TO DAVID RITTENHOUSE.
New York, June 14, 1790.
Dear Sir,—I enclosed 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 received from Mr. Short a proposition made by the Bishop of Autun to the National Assembly of France, on the same subject, which I enclose you, and will beg the favor of you to return it by post after you shall have perused it. He mentions that the latitude 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 may 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 otherwise 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.-8.428. (Sir Isaac Newton's calculation for 45°) 39.14912 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 says the pendulum has been calculated for 45° to be 36.-8.52. this 1-10 of a line less than Sir Isaac 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 United States would not add 1-5000 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 April 20th, 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 and humble servant.