Directions for Building the Great Clock, [1792–1793]
Directions for Building the Great Clock
[1792–1793]
- The works are 15 I. deep, from the plate to the farthest point in the back.1 A circle of 12 I. radius round the center of the hour circle, will barely cover the remotest point of the works.
- The center of vibration of the pendulum is 7. I. above the2 back end of the axis of the hour hand.
- The arc of vibration is (at the bob3) 18. I.
- The same arc, at 7. I. below the center, will be 3. I.
- Then a toothed wheel of 2.4 I. on the back-end of the5 axis of the hour hand, taking in an equal wheel whose axis will be of course 26 I. horizontally from that of hour hand, will be clear of the vibration of the pendulum, and may turn an hour hand on the reverse face of the wall on a wooden hour plate of 12. I. radius. There need be no minute7 hand, as the hour figures will be 6. I. apart. But the interspace should be divided into quarters and 5. minute marks. The fore and back hour-plates will not be concentric.8
- The9 axis of the second hand 4 ⅙ I. from that of the hour-hand (i.e. their centers)
- The radius of the second circle (i.e. length of hand) 1¾ I.
MS (DLC: TJ Papers, 233: 41588); written entirely in TJ’s hand on a small sheet; undated.
The Great Clock: a large, seven-day timepiece gracing the entrance to Monticello, with faces hanging inside the Entrance Hall and outside beneath the East Portico, that with occasional restoration has continued to operate to the present day (see illustration). TJ certainly penned these instructions for the clock before 27 Apr. 1793, when he paid $113.80 for the instrument to the Philadelphia clockmaker Robert Leslie, whose employee Peter Spurck had constructed it, and probably before 13 Nov. 1792, when he asked Henry Remsen to help obtain a gong for the device (, 27 Apr. 1793, and note; TJ to Remsen, 13 Nov. 1792). For the fullest treatment of the clock’s construction, installation, and operation, see Silvio A. Bedini, “Thomas Jefferson, Clock Designer,” , Proceedings, cviii (1964), 165–70; for the clock as pictured in its architectural setting, see William H. Adams, Jefferson’s Monticello (New York, 1983), 109, 110, 118–19, 196. See also , 376–7.
1. Sentence interlined.
2. TJ here canceled “point.”
3. Word interlined in place of “uttermost.”
4. Digit written over “3.”
5. Preceding three words interlined.
6. Digit interlined in place of “4.”
7. Word interlined in place of “second.”
8. Sentence interlined.
9. TJ here canceled “center.”