Thomas Jefferson Papers

From Thomas Jefferson to Joseph Coolidge, May 1825

A clock is wanting for the Rotunda of the University; the size and strength of it’s works must be accomodated to two data.

1. the bell weighs 400. ℔ and is to be heard . with certainty 1½ miles

2. the dial-plate is to be about 6. feet 3. I. diameter. it is to be fixed in the tympanum of the Pediment of the Portico. The triangle of this tympanum has not been measured exactly yet, therefore we cannot exactly ascertain the size of the dial plate it will admit.

the bell is to remain free to be rung.

the ropes for the weights will have to go directly back about 30 f then turn off at a right angle horizontally about 21. f. to the hole of their descent, which is 50. feet deep consequently upwards of 100 f. long

the rope for springing must do the same, but on the opposite side, where there are stairs.

it must be wound up on the back or inside.

and the hands must be set right by a key on the back or inside

what will such a clock cost?

+ 9
the tympanum is  9–4  in the perpendicular } measured within the cornice.
42. f.  in the span
the hole for the descent of the weights is  5. f. diam. in the clear opening
48  f. depth, i.e from the level of he axis of the dial plate to the ground

Within the naked of the form? the tympanum, a circle of 52. I. rad, may be insubl but more than this may I believe be obtained if necessary for the pendulum, the whole interior of the roof of the Portico being vacant.

allowing the dial plate 5. f. diam. clear within the tympanum, embedded in an architrave of 10. I. breadth, there will still be a space or margin 12. I. wide in it’s narrowest parts.

the dial plate must be of metal of course, as wood would soon rot. in addition therefore to the 5. foot of dial plate which will shew there must be margin to be imbedded in a rabbet of sfft breadth to hold it firm within the architrave.


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