Mount Pleasant January 24. 1796. Dear Sir 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 seem 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 Bottitourt, 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 by constant attention with repeated Observations, give me any claim to conclusions I may make some pretence to it, but my calculations & conclusions must stand the test of examination. Wishing however to leave as little as possible to Doubt & uncertainty, I determined to put this barometrical mode of calculation to what appeared to me a proper [undecipherable: Trial?], and accordingly placed two Barometers in [undecipherable] rooms at the Redsprings [undecipherable] below the other in the Height [undecipherable] feet above, and all many [undecipherable] during Winter & Summer, [undecipherable] their [undecipherable] [undecipherable] noting the Temperature of the Air by a Thermometer [undecipherable]. The Results they generally [undecipherable] — [4729 was 166] This induced me to doubt either my own accuracy or this mode of calculation in general. Tho the Memoirs of Le W^r De Lue & some others in the English Philosophical Transactions seem to justify much dependance 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 D^r Rittenhouse and M^r 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 their Trials in the lower part of the atmosphere, especially in a City filled with Smoak & various exhalations, by no means to be relied on as operating against the general principles of barometrical calculation. Their Assurances produced a Communication to the [undecipherable] 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 it, 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 shew a Range of 3 Inches, and it seems to be allowed that the rise & fall in the course of a year generally make this difference in the height of the Mercury. In Philadelphia the annual Range is not half this, much as appeared by your Note that the Barometer [undecipherable] [undecipherable] [undecipherable] While I was below behind the Mountains (11 days at [undecipherable] & 29 at the Redsprings) the Barometer varied at the former [undecipherable] 0.⁸⁸/100 and at the Latter only 0.⁹¹/100 although the Thermometer varied more than 30 degrees and we had the extremes of weather as to fair & dry or cloudy & 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 ⁹¹/100, [strikethrough: show] the Thermometer in the same time rising about 6 degrees. This was in the Calf-pasture about 20 miles from Staunton. Before the Gust the Barometer was at its highest point. To discover the cause of these differences on one & the other Side of the Alleganie 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 more elevation, if accurately ascertained, would afford astonishing Clue to a Discovery which might in its consequence be of more importance [than?] appears at first Sight. If we could collect an accurate meterological Journals during one & the Same year in the lower & higher parts of the Country, it would perhaps appear that the Barometer is proportionably less liable to variation in high than in low Countries, 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 recommendation to Gentlemen living among the Mountains probably would effect this desirable Purpose. I wish also to attain the height of Rockfish [undecipherable: Gap?] above the [undecipherable: Foot?] on each Side by [undecipherable] [undecipherable] [undecipherable] and that Country with [undecipherable] an Instrument Should think nothing of a Journey of 20 or 30 Miles on purpose. The Reason I have given [undecipherable: relative?] to the inaccuracies of the lower parts of the atmosphere induces me to wish for the Correction of my barometrical Measurements; I am not so anxious as to the higher Country, when the [undecipherable: readings?] of the Mercury justifies a Dependance on its accuracy. With a View to correct my mode of Calculation I have tried the Article by Don Ullon, [undecipherable] of the Barometer & M^r Charles [undecipherable: ascent?] in the Balloon as [undecipherable] by the fall in the mercury used 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 & candidly give me all the Information & advice that you find 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 Jon Williams