From Jonathan Williams
Mount Pleasant January 24. 1796.
As you are now retired from public Business you will not, probably, consider a philosophical communication as an unpleasant Intrusion on your Leisure; If, however, I were to offer an Apology, it would be the Experience I have had of your Indulgence in many Conversations. In the Summer of 1791 I went with my Family to the Redsprings in Bottetourt, and took with me the best Thermometer and Barometer I could procure. With these Instruments I intended to estimate the Height of the Country as I passed, and if constant attention with repeated Observation give me any claim to confidence, I may make some pretence to it; but my calculations and conclusions must stand the test of examination. Wishing however to leave as little as possible to doubt and uncertainty, I determined to put this barometrical mode of Calculation to what appeared to me a proper Trial, and accordingly I placed two Barometers in Christ Church, one at the Pulpit below, the other in the steeple 166 feet above, and at many periods, during Winter and Summer, I examined their relative State, noting the Temperature of the Air by a Thermometer both above and below. The Results these gave by barometrical Calculation varied from 105 to 203 feet tho’ the known Height was 166. This induced me to doubt either my own Accuracy or this mode of Calculation in general tho’ the Memoirs of M. Du Luc and some others in the English Philosophical Transactions seem to justify much Dependence upon them. Under this Impression, I thought it better to be silent than to publish an Error, and my whole proceeding would have been unknown if in an accidental Conversation with Dr. Rittenhouse and Mr. Patterson they had not desired me to produce the Journal as it was, leaving it to others to comment upon it; assuring me at the same time that they thought these Trials in the lower part of the atmosphere, especially in a City filled with Smoke and various exhalations, by no means to be relied on as operating against the general principles of barometrical Calculation.
These Assurances produced a Communication to the Philosophical Society of which I inclose an Extract, with four Sections of some of the mountains, taking the Level of Richmond for the Basis. To this should be added the height of Richmond from the Sea, which I have not ascertained; but considering the current of James River, I suppose about 150 feet not far out of the way.
The English Barometer is graduated so as to show a Range of 3 Inches; and it seems to be allowed that the rise and fall in the course of a Year generally marks this difference in the height of the Mercury. In Philadelphia the annual Range is not half of this, and it appears by your Notes that the Barometer varied at Williamsburg but 1.86/100. in a Year and during 9 months at Monticello (about 500 feet higher) the difference between the two extremes was only 1.21/100. While I was stationary behind the Mountains (11 days at staunton and 29 at the Redsprings) the Barometer varied at the former place 0. 40/100 and at the latter only 0.20/100 although the Thermometer varied more than 30 degrees and we had the extremes of weather as to fair and dry or cloudy and heavy rain: In one day, after a very fine morning, we had the severest Gust I saw in that Country, which affected the Barometer only 43/100 the Thermometer in the same time rising about 6 degrees. This was in the Calfpasture about 20 miles from Staunton, and before the Gust the Barometer was at its highest point.
To discover the cause of these differences on one and the other side of the Atlantic we must probably have recourse to some general Law, perhaps the more prevalent humidity on one side than on the other; But I confess I am inclined to suspect that mere elevation, if accurately ascertained, would afford an interesting Clue to a Discovery which might in its consequence be of more importance than appears at first sight. If we could collect accurate meteorological Journals during one and the same Year in the lower and higher parts of the Country, it would perhaps appear that the Barometer is proportionably less liable to variation in high than in low Countries, and perhaps a place might be found where it would be always stationary: I need not mention to you some interesting Conclusions such an Experiment would produce. Your extensive acquaintance and the weight of your reccommendation to Gentlemen living among the Mountains probably would effect this desireable Purpose. I wish also to obtain the height of Rockfish Gap above the Foot on each side by a spirit Level; If I were in that Country with such an Instrument I should think nothing of a Journey of 20 or 30 Miles on purpose. The Reasons I have given relative to the inaccuraces of the lower parts of the Atmosphere, induce me to wish for this Correction of my barometrical Measurement; I am not so Anxious as to the higher Country, where the steadiness of the Mercury justifies a Dependance on its accuracy. With a View to correct my mode of Calculation I have tried the Andes by Don Ulloa’s state of the Barometer, and Mr. Charles Assent in the Balloon at Paris by the fall in the mercury noted by him, and my Results do not materially differ from those of these celebrated Men.
