316 Intelligence and Miscellaneous Articles. 



demonstration by Messrs. Ayrton, Mather, and Sumpner in their 

 original paper. It may be well, however, to note that this con- 

 clusion does not vitiate the inferences which were the main point 

 of my former paper, namely, the comparative inefficiency of the 

 central portion of the coil, even if wound in reverse order, and the 

 consequent importance of employing exceedingly short needles. 



Silas W. Holman. 

 Boston, Mass., February 18, 1897. 



ON MAGNETIC AFTER-ACTION. BY PROF. IGN. KLEMENCIC. 



The magnetic induction which is observed in soft iron wires 

 which have been annealed for some time, and are placed in weak 

 fields, is made up of two parts : a fact established by Ewing 

 (Phil. Trans. 1885, p. 569, and Proc. Eoy. Soc. L889) and Lord 

 Eayleigh (Phil. Mag. 1887). One part follows the production or 

 cessation of magnetizing force ; the second part begins after the 

 termination of the former, and develops itself very slowly, so that 

 the intensity of magnetization attains its final value only after 

 some minutes. The phenomenon of a time retardation was 

 denoted as "creeping" or viscous hysteresis; it is here called 

 " magnetic after-act ion." It is very probable that the establishment 

 of magnetic after-action in the middle of the wire proceeds more 

 rapidly than at the ends. 



Magnetic after-action occurs mostly in weak fields ; it diminishes 

 with the strength of the field, and the more rapidly the thinner 

 the wire under investigation. 



No regular connexion between the magnetic after-action and the 

 thickness of the wire could be made out, probably owing to unequal 

 annealing. 



Strong magnetizations of the wires in no wise affect their mag- 

 netic after-action. 



Magnetic after-action is a transitory phenomenon, which is only 

 observed in freshly-annealed bars. — Wiener Berichte, March 1897. 



MAGNETIC INFLUENCE ON LIGHT-FREQUENCY. 



The footnote on page 232 (March no.) was by the communicator, 

 not the author, of the paper ; and he notes that the simplest way of 

 putting the elementary theory, for an ion or electron revolving in 

 an orbit of fixed size but any shape, is to write the radial magnetic 

 force as 



d(inrw 2 )— eBw, 



whence 2nn=duj = e^/2?n, 



n being the magnetically-caused change of frequency, and B the 

 density of magnetic induction, or /jH. — Ens. 



