| Title | Unpublished paper, 'A statement of the working of compasses on board the honourable East India Company's iron steamer Pluto, from September 1841, on her passage from England to China, and during her service in those seas, until her arrival at Calcutta [Kolkata, India] in January 1843' by John Tudor |
| Description | Tudor states that the compasses of the Pluto were adjusted by Mr Sims, of the firm of Troughton and Sims, by order of Mr Pencoote of the East India House, under whose directions that ship was fitted out: and it is to the great pains taken by Mr Sims in placing the magnets employed for counteracting the local attraction that the author attributes the undeviating accuracy of those compasses during the whole time the Pluto was under his command in both hemispheres. He observes that, in the first place, much care is required in securing the magnets, and protecting them from water, after their proper position has been ascertained. In the case of the Pluto, two magnets were placed under the deck in the author’s cabin; one of them eighteen inches below the deck. The next point to be attended to is that the cards, or needles, should be all of the same size, and exactly corresponding with that of the compass used at the placing of the magnets for counteracting the local attraction. The bittacles should all be of the same make and height, and the compass-boxes of the same size; so that whenever a new compass or a fresh bittacle is wanted, the circle in which the needle moves may remain at the same angle from the magnet as at the first adjustment. On a strict attention to these precautions will depend the well-working of the compass in all iron vessels, and also in wooden vessels when-ever the quantity of iron they contain creates the necessity of measures being taken for counteracting local attraction. It has been alleged that the adjustments for local attraction made in northern latitudes are not correct when the ship is south of the equator; but the author states that, in the Pluto, he observed no difference that ship having made, while under his command, passages of many thousand miles, comprising 94 degrees of latitude, namely from 51 degrees North to 43 degrees South, and 153 degrees of longitude, namely from 30 degrees West to 123 degrees East, during the whole of which he never found any other correction for the compasses necessary excepting that required for the magnetic variation, the local attraction having been completely neutralized.
Includes one diagram in the text showing the placement of the magnets. Marked on back as 'Archives 4 May 1848 S H C [Samuel Hunter Christie]'.
Subject: Magnetism / Marine engineering
Received 8 February 1848. Communicated by Samuel Hunter Christie.
Whilst the Royal Society declined to publish this paper in full, an abstract of the paper was published 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 statement of the working of the compasses on board the honorable East India company’s iron steamer Pluto, from September 1841, on her passage from England to China, and during her service in those seas, until her arrival at Calcutta in January 1843'. |