an account of a new kind of baroscope, which may be called statical; and of some advantages and...

An Account of a New Kind of Baroscope, Which May be Called Statical; And of SomeAdvantages and Conveniencies It Hath above the Mercurial: Communicated, Some While Since,by the Honourable Robert BoyleAuthor(s): Robert BoyleSource: Philosophical Transactions (1665-1678), Vol. 1 (1665 - 1666), pp. 231-239Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/101499 .

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( 3 ) uNt, 14.

PHILOSOPHICAL T R ANS A C TI ONS.

Mnnday, Ju,ly 2. r666.

The Contents. fn Account of a New kindof Barofcope,which may be call'd Stati- cal ; and offome Advantages and Convenienter it hath above the Mercurial; communicated by Mr. Boyle. The Particular Obferva- tionf of the Planet Mars, frmerly intimated to have been made by Mr.Hook in February and March laJt. Sem: Obfervations,made in Italy,confirming the former;and n'itball fixing the Period of the faid Planet's kevolution Obfervations, lately made at London, of the Planet Jupiter: as al/b ofSaturn. A Relation of a fad £Ef fed of Thunder and Lightning. An Account offome Boo£k, lately publjb' ; videl. The Qelations of divers Curious eyages, by Alotf. Thcvenot: A Ditcourfe about the Caufe of the'Inundation of the Nile, by Monf. de la Chambre; hoth Frencl: De Princlpiis s qatiocinatione eGometrarum, Contra Faflum Proffjjorum Geo metria, by ir. Hobbes:IQng Salomons Pourtraiture of 'Old Ag, by J. Smith, M. D.

An Account Ofa New kind of Barofcope, which may be called Statical;

and of ome Advantages and Convniencies it hath above the Mercurial: Comrnunicated, ome while fince , by the Honoarable Robert Boyle.

f- S fr the 7lerv kiiid'ofBarofcopes, which, not long Ag6.dI int'rnatetd to you, that my *See Num.I .p.

gW ? [f hafte wofid'iiot permit me to give i 8. Pbil. Trafr- -;S^^ jN you an accoult off; fi nce yciur Let- atn-I

ters acquaint ine,that'you ftill defigu a Communicating to the 1 i Curious



(2 )

Cur'ous as much Informatio,a may be, in reference to ia. rofcpc;I fhall venture to feuid you fome Account of what I did but iname (in_ my forme'r Letter) to you.

Thiougoh by a Paffage, you may mleet with in the i9th anld 2zoth P~ages of my Thermometrical Experiments and Thougbts, youi may find., thlat I did fome years agoe thinik upon this New kinid of Barofcope-; yet the Chaniges of the Atmiofphier &s. Weighit not happening to be then flich, as I wifhi'd, anid being unwilling to

"e The "Scales here rneont deprive miy felf of all other ufe of the wer bfor cmptev Ee-exa6teft Ballance, *,, that I (or perhaps

witre befre cmpdetentrvm ay man) ever hiad, I confefs to you, made Aurn ~ that fucceffive avocations Put thi s at. xif(fil ijoith the thoufandib tempt for two or three years out of my

P,rOf 4Z4V thoughts ;till afterwards returninig to a pla ce,- w-here- I clhanc-d to fi"nd two or three pairs of Scales) I had left there) the fight of them brought it into my minid; and though I were theni unable to procure exa61ter ,yet my defire to miake the Experiment fome amenids for fo longt a negle6t, pu-t me u'pon confidering, that'if I provided a GlaJs-babe,m ore than ordiniary large 'and li,ght, eveni fuch Ballances, as thofe, mnight in fome'meafure performi, what I had tried with the Jfrangely nice onies above-mentioned.

