Papers on Magnetism

This grouping details Cavendish's observations of declination (the angle between magnetic north and true north) and magnetic dip (the angle made with the horizontal by the Earth's magnetic field lines, or vertical inclination). Magnetic declination varies over time, hence Cavendish conducting measurements over the course of decades. Cavendish was also concerned with the accuracy of the instruments used to measure magnetic declination and dip, leading to trials of various "needles" and experiments with substances that may cause deflection. Cavendish worked with his father Lord Charles Cavendish, using his instruments to make observations in the garden of his house at Great Marlborough Street.

The grouping may be the "small packet marked "Cavendish Papers" which had been sent to the Meteorological Office by Sir Edward Sabine" that James Clerk Maxwell was sent by Robert H. Scott FRS (see Maxwell, James Clerk "The Electrical Researches of the Honourable Henry Cavendish F.R.S." (1879; Cambridge, Cambridge University Press), plxiv). It is unclear how they came into the possession of Sabine. All this material was examined by Dr Charles Chree F.R.S., Superintendent of the Kew Observatory, as related in Thorpe, Sir Edward "The Scientific Papers of Henry Cavendish" (1921; Cambridge, Cambridge University Press) Vol II, pp438-92, which includes a useful summary of the records' contents at pp438-42 from which much of the description for this grouping of records is based. The records mentioned between p438-442 follow the same order as HY/9/1-44.

HY/9/1-44 was arranged prior to 2024. In 2024, HY/9/45 added from a folder marked "Misc (Astron)"; HY/9/46 was added from a folder marked "Misc (unclassified)"; HY/9/47 was added from a folder marked "Two papers on magnetic needles"; and HY/9/48 was added from a folder marked "experiments on magnets MS". This re-arrangement was made on the basis of subject matter.