To David Rittenhouse
New York June 30. 1790
Your favor of the 25th. came to hand last night, for which I give you many thanks. The conversion of 36.71428 pouce[s] into 39.1923 inches was an error in division, and consequently the mean taken between that and Graham’s computation is wrong. It has rendered it necessary for me to suppress the note on that subject, and to put it into the form now inclosed. In this I state the reaso[n] for adopting 11 po. 3.li. as the equivalent of the English foot. It is so stated by D’Alembert in the Encyclopedie, and retained in the new Encyclopedie. To have changed it for 11-3.11, Maskelyne’s measure, would have obliged me to reform all my calculations anew which would have [expos]ed me to new errors of calculation, and added to the trouble and delay it wo[uld] have occasioned, did not seem worth while for so small a fraction as 11/100 of a line or the 1227th. of a foot. I suppose too that the operation concerti[ng] between the French and English will soon furnish us with a new and mor[e] perfect equation of their feet. I still like the rod rather than the pendulum because I do not know a single objection to it which does not [lie] against the pendulum, because it is clear of some objections to which that is liable, but most of all because ⅕ of the second rod is much nearer the present foot than ⅓ of the second pendulum. After all, should the French and English adopt the pendulum, we shall be free to do so also.—I state on the inclosed paper the very loose answer to the 5th. objection, which is the only one I am enabled to give. Can you suggest something more precise? As there is an [id]ea that Congress will rise about the middle of July, I shall only await the answer you will be so good as to make to this and then give in the report.—This day, I fancy, will determine whether we are to be removed to Philadelphia or not. For tho’ it will still be to be put to the question several times before it’s ultimate passage, yet I think, if this day’s vote of the Senate is favorable, it will pass safely thro’ all the [su]bsequent stages. It would have been a great comfort to [me] to have been near you during the preparation of this [bu]siness of weights and measures. It is much easier to avoid [e]rrors by having good information at first, than to unravel and correct them after they are committed. I recommend to Congress the deferring to proceed on the report till the next session, and reserve to myself an opening to add any new matter which may occur in the mean time.—I am with great & sincere esteem Dr. Sir Your affectionate friend & servt.,
P.S. The Senate have past the vote in favor of the residence at Philadelphia till the 1st. of January 1800. I believe now there will be no more changes. 2. oclock P.M.
RC (Miss Elizabeth Sergeant Abbot, Philadelphia, 1954); margin of MS torn, parts affected supplied from PrC; addressed: “David Rittenhouse esquire Philadelphia” franking signature cut out; postmarked: “[NEW-YOR]K * june 30” and “FREE.” PrC (DLC); lacks postscript, which was added on 1 July 1790 shortly after TJ received from Samuel A. Otis a note of that date reading: “Mr. Otis’s respects to the Secretary of State and informs him the Bill has passed the Senate” (RC in DLC; not endorsed and not recorded in SJL—but covered with calculations by TJ for his report on weights and measures; see under 4 July 1790 for that report and Document vii, note 15, for the 5th objection.)