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XXX. Intelligence and Miscellaneous Articles. 



OX A DAMPING ACTION OF THE MAGNETIC FIELD ON KOTATING 

 INSULATORS. BY WILLIAM DUANE. 



TT results from the experiments described by the author, that if 

 -*- an insulator is made to rotate in a magnetic field about an axis 

 at right angles to the lines of force, a damping action is exerted 

 in opposition and nearly proportional to the angular velocity. 



If the insulator is paramagnetic, such an action might be ex- 

 plained on the assumption that the magnetic axis of the insulator 

 does not coincide with the mngnetizing force of the field, but is 

 displaced in the direction of the rotation. A somewhat more 

 general assumption sufficing for the explanation is, that for an 

 insulator at rest the induced magnetism does not yanish at once, 

 but after an appreciable time. If it vanishes very rapidly we get 

 the proportionality observed between the damping force and the 

 velocity. 



For a diamagnetic insulator with true diamagnetic polarity the 

 corresponding assumption would give a force accelerating the rota- 

 tion. Nevertheless, according to several theories of diamagnetism, 

 even a diamagnetic body has paramagnetic polarity. According 

 to such theories the explanation given applies also to diamagnetic 

 bodies. — Wiedemann's Annalen, No. 7, 1896. 



THE ACTION OF MAGNETISM ON ELECTROMOTIVE FORCE. 

 BY ALFRED H. BUCHERER. 



The results of this investigation may be stated thus : — 



1. In neutral ferrous salts, if one of the two equal iron elec- 

 trodes is magnetized, there is no electromotive force produced 

 which amounts to 0-00001 volt. The currents observed by Gross 

 and others could not be referred to a change of the electrochemical 

 potential of the magnetized iron. 



2. The forces produced by magnetizing a circuit which contains 

 magnetic substances as electrodes are to be ascribed to variations 

 of concentration which the magnetized electrode produces when 

 dissolved. 



3. In the case of ferric salts, the direction of the currents pro- 

 duced by magnetization depends almost exclusively on their degree 

 of concentration at the two electrodes. 



4. If only ferrous salts are present, the direction of the currents 

 produced by magnetization depends on the total concentration of 

 the iron salts. 



5. The currents designated by Eowland as primary ones are 

 agitation-currents. — Wiedemann's Annalen, No. 7, 1896. 



