afternoon (Jan. 18.) and continued (with us) till about 5. of the Clock in the afternoon of that day, Jan 19. with some fierceness) and the weather, Jan. 19. being in the morning, close; and cloudy all the day, with little of Sun-shine; the Liquor in the Thermoscope was very little raised, by 4. of the Clock afternoon, that is, but 5/16 of an inch (which, had the Sun shone, would, it's likely, have been near an Inch:) and after that time (or somewhat before) had there been no considerable change of weather, it would upon the Sun's setting have fallen (and probably so it did, till about 5. of the Clock, though I took no Observation in the interim.) But, contrary to what would have been expected, it was at 9. of the Clock at night, higher by ⅛ of an inch, than it had been at 4. occasioned by the change of weather, the Frost suddenly breaking, with us, between 5. and 6. of the Clock; about which time also it began to rain, and continued raining that Evening and good part of the Night. And the next morning I found the Liquor yet higher by half an inch, vid. 15¼ inches: (by reason of the Air that night being so much warmer, than it had been the day before;) whereas commonly it is considerably lower in the morning, than over night.
As to the Baroscope, for the Weight or Pressure of the Air; I find, that for the 11, l2, 13, 14, 15, 16, and 17. dayes, the Mercury in the Tube, was (by the ballancing Pressure of the incumbent Air on the stagnant Quicksilver, exposed to it) kept up to the height of near 30. Inches above the surface of the External Quicksilver, (though with some little variation, as 30, 2915/16, 29⅞, 2913/16 but never so low, all that time, as 29¾;) which is the greatest height I have know it at, (for I do not find that I have ever, till then, observed it to be, in my Glasses, full 30. Inches, though it have been very near it:) the Weather having been almost continually Foggy, or very thick Mists, all that time. January 18. it came down to 29¾, in the forenoon; and afternoon, to 2911/16. about the time the frost began: And Jan. 19. it was, at 8. in the morning, come down to 29½; at 4. in the afternoon, to 29¼. But at 9. in the evening (when the Earth quake had intervened) it was risen half an inch, vid. to 29¾. And, by the next morning, fallen again a whole inch, vid. to 28¾; which fall I attribute (at least in part) to the rain that fell in the night.
This being what I observed out of my Register of these Instruments, (which, if I had then thought of an Earthquake, I
should have more nicely watched) what I have further gathered from Reports, is to this purpose.
I hear, it was observed at Blechington, above 5. miles to the North of Oxford, and so along by Bostol, Horton, Stanton-St. Johns, and so towards Whately, which is about 4. miles Eastward from Oxford. Not at all these places at the same time, but moving forward from Blechington towards Whately. For it was at Stanton about 6. of the Clock or later (as I understand from Mr. Boyle, who was there at that time;) but had been at Blechington a good while sooner. And I am told, that it was taken notice of by Doctor Holder (a Member of our Society) who was then at Blechington, to be observed by those in the further part of the Garden, some very discernable time before it was observed by those in the House; creeping forward from the one place to the other. What other places in the Country it was observed at, I have not been informed: but at Oxford (which, it seems, was about the skirts of it) it was so small, as would have been hardly noted at all, had not the notice, taken of it abroad, informed us of it.
Upon this Occasion, it will not be unseasonable to give some General accounts of what I have in my Thermoscope and Baroscope observed.
My Thermoscope, being fitted somewhat at adventures, I have found at the lowest to be somewhat more than 12. inches high, in the fiercest time of the long Frost in the beginning of the last year 1665. and about 27. Inches high, at the highest, in the hottest time of the last Summer: (which I mention, that it may appear at what temperature in proportion, the Air was at the time above-mentioned.) But I must add withall, that this standing so, as never to be exposed to the Sun, but in a room, that has a window only to the North, it would have been raised much higher than 27. inches, if it were put in the hot Sun-shine in Summer; this, as it is placed, giving therefore an account onely of the Temperature of the Air in general, not of the immediate heat of the Sun-shine.
This Instrument, thus situated, when it is about 15. inches, or lower, is for the most part hard frost; but seldom a frost, if higher than 16. Yet this I have often observed, that the Air by the Thermoscope has appeared considerably colder (and the liquor lower) at sometimes when there is no Frost, than at some other times, when the Frost hath been considerably hard.
In my Baroscope, I have never found the Quicksilver higher than 30. inches, nor lower than 28. (at least, scarce discernably, not 1/16 of an inch higher than that, or lower than this;) which I mention, not only to shew the limits, within which I have observed mine to keep, vid. full 2 inches, but likewise as an Estimate of the Clearness of the Quicksilver from Air. For, though my Quicksilver were with good care cleansed from the Air; yet I find that which Mr. Boyle useth, much better: for, comparing his with mine at the same times, and both in Oxford, at no great distance; I find his Quicksilver to stand alwaies somewhat higher than mine (sometimes neer a quarter of an Inch;) which I know now how to give a more probable account off, than that my Quicksilver is either heavier than his; or else, that his is better cleansed from Air, (unless, possibly, the difference of the Bore, or other circumstances of the Tube, may cause the alteration; mine being a taller Tube, and a bigger Bore, than his.) And upon like reason, as his stands higher than mine; so another less cleansed from Air, may at the same time be considerably lower, and consequently under 28. Inches at the lowest.