My dear Sir,
The Annales de Chimie et de Physique
for March last contains a letter from M. De la Rive to M. Arago, in which a theory is proposed, professing to explain on physical principles the general phenomena of the diurnal variation of the magnetic declination, and, in particular, the phenomena observed at St. Helena and at the Cape of Good Hope, described in a paper communicated by me to the Royal Society in 1847, and which has been honoured with a place in the Philosophical Transactions. Although I doubt not that the inadequacy of the theory proposed by M. De la Rive for the solution of this interesting problem will be at once recognised by those who have carefully studied the facts which have become known to us by means of the exact methods of investigation adopted in the magnetic observatories of recent establishment, yet there is danger that the names of De la Rive and Arago, held in high and deserved estimation as authorities on such subjects, attached to a theory, which moreover claims reception on the ground of its accordance with “well-ascertained facts” and “with principles of physics positively established,” may operate prejudicially in checking the inquiries which may be in progress in other quarters into the causes which really occasion the phenomena in question; I have thought it desirable therefore to point out, in a very brief communication, some of the important particulars in which M. De la Rive’s theory fails to represent correctly the facts which it professes to explain, and others which appear to me to be altogether at variance with, and opposed to it.
LXXXVI. Observations for proving the going of Mr. Ellicott's clock, at St. Helena
