We were much disappointed in Virginia generally on the day of the great eclipse [June 24, 1778], which proved to be cloudy. In Williamsburgh, where it was total, I understand only the beginning was seen. At this place which is in Lat. 38° 8′ and Longitude West from Williamsburgh about 1° 45′ as is conjectured, eleven digits only were supposed to be covered. It was not seen at all till the moon had advanced nearly one third over the sun’s disc. Afterwards it was seen at intervals through the whole. The egress particularly was visible. It proved however of little use to me for want of a time peice that could be depended on;
To David Rittenhouse, July 19, 1778
Patrick Lee’s Explanation
On this day when the solar eclipse crosses the United States, this is young Jefferson’s (age 35) comment on the 1778 eclipse, which darkened the southeastern portion of the country three weeks before. Monticello was north of the zone of totality, perhaps in the 90% range. The presence of clouds and the absence of a reliable clock thwarted his ability to make scientific observations.
Rittenhouse (1732-1796) was a famed American astronomer, mathematician and clockmaker. Two of his many accomplishments were recording the transit of Venus across the face of the sun in 1769 and the creation of an orrery, a mechanical representation of our solar system.
Jefferson reminded his friend of his offer to make for him “an accurate clock,” essential for astronomers, and asked when that clock might arrive.