Philosophical Transactions of the Royal Society Part 18

On the 19. of _January_ 1665. _Stylo Angliae_ (or _Jan._ 29. 1666. _stylo novo_) at divers places neer _Oxford_, was observed a small _Earthquake_ (as at _Blechington, Stanton-St. Johns, Bril_, &c.) towards evening. In _Oxford_ it self, I doe not hear, that it was observ'd to be an Earthquake; yet I remember about that time (whether precisely then or not; I cannot say) I took notice of some kind of odde shaking or heaving I observed in my study, but did impute it to the going of Carts or Coaches, supposed to be not far off; though yet I did take notice of it, as a little differing from what is usual on such occasions; (and wondered the more, that I did not hear any:) But not knowing, what else to refer it to, I thought no more of it. And the like account I have had from some others in _Oxford_, who yet did not think of an Earth-quake; it being a rare thing with us. Hearing afterwards of an Earthquake observed by others; I looked on my Notes concerning my _Thermoscope_ and _Baroscope_, to see if any alteration considerable had then happened.

My _Thermoscope_ consists of a round large Gla.s.s, containing about half a pint or more; from whence issues a long Cylindrical neck of Gla.s.s, about two foot and a half in length, and less than a quarter of an inch diameter; which neck was _hermetically_ sealed at the top, to exclude communication with the External Air; but before the sealing of it, the whole Gla.s.s was filled with _Spirit of Wine_ (tinged with _Cochineel_, to make it the more discernable to the Eye) so warmed, that it filled the whole content of the Gla.s.s; but afterwards, as it cooled, did so subside, as to leave a void s.p.a.ce in the upper part of the Neck. Which Instrument, so prepared, doth by the rising or falling of the tinged liquor in the neck (consequent upon the expanding or contracting of the whole liquor contained in it and the Ball below) give a very nice account of the Temperature of the Air, {167} as to _Heat_ or _Cold_: Even so nice, as that my being or not being in my Study I find to vary its hight sometimes almost a quarter of an inch.

My _Baroscope_, I call another Instrument for estimating the _Weight_ or _Pressure_ of the Inc.u.mbent Air, consisting of a long _Gla.s.s-tube_ of about 4. foot in length, and about a quarter of an inch Bore: which tube (_hermetically_ sealed at the one end) being filled with Quicksilver (according to the _Torricellian_ Experiment) is inverted, so as to have the open end of it immersed in Stagnant Quicksilver, contained in a larger Gla.s.s under it, exposed to the pressure of the outward Air: Out of which open end (after such immersion) the Quicksilver in the Tube being suffered to run out, as much as it will, into the Stagnant Quicksilver, in which that mouth or open end is immersed, there is wont to remain (as is commonly known to those acquainted with this Experiment) a Cylinder of Quicksilver suspended in the Tube, about 28, 29, or 30. inches high; measuring from the surface of the Stagnant Quicksilver perpendicularly; (but more or less, within such limits, according as the Weight or Pressure of the Air inc.u.mbent on the External Stagnant Quicksilver exposed to it, is greater or less:) leaving the upper part of the Tube void. (Both which Instruments being the contrivance of the Honourable _Robert Boyle_, they are by him more particularly described in his _Physico-Mechanical Experiments touching the Air, Exper._ 17. and 18. and in his _Thermometrical Discourses_, premised to his _History of Cold_.)

Now, according to both these Instruments, having kept a daily _Register_ of Observations for more than a whole year (saving when I have been for some short time absent from home) I find my Notes for that day to be these.

_January._ |_Thermoscope._|_Baroscope._ 1665/6.

Day. Hour. | inches. | inches.

19. 8. Morn. | 14-1/16. | 29-1/2. Hard frost. Close.

