SCIENCE 



FRroAY, October 14, 1921. 



Magnetic Susceptibilities: Professor S. R. 

 Williams 339 



Fundamental Principles established Tjy Recent 

 Soil Investigations: Dr. Milton Whitney. 348 



Scientific Events: 

 The Council Meeting of the American Cliem- 

 ioal Society; The Optical Society of 

 America; The Southwestern Division of the 

 American Association for the Advancement 

 of Science; The Toronto Meeting of the 

 American Association for the Advancement 

 of Science 351 



Scientific Notes and News 353 



University and Educational Neivs 355 



The Causes of Whiteness in Hair and Feath- 

 ers: Dr. R. M. Strong. Sidewallc Mirages: 

 Allen P. Odell. Discovery of a Prehistoric 

 Engraving representing a Mastodon: Jay L. 

 B. Taylor. Some Suggestions for Photo- 

 graphing Fossils: Dr. Maurice G. Mehl. . . 356 



Scientific Books: 

 Sarrow on Vitamines: Dr. Percy G. Stiles. 358 



Experiments on the Recording aiid Reproduc- 

 tion of Cardiac and Respiratory Sounds: 

 Dr. Franklin L. Hunt and Captain Mag- 

 nus J. Myers 359 



Special Articles: 



The Separation of the Elements Chlorine 

 and Mercury into Isotopes: Professor Wil- 

 liam D. Harkins. .4?!. Artificial Nerve: Dr. 

 Reynold A. Spaeth 359 



The American Philosophical Society 362 



MSS. intended for 'publication and books, etc., intended for 

 review should be Bent to The Editor of Science, Garrison-on- 

 Hudson, N. Y. 



MAGNETIC SUSCEPTIBILITIES! 



A. Olassification of Bodies, Magnetically. — 

 1. Let us assume that we have at our disposal 

 a uniform magnetic field whose intensity, H, 

 and direction we can vary at will. H will 

 be expressed in Gauss and may be graphically 

 represented by drawing through a unit area 

 a number of parallel lines numerically equal 

 to H. Into such a field of force we may intro- 

 duce any substance we wish and study the 

 effects which that substance may produce on 

 the number of lines of force which thread 

 through the space we call the magnetic field. 

 Experimentally we find that any substance 

 when brought into a uniform magnetic field 

 causes a perturbation of the lines of force, 

 the character of which separates all substances 

 into two classes, viz., dia- and paramagnetic 

 bodies. The lines of induction are a con- 

 tinuation of those of the field, but in the case 

 of a paramagnetic substance are more closely 

 packed together, while in a diamagnetic body 

 they are further apart. Ferromagnetic sub- 

 stances are special cases of paramagnetism 

 of which the lines of induction are, relatively, 

 very closely packed together. A comparison 

 with the electric currents would make this 

 idea more precise. 



Suppose a sphere of metal introduced into a 

 mass of mercury traversed by a uniform current: 

 the lines of flow which were originally parallel 

 would tend to pass in greater number through the 

 sphere if it were a better conductor than the 

 mercury, and, on the contrary, in smaller number 

 if it were a worse conductor. The words con- 

 ductivity for lines of flow and permeability for 

 lines of magnetic induction thus correspond to 

 analogous ideas. 



If we let B represent the number of lines 

 of induction threading through unit area in 



1 Read before a joint meeting of the American 

 Physical Society and Section B of the American 

 Association for the Advancement of Science, De- 

 cember, 1920. 



