장음표시 사용
271쪽
hon occupio in examining the salineas and tho current os the soas round the coasi os Scandinaria Prematae certain circumstances, hichappeare to offer a ne an clear explanation os the origin os some os in ocean-currenta, os hic prerious explanations ha been attemptΘd, groundo on assume di rences in the ea-Water' specific gravit ').Τhis led me to a more extensive examination os in causes, hic in generalisive is to stream in the ea, an have published an essu
resulta os that or in a moro systemati form and a the fame time, to enter omeWhat more suli into certain potnis, hic in that orkhavo oon ut incidentali touchedispon. ΕVen he we leave ut os consideration the possibilit of ocsaniostreanis sin produce is xuatelluri attraction, there are, it sano , many causes, hic ive is to motion in the ocean's ater gain ortos of heat, ain QVaporation, reeging, Variation Os atmospherio pressure, Winds etc., are cause of this indoiat arising directi or indirectly homunequa distribution os in sola heat. M therasarns men, Who have made in problem os in origin os in oceani current a subject os sindy, have pia more or leus attention to ali ines causes, though osteni a ne-side manner so that an almos exclusive importanc hau bsonattributo somstims to ne an somelimes o noster. Since ho everthe fac is that almost very one os inose causes has a someWhat important influenc oti the movement os the wator in ome specia district
y I publishe a hor ossa on his subject in the Archive de sciences de laBibliothhque Universelle, Sept. 1875, entilled Notice surrae mouvementa de rea de me dans tu volsinage de embouchure de fleuves.
272쪽
2 F. L. ΕΚΜΑΝ, O the ocean, and ver motion in ne par mustinive is to motion in Other paris, Ver ocean-current stricti speahing depend on many uch causes. he usines of the hydrographor hould thorosor be atho todiscovo what part ach of them has in in sormation os tho sparate streams, than to care out an particula theory rounded po any specia causo. quantitative determination of this in can howoverint present ni be placed amon thino to e Wished sor, a the amount os observations necessar sor iis fir ing ut, oes no as et exist, and the calculation os the effect moreove presuppose both tho number aridnatur os the cooperatin cause accuratel knoWn. he opposite vie siliat venis to the present time are entertaine on his subjeci, eemto indicate that the preparation os the question is not et sussicientlyadvanoed, and it is the object of the present or to contributo in omemeans to the supplyin os his deficiency. For ur purpos I divido the bove mentione cause into two groups, amel A such a produce a change in the water' lene and thus indirecti sive is to streanis and B me a immediately produce a stream in consequence of the mechanica action, hic a medium ali eady in moltimeteresse on the water. o his ast catego , Whicli must itfel also produco a change os levet bolong indu and the mucos rivors surthor- more Ver ocean-current, hoWeve it ma haVe originaled immediato becomos iiset suci a cause. o the omer categor belong specialty
Τhe orna os a pheroide os revolution, hicli in sursace of the oceaD ould ther se assumo, is subjectrio mali perturbations. In addition to tho oriodica disturbanos produce by tho ooΝ' attraction, ehave in tho rs place that, hici resulis homolis nequa distributionos the atmospheric presRure Accordin to the mean arometri pressuro in tho nolobourhood os in Atlanti in the ortherii hemisphere, as determinod by ScΗou and OGGENDORPF, and the barometerobservations in the solitherii hemisphore, collected by AURY the surtace of the oceano the equator appears to staud about 11 contishtros hictor hanat the tropiosi in consequenco of the diminishing of tho baromotric
273쪽
than at tho tropios. I the differsnce in the atmospheric pressure ereabsolutoly constant, his ditareno os leve could notisive is to any Ηtream, ut the water-partiole of the incline sursaces ould movo withoqua facilit in an direction Ont When, rom Rome ther cause, thewater stream ho on latitude to another, a the dissereno os homea barometri pressure have a modisyin influenc on the motion sine stream. The troams, that o froin the tropic toWard the potes, will avo their movomen very lighti facilitated those ominii thoopposito diroction ill e retarded, ut accelerate again a Boon asine have passe the tropicB. Εver variatio of the atmospheric pressure must cause ater totio homone placeo another; ut these hanges, being oni occasionaland of hori continuance, an me ni a triuin effect upo the real Oceani currenis, although the may have a more considerable tempora influenco D the stream in stratis, hic unite separate oceani basinswith achother. Τho changes os levet, caused by eat an cold evaporation andraintail, o the ther hand ma givo ris to constant movement in thoesea-Water for these operate illi an verage constant disserenosis foroso difforon portions os in ocean. I me iready said that the cause Atream in consequenc os changes in the leve of the ea. ho howeve also alter the volum an specific gravit of the ea ater, tholaiter parti by changiniit salines an parti it temperature. Each os hos changes has it effect upo the Ocean' circulation, an cannot conside itis a marier os indifference, hethe we assume One or the ther of tho as in immediat cause of tho rosultingutream. AURY, and many thors after im, have oinred ut a thooause tho Variation os the specific gravit os the se mater. When soroxample lis in tho h ter: The origin os Currenis epitomiges hi vioWos the subject, s usos in following ords ' eIs we xcopi tho idos and the partia current of the ea suci a those hich may be created by the Wind we may lay own a a rute, that ali in curesnts of the ocean we thoi origin to dissereno os specific gravit bet se Aea-wnter at ne place and Θa-Water at another sor hereve there is sucha difforonos, it is a dissorencs that disturbs quilibrium an cur-
