To David Rittenhouse
New York June 14. [i.e. 15] 1790.
I inclosed you, the day before yesterday a rough draught of the report I had prepared on the subject of weights and measures. I have this morning recieved from Mr. Short a proposition made by the Bishop of Autun to the National assembly of France on the same subject, which I inclose you, and will beg the favor of you to return it by post after you shall have perused it. He mentions that the lat. of 45.° as being a middle term between the Equator and pole had been proposed as the general standard for measures, and he makes the proposition anew, and desires it should be made to England. As this degree of Latitude is our Northern boundary, as it may form a link between us and Europe, and as the degree which shall give the standard is not otherwise very material, I have thought of proposing it in my report instead of the 38th. degree. I have in consequence gone over my calculations again upon the ground of a pendulum of 36 pouces 8,628 lignes (Sr. Isaac Newton’s calculation for 45°) 39. inches giving a rod of 58.72368 inches, and reformed the tables (last page of the report) of which reformation I send you a copy. The alterations in the body of the work may be easily made from this. The bishop sais the pendulum has been calculated for 45.° to be 36. pouces 8.52 lignes. This is 1/10 of a line less than Sr. I. Newton’s, and the Bishop accordingly adds that there may be in this calculation an error of 1/10 of a line.
I had taken no notice of the precaution of making the experiment of the pendulum on the sea-shore, because the highest mountain in the U.S. would not add 1/1000 part to the length of the earth’s radius, nor 1/128 of an inch to the length of the pendulum: the highest part of the Andes indeed might add about 1/1000 to the Earth’s radius, and 1/25 of an inch to the pendulum. As it has been thought worth mention, I will insert it also.
Your letter of Apr. 20. was duly attended to by me, but I fancy the successor had been decided on before it was known to the public that there would be a vacancy. I am with great esteem, my dear Sir, Your sincere friend & humble servt.,
PrC (DLC); proof of the error in date exists in the entry in SJL for 15 June 1790 recording receipt of Short’s letter of 29 Mch. 1790, and also in Hamilton’s acknowledgement on Wednesday, 16 June 1790, of a (missing) “note of yesterday” which clearly had transmitted to him the same information that TJ here presented to Rittenhouse.