370 



j\Ir. Wlieatstone on the Augmentation [Feb. 14^ 



cuit, in which the currents generated by the armature, after being changed 

 to the same direction, act so as to increase the existing polarity of the elec- 

 tro-magnet, very different results will be obtained. The force required to 

 move the machine will be far greater, showing a great increase of magnetic 

 power in the horseshoe ; and the existence of an energetic current in the 

 wire is shown by its action on a galvanometer, by its heating 4 inches of 

 platinum wire *0067 in diameter, by its making a powerful electro -magnet, 

 by its decomposing water, and by other tests. 



The explanation of these effects is as follows : — The electro-magnet 

 always retains a slight residual magnetism, and is therefore in the condition 

 of a weak permanent magnet ; the motion of the armature occasions feeble 

 currents in alternate directions in the coils thereof, which, after being re- 

 duced to the same direction, pass into the coil of the electro-magnet in 

 such manner as to increase the magnetism of the iron core ; the magnet 

 having thus received an accession of strength, produces in its turn more 

 energetic currents in the coil of the armature ; and these alternate actions 

 conthme until a maximum is attained, depending on the rapidity of the 

 motion and the capacity of the electro-magnet. 



If the two coils be connected in such manner that the rectified current 

 from the coil of the armature passes into the coil of the electro-magnet in 

 the direction which would impart a contrary magnetism to the iron core, 

 no current is produced, and consequently there is no augmentation of mag- 

 netism. 



It is easy to prove that the residual magnetism of the electro-magnet is 

 the determining cause of these powerful effects. For this purpose it is 

 sufficient to pass a current from a voltaic battery, a magneto-electric ma- 

 chine, or any other rheomotor, into the coil of the electro-magnet in either 

 direction, and it will invariably be found that the direction of the current, 

 however powerful it may eventually become, is in accordance with the po- 

 larity of the magnetism impressed on the iron core. 



If, instead of the currents in the coil of the rotating armature being re- 

 duced to the same uniform direction, they retain their alternations, no effects, 

 or at most very small differential ones, are produced, as no accumulation of 

 magnetism then takes place. 



I will now call attention to the fact that stronger effects are produced at 

 the first moment of completing the combined circuit than afterwards. 

 The machine having been put in motion, at the first moment of completing 

 the circuit 4 inches of platina wire were made red-hot, but immediately 

 afterwards the glow disappeared, and only about one inch of the wire could 

 be permanently kept at a red heat. This diminution of effect was accom- 

 panied by a great increase of the resistance of the machine. The cause of 

 the momentary strong effect was, that the machine from its acquired mo- 

 mentum continued its motion for a few seconds, though it required a 

 stronger force than could be applied to maintain that motion. Each time 

 the circuit is broken and recompleted the same effect recurs. 



