In Lancaster, Pennsylvania, master surveyor and cartographer Andrew Ellicott gives a letter to Meriwether Lewis who will soon deliver it to Robert Patterson in Philadelphia. In the letter, Ellicott discusses a key component of an artificial horizon.
Artificial Horizon using Water
Drawing by Robert N. Bergantino.
This is one of three types of artificial horizons described by Lewis on 22 July 24:
An Artificial Horizon on the construction recommended and practiced by Mr. Andrw. Ellicott of Lancaster, Pensyla., in which water is used as the reflecting surface; believing this artificial Horizon liable to less error than any other in my possession, I have uniformly used it when the object observed was sufficiently bright to reflect a distinct immage; but as much light is lost by reflection from water I found it inconvenient in most cases to take the altitude of the moon with this horizon, and that of a star impracticable with any degree of accuracy.
Lancaster May 7th 1803
Dear Sir
This will be handed to you by my friend Captn. Lewis Secretary to the President of the U.S.
I have forwarded by this opportunity the apparatus for forming the artificial horizon, with some remarks relative to its use. The talc is very delicate, and easily injured,—it should therefore be handled with caution. And for fear of accidents the person using the apparatus should not be without some spare pieces.
I am with great esteem you friend and Hbl. Servt.
Andw. Ellicott
