Intelligence and Miscellaneous Articles. 331 



COMBINATION OF AN EXPERIMENT OF AMPERE WITH AN 



EXPERIMENT OF FARADAY. BY J. J. TAUDIN CHABOT. 



It was shown by Ampere * how a magnet can be made to rotate 



about its axis under the influence of a steady current, and Faraday f 



showed how the rotation of a magnet about its axis can give rise 



to a steady current +. 



By combining these two experiments we obtain a case of 

 induction by steady currents : a steady primary current in the 



circuit E or E x gives rise to a steady secondary current in the 

 circuit E x or E, a rotating magnet M forming the connecting link. 



In order to show the effect, a brake is applied to the magnet M, 

 a battery is inserted into the circuit E or E 2 and a galvanometer 

 into the other circuit E 3 or E. On closing the circuit we observe 

 that the suspended system of the galvanometer remains at zero ; 

 but, on removing the brake from the magnet, this begins to rotate 

 and the galvanometer shows a deflection which increases con- 

 tinuously until the magnet turns quite freely. A brake is desirable 

 which admits of a graduated application. 



It appears to me that this experiment is worthy of notice in 

 consideration of its illustrative character §. 



Degerloch (Wiirttemberg), 

 December 12th, 1898. 



EXPERIMENTS WITH THE BRUSH DISCHARGE. 

 To the Editors of the Philosophical Magazine. 



Gentlemen, 



I have read with considerable interest the paper by Dr. Cook 

 on the " Brush Discharge " in the January number of your 

 Magazine. May I be allowed to call attention to some experiments 

 made by Lord Blythswood about two years ago, which are of a very 



* Recueil d? Observations, p. 177 (1821). Lettre a M. van Beck. 



t 'Experimental Researches/ series ii., §§ 217-230 (1832); see also 

 series xxviii. (1851). 



X This phenomenon is generally known by the name of " unipolar '' 

 induction ; " autopolar " induction (induction autopolaire, Gleichpolin- 

 duction), it seems to me, would be better; and therefore 1 propose this 

 term. Then, in contradistinction, " heteropolar " induction (induction 

 he"teropolaire, Wechselpolinduction) can be used for signifying induction 

 by both the poles alternately (dynamo &c). 



§ See Phil. Mag. vol, xlvi. p. 428 (Oct, 1808)., and p. o71 (Bee. 1898). 