I cau fed then ro be blown at the Flame of a Lamp fome Glafs.buble.s as large , thin and light, as 1 could then procure, and choo-fin,g amn hmcn,ta eemnd the, leaft unifit for mny turni, I counterpoifed it in a pai'r of Scales, that would loofe thleir X6 quiIi'brium with abouat the 3 oth part of a Grain,and were fiitfpenidea at a Frame. I placed both the Ballanice and the Frame by a good Barofeope, from whence I might learn the prefenit weight of the Atmofiphere. Tfhen Icaving thefe Inftru- ments together; though the Scales, being no nicer thanlIhave exprefs'd, were not able to ffiew me all the Variati'ons of the Air's weight,that appear'd in the Miercuri'al Barofcope,yet they di'd what I expe&ted., by fhe wing me variati'ons -no greater,than altte'rd the height of Qui'ckfilver half a quarter of an inch, and perhaps much fmialler,than thofe:Nor did I doubt,that,if I had had eithier tender Scales, or the means of fuipplying the Expe- riiaec'it with conVenlieDt accommodations, I fhbould have di.

fccrned



(23 3) fcerned far fmaller Alterations of the Weigglt of the Air,fi ice I had the plea fure to fee the Buble fometimes i'n an xjeUilibriz'&m; withi the counterpoife;5 fometimes, when the Atmofphere was high, preponde rate fo manif eftly, that the Scakes being gently fther the Cock would play altogether oni that fidle, at whichi

teBuble was hung J; aiid at other times (when the Air wa,s hea. vier) that, which was at the firft but the Co'unterpoife , woulid preponderate, and, upon the motion of the Ballance, make the Cock vibrate altogether an its fide. And this would con- tinue fometi'mes many dai'cs together, if the Ai'r fo lonig rc- tain'd the fame meafure of grv'y ;n then (uipon othier chani. gyes)the Buble would regain an aquilibrium,or a preponderance; To that I ha'd oftentimes the, fat isfa6tioln, by looking firft uponi the statical Barofcope (as for diftin6tions akeit may be calld) to f oretell, whte nteMruIl Barofcope the Liquor were high or low. Which Obfervations though they hold as well 'In Winter, and feveral ti mes in Summer (for I was often abfent d uri'ng that feafoni) as the Spring, yet the frequ.ency of their Vici'fl.it'udes ( whichi perhaps was but accidental) miade them more pleafant in thle latter of thefe feafonis.

So that,, the matter of Fa6thaving been made out by varietry of repeated Obfervat.ions, and by lometimes comparing feve'. rail of thofe new BarofcopEx to'gether, I fhall add fome of thofe Notes about'tliis Inftrumenr, which readily occur to miy me- miory,referving the reft till anothe'r opportunity.

And Firfi, if the grouind, 'on which I went in framing this Ea' rofleipe, be dema nded, the anfwer in fhort may be ; r. Thiat, thoughi thle Glafs-buible, and the4Glafs-couuterpoi'fe, at the time of their flrft bei'ng weighWd,be in the Air,wherein they bcvh are weigh'd, exa&Iy of the fame weight; yet they are nothi'ng near of the fame b'ulk;i the- Buble, by reafon of its capacious ,cavity C(W'hich co'ntains nothing but Air, or fomethintg that weighs le'fs than Air) bein-gpe'rhaps ahundred or two hundr-ed ti'mes (forlIhave not convdni'encyto meafure them) bigger than'the Metalline counterpoife. z. That accordi'ng to a Hydroftat'ical Law (whlich you know I hiave lately'had occaflion to make out) If two Bodies of equal gravi'ty, but unequal bulk come to ble weiggl'd iti another Mfedium, they will be nio longer

I i 2. cqui-



(234) equiponide-rant; but if the new mediu m be heavier, the greater J3dy abenliheinSee,will loofe, more of its weighit,

thanl the leffer. and more compa6t;- buit if the~ new M/kedium be lighter thani the firft, thec.n the biggyer Body will outweighi thle leWfer: Anid this difparity, arifinig from the change of Medium's, will be fo mutch thle greater, by how nmtch the greater jinequality of bulk there is betwveen the Bodies formerly equiponderant. 3. Thiat, laying' thiefe two togrethier, I confiderld., that 'twould

