Provenance: Thomas Jefferson; by gift to Dr. Robley Dunglison; by descent to John Alden Tifft; by gift to the Historical Society of Pennsylvania in 1945; by purchase to Thomas Jefferson Foundation in 1999, made possible by a generous donation from the Melville Foundation.
Historical Notes: In his memorandum books Jefferson recorded the purchase of almost twenty thermometers. On July 4, 1776, he bought one from Philadelphia merchant John Sparhawk for £3-15. Three days earlier he had begun his first surviving "meteorological diary."1 For the rest of his life his daily routine included a thermometer check at dawn and in late afternoon — in his opinion, the coldest and warmest times of day. His temperature record was sometimes supplemented with barometer and hygrometer readings, as well as notes on what he called "indexes of climate," like the blooming of plants and migrations of animals.
As one of the first systematic observers of the American climate, Jefferson tried to enlist others in his activities and even envisioned a national network of weather watchers. He realized that, for the formation of a reliable theory of climate, many others would have to provide what he had: years of "steady attention to the thermometer, to the plants growing there, the times of their leafing and flowering, its animal inhabitants, beast, birds, reptiles and insects; its prevalent winds, quantities of rain and snow, temperature of mountains, and other indexes of climate."2
Marked "Jones & Sons/Holborn London," this thermometer is probably the one received from William Jones early in 1789. Jefferson had asked for a thermometer "not less than 18. inches long" for mounting outside a window, with Fahrenheit and Reaumur scales and graduations precise enough for occasional "nice" experiments.3
2. Jefferson to Lewis E. Beck, July 16, 1824, in L&B, 16:72. Transcription available at Founders Online.
3. Jefferson to William Jones, December 10, 1788, in PTJ, 14:346. Transcription available at Founders Online. See also Jones to Jefferson, January 2, 1789, in PTJ, 14:441. Transcription available at Founders Online.