I know not, whether it will be worth while to add, that since I was oblig'd to leave London, I have been put upon so many lesser removes, that I have not been able to make Baroscopical Observations with such a constancy, as I have wished, but, as far as I remember, the Quick-silver has been for the most part, so high, as to invite me to take notice of it; and to desire you to do me the favour to inquire among your correspondents whether they have observ'd the same thing. * For, if they have, this lasting (though not uninterrupted) Altitude of the Quick-silver, happening, when the Seasons of the year have been extraordinary dry (so much as to become a grievance, and to dry up, as one of the late Gazettes informs us, some springs near Waymouth, that used to run constantly) it may be worth inquiry, whether these obstinate Droughts, may not be cleaving of the ground too deep, and making it also in some places more porous and as it were, spungy, give a more copious Vent, than is usual, to subterraneal steams, which adscending into the Air, increase the gravity of it. The inducements I have to propose this inquiry, I must not now stay to mention. But perhaps, if the Observation holds, it may prove not useless in reference to some Diseases.
* See Number 9. Phil. Transact. p. [157]. 5. 8 & 9. where the Word, Generally, signifies no more, than for the most part.
Perhaps it will be needless to put you in mind of directing those Virtuosi, that may desire your Instructions about Baroscopes, to set down in their Diarys not only the day of the month, and the hour of the day, when the Mercuries height is taken, but (in a distinct Columne) the weather, especially the Winds, both as to the Quarters, whence they blow (though that be not always so easy nor necessary,) and as to the Violence or Remisness, wherewith they blow. For, though it be more difficult,
than one would think, to settle any general rule about the rising and falling of the Quick-silver; yet in these parts one of those, that seem to hold oftnest, is, * that when high winds blow, the Mercury is the lower; and yet that it self does sometimes fail: For, this very day (March 3.) though on that hill, where I am, the somewhat Westerly Winds have been blustering enough, yet ever since morning the Quick-silver has been rising, and is now risen near ⅜ of an Inch.
I had thoughts to add something about another kind of Baroscope (but inferiour to that in use) whereof I have given some intimation in one of the Præliminaries to the History of Cold. But you have already too much of a letter, and my occasions, &c.
* Dr. Beale concurs with this Observation, when he saith, in a late Letter of March 19. to his Correspondent in London; By change of Weather and Wind, the Mercury is sunk more than an Inch, since I wrote to you on Munday last. March 12. This last night, by Rain and South wind, 'tis sunk half an Inch.
So far that Letter. Since which time, another from the same Noble Observer intimates, That, as for that cause of the height of the Quick-silver in Droughts, which by him is suspected to be the elevation of steams from the Crust or Superficial parts of the Earth, which by little and little may add to the Weight of the Atmosphere, being not, as in other seasons, carried down from time to time by the falling Rain, it agrees not ill with what he has had since occasion to observe. For, whereas about March 12th, at Oxford, The Quick-silver was higher, than, for ought he knew, had been yet observ'd in England, viz. above 5/16 above 30. Inches, upon the first considerable showers, that have interrupted our long Drought, as he affirms, he foretold divers hours before that the Quick-silver would be very low, (a blustering Wind concurring with the Rain) so he found it at Stanton to fall ⅜ beneath 29. Inches.*