be al o., as to the effe6lt o be produiced, whiethr th o dies were weighed int Mledium's of differin'.g grav,ity, or in the fame -IMedium, in c'afe its (/1pecifick) gravity were confiderably alter'd:- And confeque12nty, that finice it appear'd by the Ba.6 rofcopte, that thne weight of.the Air was fomietimes heavier, and fc*netirn es lighter, the alterations of it, in p oint of -gravity, from the weighit, i't was off at -flrft couinterpoifiig of the Buble of i't, would uneqjually affe6t fo large and hollow a Body,as the Buble, and fo fmall antd denfe a onie, u~s a Metallin weight:- And wvhenl the Ai'r by ani increafe of gravity fhould become a heavier ,Akldium, than before, it would buoy uip the, Glafs more than the (C.ounterpoife ; and if it grew lighter, than it. was at firft,

wuld fuffer the former to prepondert:(h lutain and Proof 'Can fcarce be added in few words ; but, i-f it be dle. fired, I may, God permitting, fend you them at my next leafure: ) And though our Englifli Air be abouit a thoufalnd tim'es lighter, than water, the difference in weight of fo little Air, as i; but equal it] bulk to a Buible, fe ema'd to0 give fmall hopes, 'that it would, be felirible upon a Ballanice; yet, by making the Buible very large anid light, I fuppofed and found the Evenit, I have already related.

Secondly, The hermeti'cally feald'dGlafs.-bnble, IL employed,, was of t'he bi'gne1s of a fomewhat lar'ge Oranige, and wei'gh'd abouit r. drachme and Io.grains, But I thought it very poffible, ifil. had been better furnifh't wi'th conveniencies (wherein I af. terwa-rds found, I was not miftaken ) to make- ( among- m anIy, tlhat -mighit be expected to mnifcarry) fo m.e,that might be preferable to this, either for capacity or lightnes, or both;- efpe. cially if care be taken., that they be not feal'd uip, whilit the'y are toolhot. For3'though loie would think, that it were advan.

tagious



(23 5) tagious to rarify and drive out the Air as much as is poffible,bc. caufe in fuch feald Bubles the Air it felf( as I have elfewhere fhewn) has a weight; yet this advantage countervails not the inconvenience of being obliged to increafe the weight of the Glafs which when it includes highly rarified Air,if it be not

fomewhat l¾rong,vill be broken by the prelffre oftheExternal Air, as I have fufficiently tryed.

Tbirdly, I would have tryed,whether tlhe Erynej/ and Aloifl. wre of the Air would in any meaftire have alter'd th3 weighi of the Btble, as well as the Variation of Gravity produced in the

Atmolphere by other caufes; but the extraordinarily confallt ab-

fence of Fogs, kept me from making Obfervations of this kind; fave that oie morning early, bcitng told ofa miff, I feit to fee (being my felfin bed ) whether.i:t made the Air to heavy as to buoy up the Buble; but did not learn, that that mift 'had

any fenfible operation on it. Fourthly, By reafon of the difficulties and cafualtics, that may

happen about the procuring and preferving fulch large and ligllh Bubles, as 1 have been lately mlentioning; it may in foimd cafes

prove a corievenience to bhe inform'd' That I have foinetimes, inftead of one fufliciently large Butble, made ufe oftwo, tliat

were finaller. And, thougl a fingle Bible of competent big- nes be much preferable, by reafoin. tlhat a far lefs quantity alnd weight of Glafs is requifite to c.onpr'if.4ien eqialtcapacity, when the Glafs is blown into a fingle IBuble d}an whef- it is divided

into two; yet I found, tlat the iemploying ofi tw6 'inflead of

one, did not fo ill anfwer my exfpeCtations, but that they may for a need ferve the turn inftead of.tlie other; thian which

they are more eafier to be procutreld: And: r the. Ballance be

ftrongenoug h to bear fotuch. Glafs, withou-t being:injur'd: by employing two or a greater number of large Bubles the ef- fe6t may be more confpicuouss than if only a fingle Buble

(though.a very good one) were employed. This inftrumentmay be euclh impr:oved by divers Accom.

modations. As FirJf, There may be fitted to the Anfa .( or Checks of the

Ballance ) an Arch (of a Circle ):'divided into r y. or 20. (dg. ( more or lefs, according to the goodnefs of the .Ballance) that

the Cock refting. over. againflt. thife DiVifions , may readily. and



(s36) and without Calculatton ffiew the quanti'ty of the Angle, by whiich, when the fcales propend either way, the Cock declines from the Perpendicular, and the beam fromiits Horizontal) pa- rallel ifm.

