, and so to distort its neighbors, that 

 on occasion its neighbors and itself jointly develop ferromagnetism. 

 There is something extraordinary about the systems of 26 and 27 and 

 28 electrons about a nucleus, which iron and nickel and cobalt atoms 

 are. Their individual electrons are not unique; by themselves, or as 

 ions in a solution, they show nothing unique; but they turn into some- 

 thing unique when they are rightly compounded together into a solid. 

 The theories of ferromagnetism and the gyromagnetic effect have 

 limited without solving the fundamental problem of ferromagnetism: 

 what is it that makes the difference between the ferromagnetic sub- 

 stances, and all the rest? 



Acknowledgments and References 



The foregoing article is based largely upon the books of J. A. Ewing {Magnetic 

 Induction in Iron and Other Metals; Electrician, 1900), P. Weiss and E. Foex {Le 

 Magnetisme; Colin, 1926) and E. C. Stoner {Magnetism and Atomic Structure; 

 Methuen, 1926); the articles by S. Bidwell in the eleventh edition of the Encyclo- 

 paedia Britannica, by P. Debye in volume 6 of the Handbuch der Radiologic, by E. 

 Gumlich and R. Cans in Die Kultur der Cegenwart, by K. Honda in the Dictionary of 

 Applied Physics; and the articles of L. W. McKeehan on ferromagnetism {Journ. 

 Franklin Inst. 197, pp. 583-602, 757-786; 1924), magnetostriction {ibid. 202, pp. 

 737-773; 1926) and the permalloys {Phys. Rev. {2) 28, pp. 146-166; 1926, and others 

 there cited). 



Some of the very recent papers upon magnetization of single crystals are those 

 of W. L. Webster {Proc. Roy. Soc. A107, pp. 496-509; 1925); K. Honda and S. 

 Kaya {Tohoku Univ. Sci. Rep. 15, pp. 721-753; 1926); W. Gerlach {ZS.f. Phys. 38, 

 pp. 828-840; 1926). For magnetostriction of single crystals, see W. L. Webster 

 {Proc. Roy. Soc. A109, pp. 570-584; 1925) and K. Honda and Y. Mashiyama {Tohoku 

 Univ. Sci. Rep. 15, pp. 755-776; 1926). For the data concerning permalloys see, 



