376 Prof .Oersted on new Electromagnetic Experimetits. [NoiV. 



passage for the negative electricity from z to c, and for the posi- 

 tive electricity from c to 2. We see then that the wire a b 

 receives the negative electricity of the zinc, and the positive 

 electricity of the copper, while a wire that constitutes the com- 

 munication of the two poles of a pile, or of another compound 

 galvanic apparatus, receives the positive electricity of the zinc 

 pole, and the negative electricity of the copper pole. 



By attending to this distinction, we may, with a single 

 galvanic arc, repeat all the experiments which I had at first 

 made with a compound galvanic apparatus. Employing a 

 single galvanic arc gives this great advantage, that it enables us 

 to repeat the experiments with little preparation and expense. 

 But it presents another advantage still more considerable ; 

 namely, that we may establish a galvanic arc sufficiently power- 

 ful for the electromagnetic experiments, and yet sufficiently 

 light to be suspended to a small metallic wire, in such a manner 

 that the small apparatus may be made to turn round the pro- 

 longed axis of the wire. We may in this way examine the 

 action which a magnet exerts on the galvanic arc. As a body 

 cannot put another m motion without being moved in its turn, 

 > when it possesses the requisite mobility, it is easy to foresee 

 that the galvanic arc must be moved by the magnet. 



I made use of different arrangements of the simple galvanic 

 apparatus to examine the motion impressed on it by the magnet. 

 One of these arrangements is represented in fag. 10, which repre- 

 sents a perpendicular section of it in the direction of the breadth. 

 ccc c is a trough of copper, three inches high, four inches long, 

 and half an inch broad. These dimensions doubtless may be 

 varied to infinity. It is only necessary to observe that the 

 breadth ought not to be great, and thus the trough should be 

 made of plates as thin as possible. 2 z is a plate of zinc. II are 

 two pieces of cork which keep the plats in its position, cj'fffz 

 is a brass wire, of a quarter of a hue at least in diameter, a o,is 

 a brass wire as fine as possible, so as to be able to bear the 

 weight of the apparatus, c a c is a linen thread uniting the 

 wire to the apparatus. The trough contains the liquid conduc- 

 tor. The conducting wire of this apparatus will attract the 

 north pole of the needle when it is placed on the left side of the 

 fl&ne cff ft z, considered in the direction /^. On the same 

 side the Sduth pole will be repelled. On the other side of this 

 plane, the north pole will be repelled, and the south pole 

 attracted. That this effect may take place, we must not place 

 the needle above^'^j nor below/" z or/' c. If instead of present- 

 ing a small moveable needle to the conducting wire we present 

 near one of the extremities yy" one of the poles of an energetic 

 magnet, the attraction or repulsion indicated by the needle 

 will put the galvanic apparatus in motion, and will turn it round 

 the prolonged axis of a b. 



If instead of the conducting wire we take a large ribbon of 



