And why should not our society open the proposition by a circular letter to the other learned institutions of the earth? If men of science, in their publications, would express measures always in multiples and decimals of the pendulum, annexing their value in municipal measures as botanists add the popular to the botanical names of plants, they would soon become familiar to all men of instruction, and prepare the way for legal adoptions. At any rate, it would render the writers of every nation intelligible to the readers of every other, when expressing the measures of things. The French, I believe, have given up their Decada Calendar, but it does not appear that they retire from the centesimal division of the quadrant. On the contrary, M. Borda has calculated according to that division, new trigonometrical tables not yet, I believe, printed. In the excellent tables of Callet, lately published by Didot, in stereotype, he has given a table of Logarithmic lines and tangents for the hundred degrees of the quadrant, abridged from Borda's manuscript. But he has given others for the sexagesimal division, which being for every 10´´ through the whole table, are more convenient than Hutton's, Scherwin's, or any of their predecessors. It cannot be denied that the centesimal division would facilitate our arithmetic, and that it might have been preferable had it been originally adopted, as a numeration by eighths would have been more convenient than by tens. But the advantages would not now compensate the embarrassments of a change. I extremely regret the not being provided with a time-piece equal to the observations of the approaching eclipse of the sun. Can you tell me what would be the cost in Philadelphia of a clock, the time-keeping part of which should be perfect? And what the difference of cost between a wooden and gridiron pendulum? To be of course without a striking apparatus, as it would be wanted for astronomical purposes only. Accept assurances of affectionate esteem and respect. TO CLEMENT CAINE, ESQ. MONTICELLO, September 16, 1811.