282 Historical Sketch of Electro-maguetism. [Oct. 



employed was so simple and efficacious that they will make the 

 experiments come within the observation of those who may 

 otherwise think them too difficult to be easily performed. One 

 was simply aplatina crucible with a bent plate of zinc connected 

 with the bottom, and then passing off from the side, and turned 

 round till it dipped into the crucible, fig. 10. When diluted acid 

 was put into the crucible, the apparatus acted powerfully on the 

 ■magnetic needle. Another apparatus was formed from a small 

 gilt spoon having a bent slip of zinc attached to the handle, and 

 clipping into the bowl of the spoon. It acted very powerfully. 

 A third was a needle formed of a piece of zinc and a piece of 

 silver in the manner of a simple voltaic circle. This, fixed in 

 cork, and placed in diluted acid, became obedient to the magnet 

 when brought near it. 



On Nov. 13, M. Lehot stated to the Academy of Sciences that, 

 notwithstanding the results obtained by M. Fresnel, he was still 

 convinced of the decomposing power given to iron wires by 

 magnets, and quotes experiments he had made six years before 

 by connecting iron wires to the poles of a magnet, and then 

 immersing their ends in water. The south pole caused oxidation, 

 the north pole preserved its wire bright ; again in tincture of 

 litmus ; the south pole reddened the tincture ; the north pole 

 did not. There does not seem any reason to consider these ex- 

 periments as decisive ; and M. Lehot himself does not attach more 

 importance to them than to those made 20 years ago by Ritter, 

 and on the uncertainty of which M. Fresnel had sufficiently 

 remarked. 



On Nov. 13, also, M. Ampere read a note on the electroche- 

 mical effects of a spiral wire subjected to the action of the earth 

 alone. The wire formed a heiix round a paper cylinder, the 

 axis of which was placed parallel to the dip and direction of the 

 needle, the extremities were placed in a solution of common salt. 

 In seven days gas appeared on both ends, but most on that 

 .answering to the negative end of the battery ; the bubbles were 

 displaced, but fresh ones appeared ; the end remaining bright, 

 •while the other end became oxidized, and gave no more gas. 

 On the whole, however, the experiment seemed uncertain, espe- 

 cially after what M. Fresnel had said ; and M. Ampere himself 

 said, that he still doubted as to the existence of the action. 



On Nov. 16, a letter was read at the Royal Society from Sir 

 H. Davy to Dr. Wollaston on the magnetic phenomena produced 

 by electricity. The experiments detailed in it were most of them 

 made in the month of October, and are of very high interest. 

 The peculiar manner in which that philosopher compresses 

 important and numerous facts into few words will seldom permit 

 a condensed account being given of his papers. In the present 

 case, however, there is no occasion to attempt such an account, 

 since the paper itself has appeared in a late number of your 

 Annals, and is to be found at p. 81 of this volume, where the 



9. 



