Contexts of Place and Time
Location and time are essential frames of reference in systematic examinations of weather and climate.
We experience weather and climate within regional and local geographical settings. The importance of some meteorological diaries lies in their creators having stayed put, systematically recording the weather in one spot over an extended period. Monticello was Jefferson’s base for the entire half-century span of his observation records—but he wasn’t only there. A characteristic of his records that distinguishes them from those of some other observers is that his official life took him to various locations during much of that span, and he recorded meteorological data at several of those places. Geography thus plays a particular role in this set of records. Jefferson recorded many readings in Philadelphia, Paris, and Washington, D.C.; for shorter periods in Williamsburg, Virginia, and Annapolis, Maryland; a significant number at his “retreat” of Poplar Forest in Bedford County, Virginia; and occasionally at other locations. When he resided in Philadelphia or Washington he went back to Monticello when official business would allow. His weather observations have an itinerant quality, shifting scenes without notice. Moreover, he occasionally incorporated into his record information he acquired from other places, whether Bath, Maine, or Poughkeepsie, New York.
For any date that Jefferson entered in his daily observation registers, even if he recorded no meteorological data, we have assigned a location; in some cases all we can determine is that he was between two places as he traveled. (An essential resource in tracking the movements of the peripatetic Jefferson are his account books, published as his Memorandum Books, Volume 1, 1767–1790, and Volume 2, 1791–1826.)
Weather is closely tied to time as well as to place. Jefferson and others kept weather diaries, and meteorological data is studied today, because the weather changes with time. As the historian of science Jan Golinski, applying concepts of the philosopher Michel Serres, has noted, weather diarists beginning in the 17th century were putting weather into its “temporal framework,” aligning it against a “uniform timescale.” Golinski writes that “one might say that ‘the weather’ as we understand it—as a quotidian occurrence—was constituted through regular record-keeping governed by the clock and calendar.” To understand both weather and climate, to know what factors influenced them and to try to predict what would occur in the future, one needed to study it within the framework of time.
The chronological element in Jefferson’s weather records can be thought of as having three forms:
Time as duration. Jefferson’s weather registers, and others like them, accrued information day by day by day, running to months and then years. They enabled the user to compare one day’s conditions to the previous day’s, one week’s to the previous week’s, a recent winter, spring, summer, or autumn to one from years earlier or to a series of years. Information compiled over the longer runs of time gave indications not just of patterns of weather, but of climate. This aspect of time as continuum and duration is what we might call calendar time. “Those who systematically collected weather records adopted the uniform timescale of the civic calendar,” Golinski notes, which gave individuals control over the data they compiled and enabled them to share information in a meaningful way.
Time as cycles. Jefferson, like some other keepers of meteorological observation records, had a sophisticated understanding of astronomy and the annual movement of the Earth relative to the sun that causes seasonal changes in temperate zones. A meticulously maintained weather diary tracks the regular fluctuations in temperature associated with the seasonal cycle (and, depending on the record, perhaps other categories of information that might be subject to seasonal patterns, such as precipitation). Seasonal rhythms also have a place in Jefferson’s registers in the form of notations about the appearance of migratory birds in the spring, the blossoming and leafing out of trees in the spring and loss of their leaves in the autumn, the first availability of certain produce in the spring, and other observations of plant and animal life. Those were not observations of weather, but were another aspect of Jefferson’s and others’ plotting of events of the discernible world against the passage of time. The calendar was a useful tool for managing the study of recurring cyclical events, as it was for organizing data assembled over duration of time.
Time as increments of days and hours. When Jefferson started his keeping of a weather diary in Philadelphia in July 1776, he made as many as four observations a day and noted their times with some care. Some readings he recorded as 6:00 AM or 7:00 PM, which might imply that he made only a rough estimation of the time, except other observations in the same period he noted more precisely: 5:35 AM, 9:40 AM, 4:45 PM, 8:15 PM. Such measurement of the passage of time through the day is the realm of the clock rather than the calendar. The timepieces with which to do it were, like other instruments, more widely available in Jefferson’s era than they had been earlier. After that initial period of his weather record-keeping, Jefferson settled into a general routine of two weather readings each day—one at sunrise, which he thought the best time to get the lowest temperature of a 24-hour cycle, and another around 3:00 or 4:00 in the afternoon when he thought the temperature would be at its highest—and he did not note the time of each reading. Although he gave up recording the time of each observation, he continued to give importance to making more than one observation each day to capture low and high temperatures and other variations in conditions. He recognized, too, that weather is continuous, occurring at every moment and not infrequently changing in the course of a day. He worked out a system in his notation of weather conditions to record what had transpired during the interval between two points of observation: thus “c a r” meant that it was cloudy at the time of that observation, after rain that had fallen since the previous entry in the record.
Jan Golinski, British Weather and the Climate of Enlightenment (Chicago, 2007), 77-9, 94.