124 



Progress of Foreign Science. 



for displaying, by means of the magnetic needle, the feeblest 

 electrical currents. The effect of this multiplier is founded on 

 the equal action exercised on the needle by all the parts of a 

 conducting wire, when it transmits a current. When a portion of 

 this wire is bent, like ab c, (Fig. 1.), if the two branches a b and 

 b c are in a vertical plane, and if a needle d e is suitably suspended 

 in the same plane, we may easily conceive, that the needle must 

 receive an impulsion double of what one of those branches would 

 have communicated. In fact, the impulsions given to the needle 

 by the two horizontal portions of the wire are added together. 

 To be satisfied of this, we have merely to observe, that in the 

 actual arrangement, these portions are percurned by the electrical 

 current in two different directions. The upper wire, and the under 

 wire cause the declination of the needle to the two opposite sides 

 only in the case where electricity moves in it, in the same direction. 

 We shall therefore increase the effect by giving the conducting wire 

 several convolutions round about the needle, as is shewn in Fig. 2. 

 It is this which constitutes the electro-magnetic multiplicator. 



Fig. 2. 



■ W=Sk 



Fig. 3. represents this apparatus according to the form which 

 M. Oersted has given it, which however differs from that of 



