Thomas Jefferson Papers

Thomas Jefferson to Robert Patterson, 10 November 1811

To Robert Patterson

Monticello Nov. 10. 1811.

Dear Sir

I write this letter separate, because you may perhaps think something in the other of the same date, worth communicating to the Committee.

I accept willingly mr Voigt’s offer to make me a timepeice, & with the kind of pendulum he proposes. I wish it to be as good as hands can make it, in every thing useful; but no unnecessary labour to be spent on mere ornament. a plain, but neat mahogany case will be preferred.

I have a curiosity to try the length of the pendulum vibrating seconds here: and would wish mr Voigt to prepare one which could be substituted for that of the clock occasionally, without requiring any thing more than unhanging the one and hanging the other, in it’s place. the bob should be spherical, of lead, and it’s radius, I presume, about one inch. as I should not have the convenience of a room of uniform temperature, the suspending rod should be such as not to be affected by heat or cold, nor yet so heavy as to affect too1 sensibly the center of oscillation. would not a rod of wood, not larger than a large wire, answer this double view? I remember mr Rittenhouse told me he had made experiments, on some occasion on the expansibility of wood lengthwise by heat, which satisfied him it was as good as the gridiron for a suspender of the bob. by the experiments on the strength of wood & iron in supporting weights appended to them, iron has been found but about six times as strong as wood, while it’s specific gravity is eight times as great. consequently a rod of it, of equal strength, will weigh but ¾ of one of iron, and disturb the center of oscillation less in proportion. a rod of wood of white oak e.g.2 not larger than a seine twine would probably support a spherical bob of lead of 1.I. radius. it might be worked down to that size, I suppose, by the cabinet makers, who are in the practice of preparing smaller threads of wood for inlaying. the difficulty would be in making it fast to the bob at one end, and scapement at the other, so as to regulate the length with ease & accuracy. this mr Voigt’s ingenuity can supply, and in all things I would3 submit the whole matter to your direction to him, and be thankful to you to give it.

Your’s affectionately

Th: Jefferson

PoC (DLC); at foot of text: “Doct: Robert Patterson.” SJL records only one 10 Nov. 1811 letter to Patterson.

1Word interlined.

2Preceding four words interlined.

3TJ here canceled “wish.”

Index Entries

  • building materials; mahogany search
  • building materials; oak search
  • clocks; TJ’s astronomical case clock search
  • Patterson, Robert; and astronomical case clock search
  • Patterson, Robert; letters to search
  • pendulum; in clocks search
  • Rittenhouse, David; and astronomical case clock search
  • Voigt, Thomas; and TJ’s astronomical case clock search