"The length of the pendulum has been differently estimated by different persons. Knowing no reason to respect any of them more than Sir Isaac Newton for skill, care, or candor, I had adopted his estimate of 39.149 I. for our northern limit of 45°, before I saw the different propositions of the Bishop of Autun, and Sir John Riggs Miller. The first of these gentlemen quotes Mairan's calculation for 48° 50', the latitude of Paris, to wit, 504:257::72: to a 4th proportional, which will be 36.71428=39.1923 inches. The difference between the pendulum for 48° 50' and 45°, as calculated by Sir I. Newton, is .0112 I. so that the pendulum for 45° would be estimated, according to the Bishop of Autun, at 39.1923-.0112=39.1811. Sir John Riggs Miller proposes 39.126, being Graham's determination for 51° 31', the latitude of London. The difference between the pendulum for 51° 31', and 45° by Sir I. Newton, is .019 I., so that the pendulum for 45° should be estimated according to Sir J. R. Miller, at 39.126-.019=39.107 I. Now, dividing our respect between these two results, by taking their mean, to wit, (39.181 + 39.107)/2=39.144, we find ourselves almost exactly with Sir I. Newton, whose estimate of 39.149 we had already adopted." I propose also to reform a passage under the head of Weights, in the first branch of the report, to stand thus: "Let it then be established, that an ounce is the weight of a cube of rain water of one-tenth of a foot, _or rather, that it is the thousandth part of the weight of a cubic foot of rain water_ weighed in the standard temperature," &c. All which I submit to your judgment, and I will ask you particularly to examine the numbers .0112 and .019, as I have no help here to find them otherwise than by approximation. I have wished much, but in vain, Emerson's and Ferguson's books here. In short, I never was cut off from the resources of my own books and papers at so unlucky a moment. There is a Count Andriani, of Milan, here, who says there is a work on the subject of weights and measures published by Trisi of Milan. Perhaps you may have it at Philadelphia, and be able to send it to me. Were it not for my confidence in your assistance, I should not have ventured to take up this business till I received my books. I am, my dear Sir, with great and sincere esteem, your friend and servant. TO JAMES MONROE. New York, June 20, 1790. Dear Sir,--An attack of a periodical headache, which, though violent for a few days only, yet kept me long in a lingering state, has hitherto prevented my sooner acknowledging the receipt of your favor of May 26. I hope the uneasiness of Mrs. Monroe and yourself has been removed by the re-establishment of your daughter. We have been in hopes of seeing her here, and fear at length some change in her arrangements for that purpose.