I shall take it as a Favour if you will kindly and candidly give me all the Information and advice that you think interesting on these Subjects, as I am desirous to have my Communication to the Society wholly suppressed at the Time of publishing the next Volume, unless the Opinion of able Men should justify its appearance among the Transactions. I am with great Respect Sir Your most obedient & most humble Servant
RC (CSmH); at foot of text: “The Hon Th: Jefferson.” Recorded in SJL as received on 10 May 1796.
Jonathan Williams (1750–1815), the son of a wealthy Boston merchant of the same name, received his education in that city and with the aid of Benjamin Franklin, his great uncle, gained further commercial experience in England, 1770–76, and France, 1776–85. He subsequently established himself as a merchant in Philadelphia, where he pursued an interest in science and was elected a secretary of the American Philosophical Society four times between 1791 and 1797, a councillor six times between 1798 and 1813, and a vice president in 1815. TJ appointed him superintendent of the U.S. Military Academy at West Point and inspector of fortifications, 1801–03 and 1805–12 (DAB description begins Allen Johnson and Dumas Malone, eds., Dictionary of American Biography, New York, 1928–36, 20 vols. description ends ; APS description begins American Philosophical Society description ends , Proceedings, xxii, pt. 3 , 187, 201, 211, 216, 246, 266, 290, 330, 392, 419, 438, 451).
Du luc: Genevan scientist Jean André Deluc (or De Luc) solved some of the problems that had made barometric observations since the seventeenth century inconsistent, including inaccurate instruments and the effects of temperature, and developed new methods and formulas for the measurement of elevations by barometer. His book, Recherches sur les Modifications de l’Atmosphere, 2 vols. (Geneva, 1772), fostered several papers in the philosophical transactions of the Royal Society of London for 1774 and 1777–79. The South American barometric readings of Antonio de Ulloa and Jorge Juan y Santacilia of Spain appeared in their Observaciones astronomicas, y phisicas; hechas de orden de S. Mag. en los reynos del Peru (Madrid, 1748), 102–31, which also described methods of calculating altitudes. Jacques Alexandre César Charles had taken barometric readings during an ascent to over 9,000 feet in a hydrogen balloon in France in 1783, as described in his Représentation du globe aérostatique: qui s’est elévé de dessus l’un des bassins du Jardin Royal des Thuilleries. Le 1er. Décembre 1783 (Paris, 1783). See Abraham Wolf, A History of Science, Technology, and Philosophy in the Eighteenth Century (New York, 1939), 288–302, 578; and sketches of Charles and Ulloa in DSB description begins Charles C. Gillispie, ed., Dictionary of Scientific Biography, New York, 1970–80, 16 vols. description ends , iii, 207–8, xiii, 530–1.
Communication to the Society: Williams had presented his findings, including “a journal of observations, “at a meeting of the American Philosophical Society on 20 Nov. 1795. As printed in the transactions of the society for 1799, the report consisted of a letter from Williams to Robert Patterson, one of the society’s secretaries, of 13 Nov. 1795, touching many of the points in Williams’s letter to TJ above; the tabular “journal” (see Enclosure i below); a diagram (see Enclosure ii below); and a “postscript” from Williams to Patterson, 18 Aug. 1796, containing an extract of TJ’s 3 July 1796 letter to Williams and mentioning problems associated with optical measurement of heights of mountains (“Barometrical Measurement of the Blue-Ridge, Warm-Spring, and Alleghany Mountains, in Virginia, taken in the Summer of the year 1791,” APS description begins American Philosophical Society description ends , Transactions, iv , 216–23; APS description begins American Philosophical Society description ends , Proceedings xxii, pt. 3 , 234–5).