Secondly, Thofe, that will be fo curious, may,inuftead of the ordinary Counterpoife (of Brafs) employ one of Gold., or at Ieaft of Lead, whereof the latter being of equal weight with lBrafs, is miuch lefs in Bulk, and the former amounits not to half its big,(ncfs. emaeo

Th,irdly, Thefe parts of the Ballance, that may b aeo Copper or Brafs, without any prejudice to the exa9knefs, will, by being made of onae of thofe Mettals, bc lefs fubje6t, than Steel, (whi'ch yet, if well hard ned anid polifh'd, may laft good a great whille) to mru with long ftandinig.

Four.thly, Juiftead ofthe fcales, the Buble may be hung at onec cnd of the Beam), and only a Counterpoife to it at thc other,thac the Beam may not be burthen'd withi unncceffary weight.

Fiftbly, The whole inftrument, if placed in a fmall Frame, Ilik-. a fquiare Lanithorn withi Glafs-winidows, and a hole at the top for the Commerce of the initernial anid external Air, will be miorc free from duft, arid irreguilar agitations;* to the latter of whlich, it will othierwife be fometimes incidenit.

Sixvtbly, This inifrumnent being accommodated withi a light Whecele and an Index ( fuch as have been applyed by the excel. lent Dr. (Chr.' Wren to open Weathier glaffes, anid by the CinDge- niouis Mr. Ho4kto Barofco.pe.r) may be made to fhiew muchi more, miniute variationis, than otherwife.

Seventbly;3 Anid the lengthi of the Beam, and exquifi-nefs of the Ballaiice, may eafily, mtii but any of the foregoing helps (and muchi more'v-itb them) make the iniftriarnent far exa6ter, than aniy of thofe,- I was reduced to employ And to thefe Accommodationis divers others m-ay be-- fiiggefi ed by a farthe-r =or4deration of the - nature bf the'thingr, and a loniger pra6ti ce.

ough i-n fomnerefpedts this static-a/)Baro'fcope be iniferior to the- Mrcuri'al;- yet in others it has its own. advantages anid conlveniencies above it.

And rb, It confirms ad ocuZmm our former Do6lrine, that the fallinig and rifing of the Mercury depends upon the varyinig weight of the Atrnofpbere i fince in this Barofeope it cannot

b I..



('.37) be pretended, that a Fuga vacui, or a Fzunicu?ufr, is the caufe of the chaniges, we obferve. .2. It fihews, that not onily the Air has. weight., but a more conifiderable one, than fome Learned mien, who will allow me to have Pro% I'd it hias fome weight, will1 admit ; fince evena the variation of wegh infmlaqatt of Air, as is but equal in buIlk to ani Orange, is manifeftly dii-f coverable uponi fuch Ballances, as are nione of the ni;ceft. -3.Thi5 Statical Barofcope wil'l oftentim'ies bc more parable,. thani the other : For many will finide it more eafie,to procuire, a grood

