Thomas Jefferson inherited from his father a collection of surveying and scientific instruments. Little is known about this collection, which most probably was destroyed in the Shadwell fire of 1770. Jefferson later acquired a collection of “Mathematical Apparatus” which was one of the finest in the country. He purchased many of these instruments, which included telescopes, microscopes, thermometers, and globes, on his journey to London in the spring of 1786.
Jefferson particularly loved instruments useful in “Physicomathematics”—subjects like astronomy and optics that required mathematical calculation. He wrote in 1816, “We cannot know the relative position of two places on the earth, but by interrogating the sun, moon and stars.” Jefferson valued astronomy because it furthered his knowledge of the earth and of his country’s geography. With his telescopes and his theodolite—an instrument equipped with telescopes and used for measuring both horizontal and vertical angles—Jefferson observed solar eclipses, fixed the true meridian of Monticello, and calculated the positions of features in the surrounding landscape. Jefferson also owned a hand magnifier, which he used to observe botanical specimens and insects.