416 



SCIENCE 



[N. S. Vol. XL VI. No. 1191 



By means of an electromagnet with a lamin- 

 ated core the magnetite crystal was magnetic- 

 ally saturated, and then demagnetized with an 

 alternating current. The effect of magnet- 

 ization perpendicular to the plane of the crys- 

 tal face was investigated for the first four 

 orders. On account of mechanical diSicultiea 

 the test was made only in the third order when 

 the crystal was magnetized parallel to the re- 

 flecting surface. In no case was any change 

 observed in the intensity of the reflected beam 

 when the crystal was magnetized or demag- 

 netized, though the method was sufficiently 

 sensitive to detect a variation in the intensity 

 of less than 1 per cent. 



A direct calculation shows that a displace- 

 ment of the atoms of 0.004 of the distance 

 between the successive atomic layers is suffi- 

 cient to cause 1 per cent, change in the inten- 

 sity of the fourth order spectrum. If there 

 is any displacement of the atoms when a 

 crystal is magnetized, it is therefore very 

 small. This confirms the observation of K. T. 

 Compton and E. A. Trousdale^ that magneti- 

 zation does not shift the atoms in a crystal 

 sufficiently to change the general form of the 

 space lattice in which they are arranged, and 

 verifies their conclusion that the ultimate 

 magnetic particle is not a group of atoms, 

 such as the chemical molecule, but is the in- 

 dividual atom or something within the atom. 



It can be shown further that if all the elec- 

 trons in an atom are in the same plane, the 

 effect on the intensity of the reflected X-ray 

 beam of turning the atom will be greater than 

 one per cent, unless the effective radius of 

 the atom is less than lO-^" cm. Other con- 

 siderations, however, prove that the radius of 

 the atom must be much greater than this. 



There is a relatively small number (26) of 

 electrons in the iron atom, and it appears 

 probable that 8 of these, as valence electrons, 

 are at a considerably greater distance than the 

 others from the center of the atom. It is 

 therefore difficult, though perhaps not im- 

 possible, to imagine an arrangement of the 

 electrons so isotropic that a rotation of the 



2 K. T. Compton and E. A. Trousdale, Phys. 

 Bev., 5, 315 (1915). 



atom will not produce an appreciable change 

 in the intensity of the reflected X-ray beam. 



The most obvious explanation of our nega- 

 tive result is that it is not the atom which is 

 the elementary magnet, but that it is either 

 the positive nucleus, as suggested by Merritt, 

 or the electron, as suggested by Parson. 



If the ultimate magnetic particle is not 

 rotated to any great extent by the magnetic 

 field, no conclusions can be drawn from our 

 experiments. It appears much more probable 

 however, that the molecular magnet is capable 

 of being turned through a large angle, and on 

 this basis we may conclude that: 



1. The ultimate magnetic particle is either 

 the atom or something within the atom. 



2. If the atom is the ultimate magnet, its 

 electrons are not all distributed in the same 

 plane, as assumed by Bohr, but are arranged 

 very nearly isotropically. 



3. Our experiments are in accordance with 

 the hypotheses that the atomic nuclei or the 

 electrons themselves are the ultimate mag- 

 netic particles. 



In a subsequent paper we shall describe our 

 experiment in greater detail, and shall discuss 

 more -fully the significance of our negative 

 result. Arthur H. Compton, 



Oswald Eognley 



TJniversitt of Minnesota 



apparatus for physiological and 

 physical laboratories 



An Adjustahle Stand for Graphic Experi- 

 ments. — The stand illustrated in the figure 

 was designed by me, twenty-three years ago, 

 for use with the piston-recorder for air trans- 

 mission. It has served its purpose so admir- 

 ably, and is so well adapted for all graphic 

 work where a very delicate adjustment of the 

 writing point is required, that it has seemed 

 to merit a description in print. 



The features that have commended it es- 

 X)ecially are its simplicity, its great delicacy 

 of movement and absence of backlash, and 

 the ability to use it at all times for any of the 

 purposes for which a small stand is necessary. 



Its construction is not difficult, but requires 

 accurate workmanship. 



