University of Virginia Library

XIII. XIII

LEWIS TO JEFFERSON

XIII. [From original MS. in Bureau of Rolls—Jefferson Papers, series 2, vol. 51, doc. 98.]

Dear Sir: 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 until 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 my 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 Arnold'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
observations 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, ir
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 anywhere else in the U. States.

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