October 26, 1917] 



SCIENCE 



415 



eludes interesting sections on inorganic and 

 organic nomenclature. Many American chem- 

 ists should read and heed the translating rules 

 contained in these sections, for all too often 

 German spellings, especially endings, are car- 

 ried over into names used as English. At 

 times this results in confusion. The new dic- 

 tionary will tend to correct this bad practise, 

 and it is hoped that it will help the cause of 

 good chemical nomenclature in other ways. 



Besides words from fields of science related 

 to chemistry the dictionary contains a general 

 vocabulary " to save the user the trouble of 

 looking up the more common German words in 

 a separate dictionary " and " because many 

 general words have a technical, or at least a 

 customary, chemical meaning," which " in a 

 general work is often either absent or buried 

 among other senses." The entries are all 

 brief, few of them requiring more than a 

 single line (two columns to the page). There 

 are no long paragraphs of combinations, ex- 

 amples, etc., to wade through. The English 

 equivalent usually sought by the scientist is 

 given at once. These features add greatly to 

 the convenience in use. 



The use of small type (six point), which 

 does not seem objectionable since one does not 

 read a dictionary steadily, has made for com- 

 pactness. The book wiU fit a large pocket. 

 The work of the printer and binder (the cover 

 is flexible) has been well done. 



E. J. Crane 



Ohio State TJNrTERSiTT 



SPECIAL ARTICLES 



THE NATURE OF THE ULTIMATE 

 MAGNETIC PARTICLE 



It appears probable from various consid- 

 erations that when a substance is magneti- 

 cally saturated, the " molecular magnets " of 

 which it is composed have their axes arranged 

 parallel with the external magnetic field. On 

 this assumption it is possible to investigate 

 the validity of those theories, such as Bohr's 

 which would explain the magnetic properties 

 of an atom as due to electrons revolving about 

 the atomic center in orbits all lying in the 

 same plane. 



It has been shown that the relative inten- 

 sity of the different orders of an X-ray spec- 

 trum line depends upon the distance of the 

 electrons from the middle planes of the atomic 

 layers in the diffracting crystal.^ Imagine 

 X-rays to be reflected from the surface of a 

 ferro-magnetic crystal composed of atoms of 

 the type just described. When the crystal 

 is unmagnetized the difFerent atoms will have 

 their electronic orbits distributed in all pos- 

 sible planes, so that on the average the elec- 

 trons will be at an appreciable distance from 

 the mid-planes of their atomic layers. If, 

 however, the crystal is magnetically saturated 

 perpendicular to the reflecting face of the 

 crystal, the electronic orbits, being perpen- 

 dicular to the magnetic axes of their atoms, 

 will all lie parallel to the crystal face. The 

 electrons will therefore now be in the mid- 

 planes of the layers of atoms which are 

 effective in producing the reflected beam. It 

 can be shovm that such a shift of the elec- 

 trons must produce a very considerable in- 

 crease in the intensity of the reflected beam 

 of X-rays. On the other hand, if the crystal 

 is magnetized parallel to the reflecting face, 

 the turning of the orbits will carry the elec- 

 trons farther, on the average, from the middle 

 of their atomic layers, and a decrease in the 

 intensity of reflection should result. Of 

 course if the electrons are arranged isotropic- 

 ally in the atom, or if the atom is not rotated 

 by a magnetic field, which would mean that 

 it is the electron or the positive nucleus that 

 is the ultimate magnetic particle, no such 

 effect should be observed. 



We have hunted in vain for such an effect 

 on the intensity of the reflected beam of X-rays 

 when the reflecting crystal is strongly magnet- 

 ized. In our experiment a "null method" was 

 employed. The ionization due to the beam of 

 X-rays reflected from a crystal of magnetite 

 was balanced against that due to a beam re- 

 flected from a crystal of rock-salt, so that a 

 very small change in the relative intensity 

 of either beam could be detected, while vari- 

 ations in the X-ray tube itself had little effect. 



lA. H. Compton, Fhys. Ecv., 9, 29 (1917). 



