| RefNo | MS/242/2 |
| Level | Item |
| Title | Letter from Jean François Dominique Arago to Thomas Young, dated at the Observatoire Royal, Paris |
| Date | 9 March 1818 |
| Description | Letter addressed to Young, as Secretary of the Royal Society.
Arago has recently recovered from a serious illness which kept him in bed for three weeks. Before letting Young know of the best method to determine changes in intensity of the magnetic force, Arago has looked carefully at various magnetic observations from across the world. He concludes that there is only one method exact enough to appreciate the variations of the magnetic force from the Equator to the pole, which consists in counting the oscillations of the same horizontal needle, suspended inside a glass cage by a silk thread. The oscillations of a vertical needle would slow down too quickly under the influence of the spindle, Arago has deduced this from the unreliable observations taken following this method even by the most practised of observers. Whatever the method, the measure needs to be taken from a stable location, so one must be thankful that sailors have to disembark regularly.
The packet of needles previously sent by Young was delivered to [George] Cuvier. Arago had delivered the packet for Mr LeRoy at his former address but he hopes it has reached him.
All in Paris are looking forward to hearing of Young's method with the pendulum. In a few days Arago will communicate their own conclusions on the invariable pendulum along with the hieroglyphic drawings. Egyptologist [Edmé-François] Jomard, whose wife has just given birth, has been out of circulation for a few days.
Sends regards from Mrs [Lucie Carrier-Besombes] Arago, send his compliments to Mrs [Eliza Maxwell] Young, Mr [Henry] and Mrs [Mary Frances Reeve] Kater, Dr [William Hyde] Wollaston.
In post-scriptum notes that he has handed to Mr [Jean-Baptiste] Huzard Junior the latest number of the Connaissance de la Terre for Young and hopes he has received it. |
| Language | French |
| Extent | 4p |
| Format | Manuscript |
| PhysicalDescription | Paper |
| AccessStatus | Open |
Fellows associated with this archive
| Code | PersonName | Dates |
| NA7947 | Young; Thomas (1773 - 1829); physician, physicist and Egyptologist | 1773 - 1829 |
| NA2974 | Arago; Dominique Francois Jean (1786 - 1853); mathematician, physicist, astronomer and politician | 1786 - 1853 |