4. Even. | 14-3/8. | 29-1/4. Hard frost. Cloudy.

9. Even. | 14-3/4. | 29-3/4. Rain. Wind 20. 8. Morn. | 15-1/4. | 28-3/4. Sunshine. Wind.

So that, there being in the morning (_January_ 19.) a hard frost (which began the day before about 4. of the Clock in the {168} 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 1/8 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._ 15 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 inc.u.mbent 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, 29-15/16, 29-7/8, 29-13/16 but never so low, all that time, as 29;) 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 Gla.s.ses, 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 29, in the forenoon; and afternoon, to 29-11/16. about the time the frost began: And _Jan._ 19. it was, at 8. in the morning, come down to 29; at 4. in the afternoon, to 29. But at 9. in the evening (when the Earth quake had intervened) it was risen half an inch, _vid._ to 29.

And, by the next morning, fallen again a whole inch, _vid._ to 28; 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 {169} 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. {170}

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 circ.u.mstances 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.

In _thick foggy_ weather, I find my Quicksilver to rise; which I adscribe to the heaviness of the Vapours in the Air. And I have never found it higher, than in the foggy weather above-mentioned.

In _Sunshiny_ weather it riseth also (and commonly the clearer, the more;) which, I think, may be imputed _partly_ to the Vapors raised by the Sun, and making the Air heavier; and _partly_ to the Heat, increasing the Elastick or Springy power of the Air. Which latter I the rather add, because I have sometimes observed in Sunshiny weather, when there have come Clouds for some considerable time (suppose an hour or two) the Quicksilver has fallen; and then, upon the Suns breaking out again, it has risen as before.

In _Rainy_ weather, it useth to fall (of which the reason is obvious, because the Air is lightned, by so much as falls:) In _Snowy_ weather, likewise, but not so much as in _Rain_. And sometimes I have observed it, upon a _h.o.a.r-frost_, falling in the night.

[Sidenote: * _The Author of these Observations intends hereafter more particularly to observe, _from what points_ those Winds blow, that make the Quicksilver thus subside._]

For _Windy_ weather, I find it _generally_ to fall; and that more universally, and more discernably, than upon Rain: (which I attribute to the Winds moving the Air _collaterally_, and thereby not suffering it to press so much _directly_ downwards: the like of {171} which we see in swimming, &c.) And I have never found it lower than in high Winds.*

I have divers times, upon discerning my Quicksilver to fall without any visible cause at home, looked abroad; and found (by the appearance of broken Clouds, or otherwise) that it had rained not far off, though not with us: Whereupon, the Air being then lightened, our heavier Air (where it rained not) may have, in part, discharged it self on that lighter.

_A more particular Account of those Observations about _Jupiter_, that were mentioned in _Numb. 8_._

Since the publishing of _Numb._ 8. of these _Transactions_, where, among other particulars, some short Observations were set down touching both the _shadow_ of one of _Jupiter's Satellits_, pa.s.sing over his Body, and that _Permanent Spot_, which manifests the Conversion of that Planet about his own _Axis_; there is come to hand an _Extract_ of that Letter, which was written from _Rome_, about those Discoveries, containing an ample and particular Relation of them, as they were made by the Learned _Ca.s.sini_, Professor of _Astronomy_ in the University of _Bononia_. That _Extract_, as it is found in the _French Journal des Scavans_ of _Febr._ 22. 1666. we thus _English_.

Monsieur _Ca.s.sini_, after he had discovered (by the means of those Excellent Gla.s.ses of 50. _palmes_, or 35. _feet_, made by M. _Campani_) the _Shadows_, cast by the 4 Moons or _Satellits_ of _Jupiter_ upon his Diske, when they happen to be between the Sun and Him; after he had also distinguished their Bodies _upon_ the Diske of _Jupiter_; made the last year some Praedictions for the Months of _August_ and _September_, noting the dayes and hours, when the Bodies of the said _satellits_ and their _Shadows_ should appear upon _Jupiter_, to the end that the Curious might be convinced of this matter by their own Observations.

Some of these Praedictions have been verified not only at _Rome_, and in other places of _Italy_, but also at _Paris_ by M. _Auzout_, the most Celebrated and the most Exact of our _Astronomers_; and in _Holland_, by M.

