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an old manuscript with a black ink drawing of a man ' s face on it
Ader

151 - Anne-Robert-Jacques TURGOT (1727–1781).
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Estimate €600 - €800
Sale commission
Description
Anne-Robert-Jacques TURGOT (1727–1781). L.S., Paris, 2 April 1769, to Pierre Cornuau, engineer-geographer for the Map of France at Tulle; two and a half pages, small quarto. A long letter to a colleague of Cassini working on the Map of France concerning the Limousin region. He has received his observations ‘on the plan of operations relating to the land registry which you have trialled in the parish of Soubrevas’. There is indeed a major drawback ‘in the small size of the sheets of paper compared to the scale’; the size of the paper is determined by the size of the planchette, and cannot easily be increased; as for the scale, if it were ‘less than one line to ten feet, I imagine that the new instrument you have devised to make the use of the drawing board both swifter and more precise will provide the means to produce an equally accurate plan on a smaller scale’, but he fears that the measurements may be given with less precision; if the scale is enlarged, this may be a source of error, ‘since it is obvious that the smaller the scale, the easier it will be to misplace the compass points. […] In any event, and even if we were to confine ourselves to surveying at a scale of one line to ten feet, your instrument seems to me to be very useful; consequently, I am determined to have it made, and I would ask you to send me a cardboard model in which the arrangement of your alidades [sighting rules] is clearly shown. It seems to me that you have placed one at each corner; however, I do not see that this is necessary, and at first glance I would think that a sighting rod placed on the movable ruler AB would suffice, given that the diameter DE of the semicircle can be aligned with a visual radius that has already been drawn’… Once his instrument is complete, Turgot will be very keen to verify ‘whether it is possible to achieve the same precision by starting with a plan on a scale of one to three, then converting it to a scale of one line to ten feet, and then taking the measurements from the paper’, and we shall then see which is the best method. Turgot had an idea for easily transferring the plan from one scale to the other: ‘to have a three-pointed reduction compass made, by means of which one could transfer the triangles in their entirety from one plan to the other in a single operation’, which would be impossible with a two-pointed compass…
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About the sale Letters and Autograph Manuscripts – Part I
Auction location
Auction time 10/13/2026 at 2:00 PM
Pictures credits: Contact the Auction House
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