108 DOVE ON THE ELECTRICITY OF INDUCTION. 



like direction to that excited in « /3 by the electrical current 

 existing in « A at the moment of its cessation. The equilibrium 

 of the currents which previously existed in « jS 7 S is therefore 

 also destroyed, but the resulting current, even for all methods 

 of trial, will exhibit an opposite direction, namely from a to- 

 wards (3 ; for now the augmented « B will preponderate over y 8 

 which has not been augmented. Let us suppose, lastly, the 

 electro-magnetized bar of iron sn surrounded by a conducting 

 wire efg h, then in consequence of the evanescent magnetism in 

 sn Q. larger quantity of electricity will be put in motion in the 

 wire a. /3 than in the wire y S ; but as an electric current is si- 

 multaneously excited in efgh this quantity of electricity will 

 move more slowly than the lesser quantity in the wire y 8. 

 Here three different cases are possible : 



1. The augmented quantity of electricity may increase 

 some particular action of the current more than the retar- 

 dation of the current diminishes it. 



2. The increased action caused by the augmentation of 

 the quantity of electricity may be exactly compensated by 

 the retardation of the current. 



3. The retardation of the current may diminish some par- 

 ticular action more than the augmentation of the quantity 

 of electricity increases it. 



In the first case, the current will be directed from « towards 

 /3 ; in the second, the equilibrium of the currents will remain sta- 

 tionary; and in the third, the current will flow from /3 to- 

 wards a. When the pi'imary current which magnetizes the iron 

 is that of a galvanic circuit, that of a thermo-battery or thermo- 

 circuit, or the induced current of a Saxton's machine, the first 

 case is always observed ; when however the primary cun-ent is 

 produced by the discharge of a Leyden jar or of an electrical 

 battery, the third case, and under particular circumstances 

 the second case happens ; but in such a manner, that when the 

 first case occurs for one method of testing the current, the third 

 case may occur for another method, and vice versa. Lastly, the 

 primary current of a Saxton's machine may be so modified by 

 the extra current which it produces, that all three cases may be 

 observed with it. 



A bundle consisting of insulated iron wires is not capable of 

 producing peripherical electrical currents surrounding the whole 

 of the bundle. If however it is inclosed in a conducting sheath. 