_Hugens_. And we can now doubt no longer, of the rotation of the _Satellits_ about _Jupiter_, as the Moon turns about the Earth; nor believe, that _Jupiter_ or his _Attendants_ have any other Light, than that, which they receive from the Sun; as some did {172} a.s.sure before these Observations. There remained to find by Experience, whether _Jupiter_ did turn about his _Axis_, as many believe, that the _Earth_ turns about her's. And although most _Astronomers_ had conjectur'd, it did so, either by this a.n.a.logy, or by other Congruities, yet it was much wish'd, that we might be a.s.sured thereof by Observations. And this it is, for which we are obliged to M. _Ca.s.sini_, who, having by the advantage of the same Gla.s.ses discover'd several changes, as well in the three obscure _Belts_, commonly seen in _Jupiter_, as in the rest of his _Diske_, and having also observed Spots in the midst of that _Planet_, and sometimes _Brightnesses_, such as have bin formerly seen in the _Sun_, hath at length discover'd a _Permanent Spot_ in the _Northern_ part of the most _Southern_ Belt; by the means whereof, he hath concluded, that _Jupiter_ turns about his _Axis_ in 9.

hours, 56. minutes, and makes 29. whole circ.u.mvolutions in 12 dayes 4.

minutes of ours, and 360 in 149. dayes. For he has found, that this _Spot_ was not caused by the Shadow of any _Satellit_, as well by reason of its Situation, as because it appeared, when there could be no Shadow. Besides, that its motion differed from that of the Shadows, which is almost equal, as well towards the Edges as towards the Middle of _Jupiter_: Whereas, on the contrary, this _Spot_ hath all the accidents, that must happen to a thing, which is upon the surface of a round Body moving; for example, to move much more slowly towards the Edges, than towards the Middle, and to pa.s.s over that part, which is in the middle of the Diske, equal to the half of the _Diameter_, in the sixth part of the time, it takes to make the whole revolution: he having seen this half pa.s.s'd over, in 99 or 100 minutes just, as it must happen, supposing the whole circ.u.mrotation is made in 9. hours 56. minutes.

He hath not yet been able to determine the Situation of the _Axis_, upon which this motion is made, because the _Belts_, according to which it is made, have for some years appeared streight, though in the precedent years, other _Astronomers_ have seen them a little crooked: Which sheweth, that the _Axis_ of the diurnal motion of _Jupiter_ is a little inclined to the plain of the _Ecliptick_. But in time we may discover, what certainty there is in this matter.

[Sidenote: _These _Tables_ are not yet sent over, but, 'tis hoped, will be, ere long._]

After this excellent Discovery, he hath calculated many _Tables_, whereof he gives the Explication and Use in the Letters by him addressed to the Abbot _Falconieri_. By the means of them, one may know, _when_ this _Spot_ may be seen by us. For, having first {173} considered it in relation to the _Sun_, in respect whereof, its motion is regular, he considers the same in relation to the _Earth_, where _We_ observe it; and shews by the means of his _Tables_, what is to be added or subtracted, to know, at what time the said _Spot_ is to come into the middle of _Jupiter_'s Diske, according as he is Oriental or Occidental. He hath also considered it in relation to an unmovable point, which he has supposed to be the first point of _Aries_, because we thither refer here upon Earth the beginning of all the Celestial motions, and _there_ is the _Primum mobile_, that one would imagine, if we were in _Jupiter_, as we do here imagine Ours of 24. hours.

The Discovery is one of the best, that have been yet made in the Heavens; and those, that hold the Motion of the earth, find in it a full a.n.a.logy.

For, _Jupiter_ turning about the Sun, does nevertheless turn about his _Axis_; and although he be much bigger than the Earth, he does nevertheless turn much more swiftly than it, since he makes more than two Turns, and a third part, for its one; and carries with him 4. Moons, as the Earth does one.

