Some Observations and Directions about the Barometer, Communicated by the Same Hand, to the Author of This Tract

disabled by sickness to come over to me (which he promis'd to do, as soon as he could) writ me only a Ticket, whose substance was, That the Earth-quake was there much more considerable, than where I lodged, and that at a Gentleman's house, whom he names (the most noted Person, it seems, of the neighbourhood) the House trembled very much, so as to make the Stones manifestly to move to and fro in the Parlour, to the great amazement and fright of all the Family. The Hill, whereon this Brill stands, I have observ'd to be very well stor'd with Mineral substances of several kinds; and from thence I have been inform'd by others, that this Earth-quake reach'd a good many miles; but I have neither leisure, nor inclination to entertain you with uncertain reports of the Extent and other Circumstances, especially since a little further time an inquiry may enable me to give you a better warranted account. Some Observations and Directions about the Barometer, communicated by the same Hand, to the Author of this Tract. These shall be set down, as they came to hand in another Letter; videl. As to the Barometrical Observations (as for brevities sake I use to call them) though you * guessed aright, that, when I saw those of the Learned and Inquisitive Dr. Beale, I had not Mine by me, (for I left them, some years since, in the hands of a Virtuoso, nor have I now the leisure to look after those Papers;) yet since by the Communication, you have made publick, 'tis probable, that divers Ingenious men will be invited to attempt the like Observations, I shall (notwithstanding my present haste) mention to you some particulars, which perhaps will not appear unseasonable, that came into my mind upon the reading of what you have presented the Curious. When I did, as you may remember, some years agoe, publicly express and desire that some Inquisitive men would make make Baroscopy Observations in several parts of England (if not in foreign Countries also;) and to assist them, to do so, presented some of my Friends with the necessary Instruments: The declared reason of my desiring this Correspondence was (among other things) that by comparing Notes, the Extent of the Atmospheric Changes, in point of Weight, might be the better estimated. But not having hitherto received some account, that I hoped for, I shall now, without staying for them, intimate thus much to you: That it will be very convenient, that the Observers take notice not only of the day, but, as near as they can, of the Hour wherein the height of the Mercurial Cylinder is observ'd: For I have often found, that within less than the compass of one day, or perhaps half a day, the Altitude of it has so considerably vary'd, as to make it in many cases difficult, to conclude anything certainly from Observations, that agree but in the day. It will be requisite also, that the Observers give notice of the Situation of the place, where their Barometers stand, not only, because it will assist men to Judge, whether the Instruments were duly perfected, but principally, because, that though the Baroscope be good (nay, because it is so) the Observations will much disagree, even when the Atmosphere is in the same state, as to Weight, if one of the Instruments stand in a considerably higher part of the Countrey, than the other. To confirm both the foregoing admonitions, I must now inform you, that, having in these parts two Lodgings, the one at Oxford, which you know stands in a bottom by the Thames side, and the other at a place, four miles thence, seated upon a moderate Hill, I found, by comparing two Baroscopes, that I made, the one at Oxford, the other at Stanton St. Johns, that, though the former be very good, and have been noted for such, during some years, and the latter was very carefully fill'd; yet by reason, that in the Higher place, the incumbent part of the Atmosphere must be lighter, than in the Lower, there is almost always ways between 2 and 3 Eight of an Inch difference betwixt them: And having sometimes order'd my servants to take notice of the Disparity, and divers times carefully observ'd it myself, when I pass'd to and fro between Oxford and Stanton, I generally found, that the Oxford Barometer and the other did, as it were by common consent, rise and fall together so, as that in the former the Mercury was usually $\frac{1}{8}$ higher, than in the latter. Which Observations may teach us, that the Subterraneous steams, which ascend into the Air, or the other Causes of the varying Weight of the Atmosphere, do, many times, and at least in some places, uniformly enough affect the Air to a greater height, than, till I had made this tryall, I durst conclude. But, as most of the Barometricall observations are subject to exception, so I found the formerly mentioned to be. For (to omit lesser variations) riding one Evening from Oxford to Stanton, and having, before I took horse, look't on the Baroscope in the former of these 2 places, I was somewhat surprised, to find at my comming to the latter, that in places no farther distant, and notwithstanding the shortness of the time (which was but an hour and a half, if so much) the Barometer at Stanton was short of its usual distance from the other, near a quarter of an Inch, though, the weather being fair and calm, there appear'd nothing of manifest change in the Air, to which I could adscribe so great a Variation; and though also, since that time, the Mercury in the two Instruments hath, for the most part, proceeded to rise and fall as before. And these being the only Observations, I have yet met with, wherein Baroscopes, at some Distance of Place, and Difference of Height, have been compar'd (though I cannot now send you the Reflexions, I have elsewhere made upon them;) as the opportunity I had to make them myself, rendred them not unpleasant to me, so perhaps the Novelty will keep them from being unwelcome to you. And I confess, I have had some flying suspicions, that the odd Phenomena of the Baroscope, which have hitherto more pos'd, than instructed us, may in time, if a competent number of Correspondents do diligently prosecute the Inquiries (especially with Baroscopes, accommodated with Mr. Hooks ingenious additions) make men some Luciferous discoveries, that possibly we do not yet dream off. 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 Baroscopic 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 Weymouth, that used to run constantly) it may be worth inquiry, whether these obstinate Droughts, may not by 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 subterranean steams, which ascending 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. 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 Mercures height is taken, but (in a distinct Column) 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 Remission, wherewith they blow. For, though it be more difficult, than *This hath been inquired into, and is found, that several Accurate and Curious persons (as the Most Noble President of the Royal Society, the Lord Viscount Brounker, Doctor Beale, Mr. Hook &c.) have observed the same. than onewould 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 oftneft, 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 \( \frac{3}{8} \) of an Inch. I had thoughts to add something about another kind of Baroscope (but inferior to that in use) whereof I have given some intimation in one of the Preliminaries to the History of Cold. But you have already too much of a letter, and my occasions, &c. 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 \( \frac{3}{8} \) 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 \( \frac{3}{8} \) beneath 29 Inches.* * 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 Monday last, March 12. This last night, by Rain and South wind,'tis sunk half an Inch. General