Thomas Jefferson as Weather and Climate Observer
On July 1, 1776, Jefferson, in Philadelphia as a Virginia delegate to the Second Continental Congress, began keeping a systematic record of weather observations. If he kept a regular weather record before that, it has not survived in the collections of his papers. He maintained his register of meteorological entries, with some significant gaps, until late June 1826, a few days before his death. He sometimes referred to this type of record as a “diary,” meaning a daily record of occurrences. (He did not keep a diary in the sense that many people now would use the word.)
What is in the Records?
In 1784, when Jefferson urged his friend James Madison to keep a weather diary, he said that it should be arranged in columns and should include the date; the temperature, barometric pressure, wind direction, and weather conditions at sunrise and 4:00 PM; and observations of plants, birds, and miscellaneous phenomena.
Jefferson varied what he himself recorded in different periods, however. He was persistent in generally making two observations a day, one in the morning around sunrise when he thought the temperature would be at its lowest, and another around 3:00 or 4:00 in the afternoon to get the high temperature. He usually noted the temperature and the conditions at the time of the observation (such as whether it was fair, cloudy, or raining). At times, as in the entries in the early part of the record in Philadelphia in July 1776, he made three or even four observations in a day. In some periods he noted other information also, such as barometric pressure, air moisture (hygrometer readings), wind direction and perhaps force, and precipitation. He sometimes noted conditions or events such as frost, or additional factors connected to weather and climate such as the first appearance of certain birds in the spring or the blooming or ripening of certain trees or cultivated plants. He drew vertical lines to make columns on the page and put each type of information in its own column. Less consistent, from period to period, was the order in which he put the columns across the page. Overall the manuscripts are very neat: Jefferson probably made use of his pocket notebooks, small ivory sheets that he could write on in pencil and then wipe clean, to note the readings from his instruments, which he then transferred to the paper.
Jefferson also recorded weather- or climate-related information in other manuscripts, including notes about particular topics and summary tables of collected data. Several of those documents will be added to this site going forward.
A Note on Jefferson
Abraham Lincoln knew that Thomas Jefferson was a slaveholder. Lincoln knew that whatever Jefferson may have said about the evils of slavery, he benefitted from it and did nothing to change it. But in the 1850s, Lincoln and his allies in the effort to limit slavery used the language of the Declaration of Independence and the Northwest Ordinance to argue that Jefferson at the time of the nation’s founding believed freedom was the natural condition of all people. They put the products of Jefferson’s mind and pen to use, knowing that had he been alive he would have objected, just as they would have rejected many of his opinions and found much of his conduct totally unacceptable.
We can do the same as Lincoln and his associates did, putting Jefferson to use without accepting all that he was or did. Jefferson’s collection of information about weather and climate is an important historical source for his period. It can also help us understand our own time by documenting changes over the last two centuries. And it should be kept in mind that as much as these are Jefferson’s records, he was not their sole creator. He incorporated data obtained by other observers, usually without identifying them. He relied on skilled people who crafted the instruments he used. He gained knowledge from others and was part of a network of investigators. Most fundamentally, he had the education and time needed to carry out these detailed observations and compilations of data only through the labor of many other persons, the majority of them enslaved and exploited without their consent. We can use these records the better to comprehend those people’s world as well as our own, appropriating, like Lincoln, Jefferson’s efforts for beneficial use.