1823 .J M. Schweigger's Electromagnetic Multiplier. 437 



tromagnetic multiplier is formed ; fig. 3 represents an apparatus 

 according to my construction, which differs, however, from 

 M. Schweigger's in no essential respects. A A, fig. 3, is the foot 

 of the apparatus. C C, C C, are two stands which support a 

 frame B B, which has a groove on the edge to receive the mul- 

 tiplying wire. DDis a stand to support the wire from which 

 the magnetic needle is suspended. E E is a metallic wire 

 passed tightly through a hole made in the upper part of the 

 stand D D. To this metallic wire there is attached by a 

 little wax a thread of raw silk E F, suspending a double trian- 

 gular loop of paper, in which the magnetic needle is placed. 

 E G is a tube which allows the suspension wire a free 

 passage, and prevents the multiplying wire from touching it. 

 Below the magnetic needle a divided circle is placed to measure 

 the deviations. The multiplying wire is of plated copper, and a 

 quarter of a millimetre, or about -pi^ of an inch in diameter. 

 It is covered with silk thread, which prevents any communica- 

 tion between the different parts of the multiplying wire ; H and 

 J are the two ends of this wire. The use of this apparatus will 

 be understood almost without any explanation. In order to 

 multiply the effect produced by a galvanic arrangement upon the 

 needle, it is requisite only to effect a communication so as to 

 make the multiplying wire a part of the circuit. The effect of 

 a disk of copper and of zinc with pure water as a liquid conduc- 

 tor, was rendered perfectly sensible by this apparatus, and 

 it is even possible by its means to render those galvanic actions 

 sensible, which are too weak to produce a marked effect upon 

 the prepared muscles of a frog. When it is required to discover 

 an action which is so extremely weak as to occasion a scarcely 

 visible deviation, the circuit is interrupted immediately after it 

 has been completed, but it is again effected at each time that 

 the needle is at the point of terminating the preceding oscil- 

 lation ; the apparatus may be rendered still more sensible by 

 putting a small magnetic needle in H H in the situation re- 

 quired to diminish the force with which the suspended needle 

 tends to preserve its direction. 



When the multiplier is employed for moderately strong elec- 

 tromagnetic action, thicker conducting wires must be used. If 

 this precaution be neglected, the effect may be diminished 

 instead of increased, owing to the imperfection of the conductor. 

 M. Seebeck has made some very satisfactory researches on this 

 subject, in his memoir on electromagnetism, published two 

 years since in the memoirs of the Berlin Academy. 



M. Poggendorf, of Berlin, a distinguished young philosopher, 

 constructed an electromagnetic multiplier very soon after M. 

 Schweigger, and made some striking experiments with it. 

 The experiments of M. Poggendorf having been cited in a work 

 upon electromagnetic phenomena by the celebrated M. Erman, 

 published soon after the discovery of these phenomena, were 



