~/jeffreymoro/posts/2027-07-13-diptych.md
1. Thomas Jefferson
began keeping a weather diary on July 1st, 1776, while in Philadelphia at the Second Continental Congress. He had finished writing the lion’s share of the Declaration of Independence two days before. He was renting the second floor of 700 Market Street, a red brick three-story house constructed a year earlier. The diary at first comprised only three columns: the day, the temperature, and the time of its taking. He usually took two readings a day, one in the morning and one in the evening. On July 13th, 1776, at around 2 PM, the temperature in Philadelphia was 76 degrees Fahrenheit. Later in the evening, it rained. Jefferson continued to keep a weather diary with consistency for the subsequent fifty years. He never recorded an explanation for why he did so. In 1784, he wrote to James Madison and encouraged him to keep a weather diary as well. His rationale was simply that it might be “an amusement.”
There are, of course, a variety of reasons why he might have done so. Jefferson was a landowner and a slaveholder who derived a substantial portion of his income from agricultural pursuits. Knowledge of the weather would invariably be valuable not only for its own scientific sake, but also for practical applications in the growing of crops. The late eighteenth century was also a boon time for the early practice of meteorology. Early networks of weather enthusiasts began to emerge in the Colonies, members sharing their data with each other, prototypes of what would later in the mid-1800’s become the Smithsonian Institution’s endeavor to construe a national network of meteorological observations, itself a prototype in turn of the National Weather Service. Jefferson was a committed member of such early networks, and encouraged friends and mentees alike to keep weather diaries alongside him.
Some of those friends were open to the idea, but protested that they couldn’t do so for lack of any meteorological instruments. Thermometers and hygrometers were relatively new inventions, and any that worked with precision were fairly expensive, particularly out in the backwaters of the Colonies. On July 4th, 1776, three days after he began his weather diary, Jefferson purchased a thermometer from a merchant named John Sparhawk for three pounds and fifteen shillings. Calculating the rate of inflation over two hundred and fifty years is tricky, but that’s somewhere around $1,500 in 2026, depending on your math. (It would have gotten you, more or less, a healthy cow.)
Jefferson was a wealthy man: over his life he purchased twenty or so thermometers, alongside other instruments. He had two different hygrometers running simultaneously through much of the 1790s. One, designed by a Genevan named Jean-André Deluc, was made of ivory: a piece of whalebone in a tube expanded and contracted with the humidity, pushing mercury up the tube. The effect was not dissimilar to modern-day thermometers. The second, designed by another Genevan named Horace-Bénédict de Saussure, was made of hair: the hair would expand and contract with humidity, and a pulley system amplified the changes so that they would be visible on a round scale, graded from 0 (dry) to 100 (very not dry). The two men feuded bitterly over whose hygrometer was better: Deluc claimed that de Saussure’s hygrometer was unreliable at the extremes; de Saussure retorted that whalebone could never really dry out enough to be reset to a known zero. Really, the two men moved in the same scientific circles in Geneva and Deluc was a known controversialist: it’s just as likely that the root of his dispute with de Saussure was that he (Deluc) had spent a decade-and-a-half working on his hygrometer, and de Saussure’s was not only truly better, but moreover evinced a fuller theory of hygrometry more generally. History would eventually pick de Saussure’s hygrometer over Deluc’s, but in Jefferson’s time, there was enough evidence for both sides that he simply chose to use them both.
2. George Washington
also kept a weather diary, albeit with less consistency than did Jefferson. He did not seem to match Jefferson’s passion for instruments; he owned but one thermometer and rarely bothered with readings for humidity or barometric pressure. He also, it seems, did not quite know where to put it. There are references in his diaries to recording various temperatures and then moving the thermometer outside to see the difference; from this evidence, it’s difficult to say whether Washington kept his thermometers consistently indoors or outdoors.
But Washington may have simply been following the advice of the times. The thermometer, after all, was a new invention; and distinctions between indoor and outdoor temperatures were not as extreme as they are today. In a report published by the Royal Society, James Jurin, secretary, argued for placing thermometers inside homes on their north walls, as far away from the fireplace as possible. The idea was to limit any exposure to heat or sunlight, so as to achieve a truer, more neutral sense of the temperature. Several continental scientists disagreed heartily and vociferously; but it seems that their objections did not make it across the pond to Washington, who was happy to follow the Royal Society’s expert guidance.
Meanwhile, in Geneva, our friends Deluc and de Saussure were at it again. Deluc had published the claim that thermometers with isolated bulbs, touching absolutely nothing but glass, would give precisely the same temperatures whether in the sun or shade, and that these temperatures could be safely considered the true, valid temperatures for a time and place. de Saussure thought this plainly wrong, and demonstrated, through an experiment conducted on the side of the Mont Blanc massif, that in fact two identical thermometers, one placed in the sun and one nearby in the shade, would record two different temperatures. Deluc took it about as well as you’d expect, which is to say not well at all. He countered with an odd (even for the time) theory that when sunlight hits the mountain air, it excites the intrinsic fire in the air in such a way as to act upon thermometers in ways that explained de Saussure’s thermometers’ divergence. In reality, he was probably covering for the fact that his instruments didn’t work all that well.
Today, in Baltimore, the thermometer in my office reads just shy of 80 degrees Fahrenheit, and the barometer reads 30.35 inHg, although I’ve long suspected the barometer doesn’t work all that well, given that the whole piece is an antique. According to the Old Farmer’s Almanac I keep as bathroom reading, we have entered the dog days of summer. Sirius has risen, auguring heat, thunder, indolence, wantonness, and general bad luck. I hope for your sake you are spared at least a few of those; although another few might not be so bad all told.
PS. I learned that the search engine I use, Kagi, maintains a compendium of “Small Web” sites, personal blogs and the like, that you can page through at random. I did a search and my blog is in their index, which as a child of StumbleUpon brings me great joy. If you happen to have come across this blog thanks to this feature, do let me know.