Oersted on Etectro-Magnethm. 125 



M. Schweigger, merely in parts not essential. AA is the foot of 

 the instrument ; CC,CC, are two uprights, which carry a frame BB, 

 in the border of which there is a groove, where the successive 

 turns of the multiplying wire lodge. DD is an upright, destined 

 to support the wire, from which the needle is to be suspended. 

 All these parts are of wood. EE is a wire of metal, which passes 

 with friction through a hole, pierced in the upper part of the 

 upright DD. To this, metallic wire is attached by a little wax, 

 the silk-worm thread EF ; the latter bears at its extremity a small 

 (folded) double triangle of paper, on which reposes the little mag- 

 netic needle. At G, is a hollow cylinder, in which the thread of 

 suspension passes freely, and which prevents the multiplying 

 wire from touching it. There may be seen also beneath the 

 needle, a graduated circle for measuring the deviations. The 

 multiplying wire is of silvered copper ; its thickness is one-fourth 

 of a millimetre (about 0.01 of an inch Eng.). It is wrapped 

 through its whole length in silk thread. Thus all electric commu- 

 nication is avoided between the different parts of this wire, which 

 are wound over one another in the groove of the frame B B. H and 

 J represent the two extremities of the wire. 



The use of this apparatus may be conceived almost without 

 explanation. To multiply the effect which a galvanic arrangement 

 has on the needle, the communications have only to be established, 

 so that the multiplying wire may become a part of the circuit. 

 The electricity developed by the contact of two discs, the one of 

 zinc, and the other of copper, when nothing but water is employed 

 for the liquid conductor, is perfectly appreciable with this appara- 

 tus. We may in the same way make galvanic actions manifest, which 

 would be too feeble to be perceived by employing a prepared frog. 

 When we wish to render evident an extremely weak action, which 

 gives a scarcely visible deviation, we must open the circuit imme- 

 diately after closing it, and then close it anew every time that the 

 needle is on the eve of terminating the return of the preceding- 

 oscillation. The apparatus may be also rendered more delicate by 

 placing in HH a small magnetized needle, in the position requisite 

 for diminishing the force with which the suspended needle tends 

 to preserve its direction. When it is wished to make use of the 

 multiplier for electro-magnetic actions somewhat more consider- 

 able, much thicker conducting wires must be employed. Without 

 this precaution, there might be, instead of an increase, a dimi- 

 nution of effect, caused by the imperfection of the conductor. 

 M. Poggendorff has made a happy application of the multiplier to 

 examine the order of the conductors in the galvanic series. He 

 found also that some metals gave, at the instant of their being 

 plunged into concentrated nitric acid, an effect contrary to what is 

 manifested some moments afterwards. This change does not take 

 place with dilute nitric acid. The metallic couples which shewed 



