| Description | Graph showing variations in the Earth's magnetic field at Washington D.C., measured over two days at half hourly intervals. Below the graph are twelve barometer readings taken over the course of the observations, and temperature readings [in Fahrenheit] by thermometer 'in Magntc. Obsty.'.
Headed: 'Variation of the Magnetic Needle as observed at Washington City D.C. from 3h 30' July 24th to 3hr 00' 25th inclusive. Gottingen Mean Time.'. The date of '1840' has been added, together with 'No. 345 Recd. 9th August 1842', and the authorship notation 'By Lieut. Gillies of the United States Service. Communicated by S. Hunter Christie Esqre. Sec. R.S.'.
Endorsed verso: 'No. 345 Meteorological Archives 4 May 1843 S.H.C.' and '35 Washington City, D.C. Magnetical Observations July 1840.' With a note: 'To be sent to the Royal Society'. |