Jefferson’s daily weather observation records are tabular in format and contain nearly 19,000 observation points. Over the years, as he refined his method and added or subtracted instruments and information, Jefferson changed the arrangement of his tables. The date, though mostly recorded in a column on the left, sometimes appeared between the morning and afternoon observations. Conditions, while mostly in a column of their own, were also included with other observations or notes. In some periods he used a barometer, hygrometers, precipitation gauges, or wind instruments in addition to his thermometer, and in other periods he did not. His use of column headings to label the categories of data also varied. A full description of each manuscript may be found in the Documents section of the site.
Rather than attempt to replicate the layout of each manuscript page, we have transcribed the observations into a structured dataset that imposes a uniform format on the whole. The View Page option allows a comparison of each manuscript page with its standardized transcription.
Although his procedure sometimes varied, Jefferson’s usual practice was to make two observations each day, one around sunrise when he supposed the air temperature was lowest, and another at 3:00 or 4:00PM (depending on time of year) for the high temperature. In the structured transcription of this edition, each observation makes up an entry row in the dataset.
To enable each entry to be viewed independently and give uniformity to the content, some categories of information have both a transcription field, which reproduces what Jefferson wrote in the manuscript, and a data field, in which the content is provided in standardized searchable format and missing information is supplied. For example, a temperature that he wrote as “-14° F” will appear in that form in the transcription view, but as “-14” in data views. Similarly, we have supplied the full date and geographical location in data fields to attach that essential information to each observation entry. Values in the data fields are drawn on in searches and data visualizations.
The following example illustrates this complementation of the transcription by data fields. In his record for the afternoon of 25 June 1799, Jefferson omitted the location; recorded the date only as “25”; noted the general conditions as “f”; and recorded the temperature as 91½ and the barometric pressure as .40. (In noting air pressure, he did not repeat the digits to the left of the decimal point if they had not changed from the previous reading in his record.) In transcription view, the location is blank and the date, temperature, and barometric pressure appear exactly as he wrote them. In data views, such as when the entry appears in the results of a search, the date appears in full; the place (in this case Monticello) is supplied; Jefferson’s “f” abbreviation for conditions is expanded to “fair”; temperature has the value 91.5; and the barometric pressure is given in full as 28.40. (Jefferson also recorded a reading of 76 from a De Luc hygrometer, which appears in the transcription; but as explained below, we have not provided data fields for his air moisture observations.)
We have not supplied data fields for:
- Reaumur Temperature: Jefferson did not record many temperatures using the French Reaumur scale. When he did, the reading has been converted to Fahrenheit and included in the Fahrenheit data column.
- Hygrometer Readings: many hygrometers in Jefferson’s time relied on such measures as variations in the length of human or animal hair to determine levels of air moisture. Scales were not standardized, and precise calibration to enable comparisons of data was not possible. We have transcribed Jefferson’s hygrometer figures, and identified them by the type of device as he did (that is, Deluc or Saussure, or in Washington in the period November 1806–March 1809, unspecified).
- Wind Force: as was the case with hygrometers, instruments to measure wind force were highly individualized, not conforming to a reliable standard. Wind force has been transcribed as Jefferson recorded it, but does not appear in a separate data column.
Jefferson tended not to make separate columns for precipitation or snowfall amounts, but he sometimes noted such data in his notes of general observations. When he did that, we have put the amounts (in decimal inches) into data fields for precipitation and snow depth. The data field for precipitation amount contains only daily recordings of rainfall and snowfall converted to liquid amount. If Jefferson tallied the daily quantities into weekly or monthly totals of precipitation, those have been transcribed as independent documents.
The data column for time supplies the hour if Jefferson included the information in a column header or noted it directly at the observation; otherwise the editors have supplied AM for the early observation on the day or PM for the second observation.
General notations by Jefferson relating to the weather have been transcribed in the notations field as he wrote them. When he recorded an observation on a line in his manuscript with multiple observations on a day, the notation is attached to the last observation.
Notations by Jefferson describing his method or explaining something about the data have been transcribed in a field for Jefferson’s notes. If he used asterisks or a brace to apply such a note to a series of readings, we have transcribed his notation at the first entry and repeated it, enclosed in square brackets, in the others. In this way the relevant note by Jefferson appears even if the user views the entry outside the context of the manuscript page.
Memoranda by Jefferson in the pages of the daily observation records that do not apply to a single observation or an easily defined group of observations have been transcribed as separate documents. Examples are Explanation of Rain Gauge, Summer 1809 and Calculations of Precipitation, January–March 1811.
In his tables of his own observations Jefferson sometimes incorporated data from other locations that he picked up from newspapers or other sources. Although he noted those alongside his own readings for those dates, in this edition they appear as their own entries.
Each entry contains a field for observer, which in most cases was Jefferson. If an observation in his records could not have been made by him (such as when he was not in the location on that day) but must have been made under his direction, we have listed the observer as “Jefferson’s proxy.” (Every entry in his daily observation records is in his handwriting, meaning that in such instances he must have copied the information from his proxies’ notes.) If observers other than Jefferson can be identified, they are named in the observer field, otherwise they are listed as “unidentified.”
In our transcriptions of Jefferson’s daily observation records and other documents we have followed these procedures:
Abbreviations, capitalization, punctuation, and spelling have been retained as written.
Text in square brackets has been supplied by the editors and falls into two categories: to set off text that we have supplied for missing or illegible matter; and when Jefferson used an asterisk or “do.” (for “ditto”), we have used brackets to enclose an explanatory note or show the text that Jefferson was repeating from another entry.
We have ignored Jefferson’s strike-throughs in cases of routine corrections or changes. If a cancellation is significant, the struck-through text is shown as italic type within angled brackets, for example: <exactly 4 times>.