From Meriwether Lewis
Philadelpia, May 14th. 1803.
In your instructions to me you mention that the instruments for ascertaining by celestial observations the geography of the country through which I shall pass, have been already provided: I shall not therefore purchase any articles of that discription untill I hear further from you on this subject. Will you be so good as to inform me what instruments have been provided? and where they are?—it may be possible that some instrument has been omitted, which Mr. Patterson, Mr. Ellicott and those gentlemen to whom you have referred me in this place, may deem necessary for me, and if so the deficiency can be supplyed in time.—
Mr. Patterson and Mr. Ellicott both disapprove of the Theodolite as applicable to my purposes; they think it a delicate instrument, difficult of transportation, and one that would be very liable to get out of order; they also state that in it’s application to any observations for obtaining the Longitude, it would be liable to many objections, and to much more inacuracy than the Sextant—The instruments these gentlemen recommend, and which indeed they think indispensibly necessary, are, two Sextants, (one of which, must be constructed for the back observation,) an artificial Horizon or two; a good Arnald’s watch or Chronometer, a Surveyor’s Compass with a ball and socket and two pole chain, and a set of plotting instruments.—By means of the Sextant fixed for the back observation and an artificial Horizon also constructed for the purpose, the meridian altitude of the Sun may always be taken, altho it should even exceed eighty degrees: for this valuable problem I am indebted to Mr. Patterson.—
As a perfect knolege of the time will be of the first importance in all my Astronomical observations, it is necessary that the time-keeper intended for this expedition should be put in the best possible order, if therefore Sir, one has been procured for me, and you are not perfectly assured of her being in good order, it would be best perhaps to send her to me by some safe hand (should any such conveyance offer in time); Mr. Voit could then clean her, and Mr. Ellicott has promised to regulate her, which, I believe he has the means of doing just now, more perfectly than it can be done any where else in the UStates.—
I cannot yet say what day it will be in my power to leave this place.—Your different orders have been attended to, and the result you shall have in a day or two.—
I am Sir, with every sentiment of gratitude and respect—
Your most Obt. & very Humble Servt.
RC (DLC); at foot of text: “The President of the UStates”; endorsed by TJ as received 16 May and so recorded in SJL.