Thomas Jefferson Papers

To Thomas Jefferson from Robert Leslie, 1 July 1790

From Robert Leslie

Philadelphia July 1st 1790


I was this day honourd with your favour of the 27th ult, in which you are pleased to express your satisfaction with respect to the vibrating rod, which I proposed as a standard of measure. I shall think myself still further honourd, and you have my hearty consent, that you report the same to Congress as the standard of measure for the U.S. I would just further beg leave to observe that since writing the piece you refer to I have been informed by Mr. Patterson Professor of Mathematics in the University here, to whome I mentioned the project, that in the vibrating rod, the center of oscillation is not strictly and Mathematically at ⅔ of the lenght of the rod from the end or point of suspension, that this is the case only on the supposition of the rod being a mere inflexible line. He however assures me, upon making the calculation that the error in any rod which would be used for this purpose would be totally insensible. A rod for instance of 40 inches long and 4 tenths of an inch in diameter would have the distance of its center of oscillation below ⅔ of the lenght of the rod only 1/2000 part of an inch, or 1/80000 part of the whole lenght, a fraction scarcely within the power of a micrometer to measure, and may therefore be safely neglected. Any assistance which it may be in my power to render respecting the above scheme, or any other in which you may be pleased to employ me, you may be assured will be always at your Service. I have the honour to be Sir your most obedt. humble servt.,

Robert Leslie

A rod of 40 inches long and 2 tenths of an inch in diameter will have its center of oscilation below ⅔ of the lenght of the rod { 1/3000*
One of 4 tenths diameter { 1/2000
one of 8 tenths diameter { 1/1500

* This perhaps will be the variation of the rod which will be most convenient which is only 1/3000 part of an inch.

RC (ViWC); endorsed as received 3 July 1790 and so recorded in SJL The postscript (also ViWC) is on a separate piece of paper, and is separated from the letter, but obviously was integral with it originally.

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