pair of Gold-fcales, anid a Buble or two,. than a longC Canie feal'd, a quantity of Qgk/le,and all the other requifits. of the Mer'curialBarofcope; efpecial-ly if we comprife the trouble and skill, that is requifite to free the deferted part of the Tub,-. from Air- 4; Ad whiereas the difli'cu!ty of remnoviing the~ Mer- cuirial lnitrument has kept men from lo much as attempting to do it, even toxieighbouring places ; the Effential parts or thle Scale-Barofcope (for the Fram-e is none of themi)- may very eafily in a little roomi- be. carried, whither on'e will, withiout thle hazard of being fpoil'd or injutr-d. 5. There is niot in Staticlal Barofcopes, as in the othver, a daniger of uncertainty , as to the goodnefs of the Thftrniments, by reafoni, that in thejethe .Ai;ris,- in fome more, and in fomne lefs perfeatly excluded;i whereas in. thofe, that conifideratioii hcas no place. (And by the way,I have fometimes, upon this account , bleen able to di'fcovcr by ouir new Ba ro fco pe, thia t a n e ftee in'd Mfercurial on e,to whliichi I C oim pared it,was not wcll freed from Air.) 6. It being,aa I former. ly initimated, very poffible to difcover Hydrofla tically, bohte bignefs of the. Buble, anid the Conitents of the cavity, and the weight and dimenfions of the Glaffie fubftance ( which together with the included Air make up the BLuble) muatch l y difcover'd by this Inftrumenr, as to thIegto the

t Ai,be~

lute or refpeRive. For,when the Q:cJlvri heMrura a rofcopc is cither very high, or 'Very low , or at a middle ft.aid'il between'its greateft and leaft height, bringiog the Scalt-Baro-' meter to ani Exact £quili~~ri~mm 5 ( with very minuite dIvfos of' a Graine, ) you may, by watchfully ob(erving,s wheni then .Mercury is rifen or falnjuift an inch., or a fourth, or hialf ani inch c&c. anld pattiig in the li'ke minUte diviflons -of a Grain to the lighter Scale, till. you have again- brought the Bal'lancee to nn

cx qu i5tra



(2 3) exquifit/Equilibrium ; you may, I fay, determine, What known weight in the Statical Barofcope anfwers fuch determinate Al titudes of the afcending and defcending Quick°filver in the Mercurial. And if the Ballance be accommodated with a divided Arch, or a Wheel and Index, thefe Obfervationswill affilt you for the future to determine readily, by feeing the inclination of the Cock or the degree mark'd by theIndex,what pollency the Buble hath, by the change of the Atmopiheres weight, acquired or loft. Some Obfervations of this nature I watchfully made, fometimes putting in a 6?th fometimes a

2h fotIoetimes a I 6t'. and fometimes heavier oarts of a Grain, to the lighter Scale. But one,that knew not, for what ufes thofe little papers were, coming to a window, where my Barofcopes flood , fo unluckily fhook them out of the Scales, and con. founded them, that he robb'd me of the opportunity of making the nice Obfervations I intended, though I had the fatif- taction of feeing, that they were to be made. 7. By this Sta- t al Inftrument we may be affifted to comoare the Mercurial Barofcopes of fveral places (though never fo difantt) and to make fome Eftimates of the Gravities of the Air therein. As if, for inftance, I have found by Obfervation, that the Buble, I employ, (and one may have divers Bubles of fevcral fi es, that the on'e may repaire any mifchance, that may happen to another) weigh'd juft a Drachme , ,when the Mfercuria Cylinder was at the height of 295 inches ( which in fome places I have found a niodratej altitude;) and that the Addition of the 156th part of a gr. is requifite to keep the Buble in an A1,qiltritum, when the Mercury is rifen an gth, or any determinate 'part of an inch above the former fation : When I come to anoth'e place, where there is a Mercurial Barometer, as well freed from Air as mine (for that muft be fuppofed ) if taking out my scac i;- ftrument, it appeare to weigh precifelv a Drachme,. and th:e Mercuryin the Barofcope there ftand atjuft '29. indies3 we may conclude the Gravity of the Atmofphere-not to be fetnfibiy unequal in both thofe two places, though verydiftant. And though there be no Barofcope there, yet if there be a an ddiri- onal weight, as for inftance, the i6th part ofa Grain requifite to be added to the Buble, to bring thefcales to an'/Equiltbritm, ir will appear that the Air at this fccoid place is ncathat timed

fo



(23 9) fo much heavier, than the Air of the former place wat, when the Mercury ftood at 292 inches.

