SIR,--I have to acknowledge the receipt of your favor of December 20th, and am much pleased to find our progress in manufactures to be so great. That of cotton is peculiarly interesting, because we raise the raw material in such abundance, and because it may, to a great degree, supply our deficiencies both in wool and linen. A former application on behalf of Messrs. Binney & Robertson, was delivered to the Secretary of State, who will engage General Armstrong to aid such measures as they may take in Paris for obtaining permission to draw supplies of Antimony from thence. It will give me real pleasure to see some good system of measures and weights introduced and combined with the decimal arithmetic. It is a great and difficult question whether to venture only on a half reformation, which by presenting fewer innovations, may be more easily adopted, or, as the French have tried with success, make a radical reform. Your plan presents as few innovations as any I have seen; but I think your _foot_ should refer to the pendulum, by saying, for instance, that the _foot_ shall be a measure which shall be to the second pendulum as 1 to 3,267; or rather as 1 to the length of a pendulum vibrating seconds in latitude 45°. This offers a standard in every place, because it can everywhere be found. The rod you propose is only to be found in Philadelphia. You say in your letter that "if the decimal mode obtain in the division of the pound, the Troy and it, as regards the Troy grain, would be the same." I do not understand this; because the Avoirdupois pound containing 7,000 Troy grains, I do not see how any decimal subdivision of the pound could coincide with the Troy grain. However, I shall be very glad to see adopted whatever measure is most promising. I salute you with esteem and respect. TO THE REV. MR. MILLAR. WASHINGTON, January 23, 1808.