| RefNo | MS/242/27 |
| Level | Item |
| Title | Letter from Augustin Jean Fresnel to Thomas Young, dated at Paris |
| Date | 16 September 1823 |
| Description | Addressed to Young as Secretary of the Royal Society.
Hasn't been able to conduct much research in optics, as has been busy with lighting of lighthouses. Has spent the whole month of July in the Cordouan lightouse in Gironde installing a dioptric lens [now known as a Fresnel lens]. The lens which has been operational since 25 July 1823 is so bright it took English tourists and English sailors by surprise. Hopes to gather some testimonies on the usefulness of the lens from experienced sailors over the coming months, if Young hears anything on the topic, asks to send the observations over. The lens provides both a landmark out at sea and a fine light for sailors getting into the estuary, visible from 4 nautical miles and visible constantly close to submerged obstacles. The additional close range light is provided without any additional fire to save in expense of oil, reflecting the light from under the rotating lense using small mirrors. Very efficient oil consumption of 1,5 pounds per hour, while the previous lens used 3 pounds per hour, which means a saving of over 6,000 francs per year as well as improved light. |
| Language | French |
| Extent | 3p |
| 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 |
| NA7031 | Fresnel; Augustin Jean (1788 - 1827) | 1788 - 1827 |