288 Historical Sketch of Electro-magnetism. [Oct. 



used only two plates, four inches square. The effects were very 

 strong on the magnetic needle. M. Schweiger opposes M. 

 Oersted's theory, and advances one of his own. 



In the same number of the Bib. Univ. M. de la Rive describee 

 the construction of two small apparatus, intended to show two 

 of the experiments made by Ampere, the attraction of an elec- 

 trical current by a magnet, and his artificial electro-magnet. 

 The first is made of two slips, one of zinc, the other of copper, 

 passing through a cork float, and connected above by a copper 

 wire curved. When this apparatus is placed on the surface of dilute 

 acid with the lower parts of the slips immersed, a voltaic combi- 

 nation is formed, which may be attracted and repelled by bringing 

 a magnet in different directions towards the connecting copper 

 wire above : fig. 12. The other is a zinc and copper plate, floated 

 on a cork as before, but connected above by a helix. This 

 helix is made by wrapping a copper wire covered with silk 

 round a small glass tube ; then slipping it off from the tube, 

 making the ends of the wire return through the helix till near 

 its middle, and then passing to the outside between the curves 

 of the helix ; they are then connected with the ends of the zinc 

 and copper slips ; and on the instrument being placed on the 

 surface of acidulated water, the ends of the helix will be 

 attracted and repelled, like the poles of a magnet: fig. 13. 

 These apparatus are very simple, easily made, and effectual. 



M. Moll, in three letters to the Editor of the Journal de Phy- 

 sique, the first dated March 23, the others without date, gives 

 an account of some experiments made to ascertain the relative 

 power of a battery consisting of many small plates, and one of 

 two large plates only. The large apparatus consisted of a narrow 

 trough of copper, containing a plate of zinc, presenting near four 

 square feet of surface. The smaller apparatus was one consist- 

 ing of plates, four inches square, put together in Dr. Wollaston's 

 manner, with the copper round the zinc. With the large appa- 

 ratus, M. Moll remarked, that the magnetic power was very 

 great, when the connecting wire was of considerable thick- 

 ness (2-10ths of an inch) ; but when a platina wire much smaller 

 was used (]-100th of an inch), the power diminished considera*- 

 bly. With a copper cylinder, however, about one inch in 

 diameter, the power was diminished. No chemical action could 

 be obtained by this apparatus on making the connection with 

 saline solutions, or tincture of litmus, though the magnetic effects 

 were very powerful. In making the comparison between this 

 apparatus and that with small plates and cells, 36 pair of the 

 latter were taken ; so that an equal surface of zinc was used in 

 both instruments. These being put into action by the same 

 acid, and the connecting wires being similar, that of the two 

 plates made the needle deviate from 60° to 70° from the magnetic 

 meridian ; while that of the small plate battery made it deviate only 

 12°. The decomposing power of the small plate battery was 



