On certain irregularities in the magnetic needle, produced by partial warmth, and the relations which appear to subsist between terrestrial magnetism and the geological structure and thermo-electrical currents of the earth

• Published in: Abstracts of the Papers Printed in the Philosophical Transactions of the Royal Society of London
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 1837
• Subjects: North Pole; The Needle
• Online Access: http://dx.doi.org/10.1098/rspl.1830.0066; https://royalsocietypublishing.org/doi/pdf/10.1098/rspl.1830.0066

The author begins by an account of some experiments which he instituted with a view to discover the cause of the irregularities in the indications of the intensity of terrestrial magnetism given by the vibrating magnetic needle. By inclosing the needle in a box surrounded with water at different temperatures, the number of the vibrations did not appear to be affected by these differences of temperature when the heat was applied equally on all sides j but when partially applied, irregular oscillations took place, apparently from the currents of air set in motion by the inequalities of its temperature. Hence the author recommends that for delicate experiments the magnetic needle should be contained in a box of wood, or other imperfect conductor of h eat; or, for still greater security, that it should be adjusted in a glass vessel exhausted of air. For experiments on magnetic intensity at sea, he recommends placing two magnets at some distance from the needle, in the line of its magnetic meridian, and surrounded with water, in order to preserve a uniformity of temperature. For increasing the action of terrestrial magnetism, he suggests the employment of a bar or cylinder of wrought iron, placed perpendicularly, or in the line of the dip, at right angles to the meridian, so as to repel the north pole of the needle: and also surrounded with water. The experiments made with an apparatus of this kind in some of the deep mines in Conwall, did not lead to the conclusion that there is any increase of magnetic intensity at the depth of 1000 or 1200 feet below the level of the sea; but if any thing, rather the reverse; but, on the whole, the discrepancy in the results was so great, that no dependence can be placed on them as establishing a general fact of this importance.