Letter, regarding the survey of the East Indian Archipelago from Charles Morgan Elliot to Colonel [Edward] Sabine Elliot describes the process of taking magnetic observations, listing the locations where he undertook the observations and the equipment used in the process. Subject: Hydrology / Meteorology Written by Elliot in Madras [Chennai, India]. 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 'A Letter from Captain C. M. Elliot, Madras Engineers, to Lieut.-Col. Sabine, For. Sec. R.S., transmitted through the Court of Directors of the East India Company. Communicated by Lieut.- Col. Sabine.' 6 August 1849