 |
| Explore this site |
|
 |
|
| © National Maritime Museum, London |
| |
| Repro ID: D3355 |
| Description: A portable transit instrument similar to that used on James Cook’s Transit of Venus expedition of 1769. This telescope is made by Jesse Ramsden with optics by John Dollond and inscribed ‘Fait par Ramsden pour Dollond, London’. It is a 3.5-ft (106 cm) transit instrument with a focal length of 42 inches (106 cm), an aperture of 1.75 inches (4.45 cm) and axis of 30 inches (76 cm). A similar 4-ft (122 cm) transit instrument by John Bird, belonging to the Royal Society, was taken in the 'Resolution' on Cook’s second voyage and in the 'Discovery' on the third voyage. One of the important objects of these two voyages was the testing of the newly invented marine chronometers. This could be done better by transit instrument than by astronomical quadrant, though setting up and adjusting the former was a tedious business, requiring much digging to get firm foundations. The transit instrument shown here was probably made a few years after Bird’s, but it would have been very similar in appearance and performance to the one that accompanied Cook, which does not seem to have survived. |
| Creator: Jesse Ramsden |
| Date: c. 1780 |
| Credit line: National Maritime Museum, London | |
|
|
|
|
