Sir Humphry Davy on the 
iS 
across, or circular pieces of steel fitted for making horse-shoe 
magnets, round the electrical conductors of buildings in ele- 
vated and exposed situations.* 
The experiments detailed in these pages were made with 
the apparatus belonging to the Royal and London Institu- 
tion ; and I was assisted in many of them by Mr. Pepys, 
Mr. Allen, and Mr. Stodart, and in all of them by Mr. 
FARADAY.-f 
lam, my dear Sir, 
very sincerely yours, 
Humphry Davy, 
Lower Grosvenor Street , 
Nov. 12, i 82 o. 
* 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 box of knives, rendered most of them powerful magnets. See Phi- 
losophical’Transactions, No. 157, p. 520; and No. 437, p. 57. 
f All the experiments detailed in this paper, except those mentioned p. 15, were 
made in the course of October, 1820 ; the last arose in consequence of a conversation 
with Dr. Wollaston, and were made in the beginning of November. I find, by 
the Annales de Chimie et de Physique, for September, which arrived in London 
November 24, that M. Araco has anticipated me in the discovery of the attractive 
and magnetizing powers of the wires in the voltaic circuit ; but the phenomena pre- 
sented 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. Araco likewise 
thought of, — whether the arc of flame of the voltaic battery would be affected by 
the magnet ; but from the imperfection of our apparatus, the results were not deci- 
sive. 1 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 phe- 
nomena, I have passed the electrical shock along a spiral wire twisted round a glass 