This Observation ought to excite all Curious persons to endeavour the perfecting of _Optick Gla.s.ses_, to the end that it may be discovered, whether the other _Planets_, as _Mars_, _Venus_ and _Mercury_, about whom no Moon hath as yet been discovered, do yet turn about their _Axes_, and in how much time they do so; especially _Mars_, in whom some _Spot_ is discover'd, and _Venus_, wherein M._Burattini_ hath signified from _Poland_, he has observ'd Inequalities, as in the Moon.

It will be worth while, to watch for the seeing of _Jupiter_ again this Spring, that this happy Observation may be confirmed in divers places, and endeavours used to make new ones.

_An Account of some Books, lately published._

I. _Hydrostatical Paradoxes, made out by New Experiments (for the most part Physical, and Easie) by the Honourable Robert Boyle._ This Treatise, promised in _Numb._ 8. of these Papers, is now come forth: And was occasioned by the perusal of the Learned Monsieur _Paschalls_ Tract, _Of the aequilibrium of Liquors_, and of the _Weight of the Air_: Of which two Subjects, the _latter_ having been more clearly made out in _England_ by Experiments, which could not be made by Monsieur _Paschal_ and others, that wanted the advantage of such Engines and Instruments, as have here been frequently made use {174} off; Our n.o.ble Author insists most upon giving us his thoughts of the former, _videl._ the _aequilibrium of Liquors_: Which Discourse consisting partly of _Conclusions_, and partly of _Experiments_, the _former_ seem to Him to be almost all of them consonant to the Principles and Laws of the _Hydrostaticks_; but as for the _latter_, the Experimental proofs, offered by M. _Paschall_ for his Opinions, are by our Author esteemed such, that he confesses, he hath no mind to make use of them: for which he alledges more reasons than one; which, doubtless, will appear very satisfactory to Intelligent _Readers_.

Wherefore, instead of the those _Paschalian_ Experiments, there is in this _Treatise_ deliver'd a far more Expeditious way, to make out, _not only_ most of the _Conclusions_, agreed on these two Authors, _but_ others also, that M _Paschall_ mentions not: and that with so much more ease and clearness, that persons, but ordinarily versed in the common principles of _Hydrostaticks_, may readily apprehend, what is deliver'd, if they will but bring with them a due Attention, and Minds disposed to prefer Reason and Experience to Vulgar opinions and Authors.

It not being our _Authors_ present Task, to deliver a Body of _Hydrostaticks_, but only some _Paradoxes_, which he conceives to be proveable by his New way of making them out, he delivers them in as many distinct Propositions; after each of which, he endeavours, in a Proof, or an Explication, to show, both that it is true, and why it ought to be so.

The _Paradoxes_ themselves (after a premised _Postulatum_) are these:

1. That in Water, and other Fluids, the Lower parts are pressed by the Upper.

2. That a lighter Fluid may gravitate or weigh upon a heavier.

3. That, if a Body, contiguous to the Water, be altogether, or in part, lower than the highest level of the said Water, the lower part of the Body will be pressed upward by the Water, that touches it beneath.

4. That in the Ascension of Water in Pumps, &c. there needs nothing to raise the Water, but a Competent weight of an External Fluid.

5. That the pressure of an External Fluid is able to keep an Heterogeneous Liquor suspended at the same height in several Pipes, though these Pipes be of very different Diameters.

{175}

6. If a Body be placed under Water, with its uppermost Surface parallel to the Horizon; how much Water soever there may be on this or that side above the Body, the direct pressure susteined by the Body (for we now consider not the Lateral nor the Recoyling pressure, to which the Body may be exposed, if quite environed with Water) is no more, than that of a Column of water, having Horizontal Superficies of the Body for its Basis, and the Perpendicular depth of the Water for its height.

And so likewise,

If the Water, that leans upon the Body, be contained in Pipes open at both ends, the pressure of the Water is to be estimated by the weight of a pillar of Water, whose Basis is equal to the lower Orifice of the Pipe (which we suppose to be parallel to the Horizon) and its height equal to a perpendicular, reaching thence to the top of the Water; though the Pipe be much inclined towards the Horizon, or though it be irregularly shap'd, and much broader in some parts, than the said Orifice.