Letter, 'Remarks on de la Rive's theory for the physical explanation of the causes which produce the diurnal variation of the magnetic declination' from Edward Sabine to Samuel Hunter Christie Sabine writes of a theory regarding 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 [South Africa]. Annotations in ink throughout. Subject: Magnetism / Meteorology Received 19 April 1849. Communicated by Christie. Written by Sabine in Woolwich [London]. This letter was published in full in volume 5 of Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London [later Proceedings of the Royal Society] as 'Remarks on M. De la Rive’s theory for the physical explanation of the causes which produce the diurnal variation of the magnetic declination. In a letter to S. Hunter Christie, Esq., Sec. R. S., from Lieut.-Col. Sabine, For. Sec. R. S. Communicated by S. Hunter Christie, Esq'. 16 April 1849