But in making fuch comparifons, we muft not forget to con- fider the Situation of the feveral places, if we mean to make Eftimates not only of the weight of the Atmofphere,but of the weight and denfity oftcheAir.For,though the Scales wil fhew(as has been faid) whether there be a dififrence of weight in the Atmofphere at the two places; yet, if one ofthem be in a Vale or bottom, and the other on the top or fome elevated part of a Hill, it is not to be exfpe(6ed, that the Atmofphere, in this latter place, lfhould gravitate as much,as the Atmofphere in the former, on which a longer Pillar of Air does lean or weigh.

And the mention, I have made of the differing Situation of Places, puts me in mindoffomething, that may provea- nother ufe of our StaticaBarofcope, and which I had thoughts of making tryal of, but was Accidentally hindred from the opportunity of doing it. Namely, that by exa&ty poyfing the Buble at th: foot of a high Steeple or Hill, and carryi.g it inl its clofe Frame to the top, one may, by the weight requiite to be added to Councerpoife there to bring the Beam to its Hori- zontal pofition, obferve the difference of the weight of the Air at the bottom, and at the top 3 and, in cafe the Hill be high enough, at fome intermediate Stations. But how far this may affiftl en, to cflimate the Abfolute or Comparative height of Mountains, and other elevated Places; and what other Lfes the Itnftrumcnt may be put to, when it is duily improved ; and the Cautions, that may be requifrie in the'feveral cafes, that {iall be propofcd, I muft leave to more leafure, and'farther Conlideration.

The Particulars. Oftbofe Obfervations of the P,anet Mars, Jormerly intimated

to have been made at London in the Months ofFebruary and,March A. i 66j.

To perform, whlt was promifed Nrmn. xi. of thefe Papers, pag. x98; 'tis thought nt now to publifl the Particular Obfer- vations, concerning the fpots in Mars, and their motiot,as they were made with a -3 foot Telefcope, and produced in

K k writing

(23 9) fo much heavier, than the Air of the former place wat, when the Mercury ftood at 292 inches.

But in making fuch comparifons, we muft not forget to con- fider the Situation of the feveral places, if we mean to make Eftimates not only of the weight of the Atmofphere,but of the weight and denfity oftcheAir.For,though the Scales wil fhew(as has been faid) whether there be a dififrence of weight in the Atmofphere at the two places; yet, if one ofthem be in a Vale or bottom, and the other on the top or fome elevated part of a Hill, it is not to be exfpe(6ed, that the Atmofphere, in this latter place, lfhould gravitate as much,as the Atmofphere in the former, on which a longer Pillar of Air does lean or weigh.

And the mention, I have made of the differing Situation of Places, puts me in mindoffomething, that may provea- nother ufe of our StaticaBarofcope, and which I had thoughts of making tryal of, but was Accidentally hindred from the opportunity of doing it. Namely, that by exa&ty poyfing the Buble at th: foot of a high Steeple or Hill, and carryi.g it inl its clofe Frame to the top, one may, by the weight requiite to be added to Councerpoife there to bring the Beam to its Hori- zontal pofition, obferve the difference of the weight of the Air at the bottom, and at the top 3 and, in cafe the Hill be high enough, at fome intermediate Stations. But how far this may affiftl en, to cflimate the Abfolute or Comparative height of Mountains, and other elevated Places; and what other Lfes the Itnftrumcnt may be put to, when it is duily improved ; and the Cautions, that may be requifrie in the'feveral cafes, that {iall be propofcd, I muft leave to more leafure, and'farther Conlideration.

The Particulars. Oftbofe Obfervations of the P,anet Mars, Jormerly intimated

to have been made at London in the Months ofFebruary and,March A. i 66j.

To perform, whlt was promifed Nrmn. xi. of thefe Papers, pag. x98; 'tis thought nt now to publifl the Particular Obfer- vations, concerning the fpots in Mars, and their motiot,as they were made with a -3 foot Telefcope, and produced in

K k writing



an account of a new kind of baroscope, which may be called statical; and of some advantages and...

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