London 17. Octobr 1807
I was honored with your’s of last year, Dated Octr 25th. and have used my best endeavours to execute such Instruments for you as I thought would best answer your purpose As you expressed that you wanted the Astronl Quadt for an important purpose, & that Instrument, being on a confined and limited principle of Accuracy I judged it best to send you the Reflecting Circle. This Instrument will enable you to take angular distances in all directions, to the accuracy of *20 seconds or less and whether for the purpose of determining the latitudes & longitudes of places, altitudes or azimuths triganometl angles for Surveys on land, &c, &c, this is the most portable & convenient Instrument accompanied with the Quicksilver horizon & stand, it constitudes a general or complete small portable Observatory The principle of it’s construction you will see is evidently the same as that of the Hadley’s Quadrant or Sextant but from it’s having three additional indices, when by a little practice you are acquainted with the ready management of the Instrument you will be enabled to detect & correct every possible Error of the Instrument however well it may be made viz: the Error of the center (if any) by reading off at the 3 parts of the Limb; the inequality of the divisions (if any) by changing the positions of the indices and the Errors of the Dark Glass Shades by turning the Glasses half from each angle. After your acquaintance with the particulars I have no doubt of your approving of the Instrument & it’s being adopted to your purpose. To the Box Sextant I have placed platina Limb which is a harder metal than Gold or Silver & will under the fine divisions by time less liable to be defaced We doubt not but these articles will arrive to you perfectly safe, and hope they will give you full satisfaction & merit the faver of your future commands.
I have the Honor to be, Sir, With much Respect Your obliged hble Servt
DLC: Papers of Thomas Jefferson.
Presidt Thos Jefferson London Octr 17th. 1807
Bought of W. and S. Jones
Optical and Mathematical Instrument Makers,
N. 30, Opposite Turnivals Inn, Holborn.
Removed from their old Shop No. 135, nearly opposite.
|A 10 Inch Reflecting Circle with 3 indices best graduation, Telescopes & in Case||}||18||18|
|A Brass Portable Stand & counterpoise for Do in a mahogany Case|
|A parl: Glass Roof Cover with brass frame and Trough for artificial Horizon||}||2||2|
|Quicksilver & box funnel Case for Do||10||6|
|A 3 Inch pocket Box Sextant with platina arch & angl. engrav’d Table||}||3||6|
|A Set of Keith’s Parallel Scales in ivory||1||1|
|A Case for Do||2|
|A Pair of hair Compasses||7||6|
|A Pair of Ditto wh screw||9|
|A Twelve Inch Concave Mirror||2||5|
|A Packing Case||4|