88 On Magnetic Phenomena produced by Electricity. [Aug. 



course of the sun, the magnetism of the earth ought to be such 

 as it is found to be. 



But I will quit conjectures, to point out a simple mode of 

 making powerful magnets, namely, by fixing bars of steel across, 

 or circular pieces of steel fitted for making horse-shoe magnets, 

 round the electrical conductors of buildings in elevated and 

 exposed situations.* 



The experiments detailed in these pages were made with the 

 apparatus belonging to the Royal and London Institution ; and 

 I was assisted in many of them by Mr. Pepys, Mr. Allen, and 

 Mr. Stodart, and in all of them by Mr. Faraday .-\ 



I am, my dear Sir, very sincerely yours, 



Lou'cr Grosvenor-slreet, A r ov. 12, 1820. Hu MPHRY DAVY. 



* There are many facts recorded in the Philosophical Transactions which prove the 

 magnetizing powers of lightning ; one in particular, where a stroke of lightning passing 

 through a hox of knives, rendered most of them powerful magnets.— (See Phil. Trans. 

 No. 157, p. 520; and No. 437, p. 57.) 



-f- All the experiments detailed in this paper, except those mentioned p. 86, were 

 made in the course of October, 1820; the last arose in consequence of a conversation 

 with Dr. Arollaston, and were made in the beginning of November. I find, by the 

 Annales de Chimie et de Physitme, for September, which arrived in London Nov. 24, 

 that M. Arago has anticipated me in the discovery of the attractive and magnetizing 

 powers of the wires in the voltaic circuit; but the phenomena presented by the action 

 of common electricity (which I believe as yet have been observed by no other person), 

 induce me still to submit my paper to the Council of the Royal Society. Before any 

 notice arrived of the researches of the French philosophers, I had tried, with Messrs. 

 Allen and Pepys, an experiment, which M. Arago likewise thought of, — whether the 

 arc of flame of the voltaic battery would be affected by the magnet; but from the imper- 

 fection of our apparatus, the results were not decisive. I hope soon to be able to repeat 

 it under new circumstances. 



I have made various experiments, with the hope of affecting electrified wires by the 

 magnetism of the earth, and of producing chemical changes by magnetism ; but without 

 any successful results. 



Since I have perused M. Ampere's elaborate treatise on the electro-magnetic pheno- 

 mena, I have passed the electrical shock along a spiral wire twisted round a glass tube 

 containing a bar of steel, and I found that the bar was rendered powerfully magnetic 

 by the process. 



Without meaning to offer any decided opinion on that gentleman's ingenious views, I 

 shall beg permission to mention two circumstances, which seem to me unfavourable to 

 the idea of the identity of electricity and magnetism ; first, the great distance to which 

 magnetism is communicated by common electricity (I found that a steel bar was made 

 magnetic at 1 4 inches distance from a wire transmitting an electric shock from about 

 70 feet of charged surface) ; and, secondly, that the effect of magnetizing at a distance 

 by electricity takes place with the same readiness through air and water, glass, mica, or 

 metals ; i. e. through conductors and non-conductors. 