274쪽
4 F. L. ΕΚΜΑΝ, renis are the consequence. The hearier ater me to aes the si te and thera Mor honos ino savior comos sor Wo fluida dissering in p. gravity, and standiu at in sam levet, an no more balanco each other than nequa we his in the opposito scales os a truo balance. W see that accordin to this How in fidit impulae to tho troam arises romthe earier ater, hich, as standiti a the nam love a the lioter, in consequenc os tu greater eight displaces the alter in tho deoperstrata. In his manne ΜΑuo endemoum to exples in unde current
in stratis, hic unite oceani basin os different degrees os saliness, and this explanation is coopte by CARPENTER and thera. I foems to me, that this explanation os in unde current, hichhas moreove been extensivel applied to stream in tho operi ocean, to impliciti repones on the common notion of tho fixo lovo of the ocean's ursace, and that tho soli oming theorems, hoW-er simple, deserveespecta attention in s much a that the must e tho soundation os a
correct comprehension os the phoenomenon.
1:o Whon in equilibrium etWoe two masses of mater has been disturbed, Wo cases are possibie, namel Howhon the equilibrium is disturbe throughout at the strata down to tho ouom and b), whon theo ludibrium is disturbo oni to a certain depin belo the sursacΘ. hefim caue appens, hen the specific gravit in both masses is in fame, but tho levo difforent, or in leve the amo, ut the sp grari , ut leastin the uppe strata, disserent. The alter case presuppones that in specific Wsio in both masses is in the lower strata tho amo, ut different in tho strata siluato above a certain levia, and moroove that thethichnos os these latior strata is inverset a thei specific gravities. 2:6 Botwoen two strata os Water of tho sanas lovo an depth, butos disseront specific gravi , there illae a dissereno os prossure, hicli atine surtaco i, ut incroases illi the depin bolow in sursaco. Shouldhowevor the lighter ater e so much aisod that tho dissereno os pressure at it greates depi Vanishea, then at an potnt bove thaldopth tho toler ater Wil produce a greator pressure than in hearier, and tho differsnc increme a We approach the sursaco; ut in sum ostiis dis ronces os prossur of the wo strata ill bo os in tho atterpositio than in the former. 3:o Whon in equilibrium stwoe two masses of wator is distu bed, tho motion os the particis mill e nuchis to rostor the equilibrium at tho lsast possibi expens os time an action. Foro invendissereno os pressure the require motion ill occup more time, hen
275쪽
the differetice os pressure ni extenda to a certain depin than hen itextonds to the bottom an in genera a greater time is required, henino disserenos os pressure extend to a les depili, than when to a greater. From hos theorems, tho truth of hic Ι nee no sto to demonstrate, I inal no endemou to dra Rome genera concluSions respecting the effeci, hic diffsreuces os specific gravit bet est thowater in different paris os in ocean an me o the origin os oceanic
Is w dsfine the norma se leve as that which would result homilis orce of gravit and the artha rotation illi the mean barometrio pressure, certain deviation froni that levo must tali place in consoqueno os different specific gravit in disserent paris of the ocean, and thos deviations ought to approximato to, ut o suli reach those, whio would bo stermine by the invorse ratio of the p. rarities os
Lotis firs suppos the case of the water in a corini partis theocsan siniti ter than the est down to a distance, , elo the sur- tace, ut that tho ursace iself A verywhere normal. Wo differsnthind of motion Ouid immediatet be producod. he ioter ater would bo isto by the surroundinchoavier, ill the dissereno os pressuro ut the ne leve os ita lower fide, n , anished, ut ascit pressureat ali levet above n havo o become greator than that os the hemior ater, it ould instanti belli to displace an ovorflow in latior. his movement os in lighter ater ould howeve require considerabi more timo than the movement of the heavier ater, hereb the lighter Wastino an continuos o o linod a iis levo sinks by latora diffusion. For in sum os the dissorsnces os pressure, hic caused the elevationos in ii ter ater, ero in the rs place greater, than the sum os thedisserenoes that causod iis diffusion Oward the uides. Secondi thodisserenoes os pressure, hicli caused the rst motion, must exten allthe way to the ouom, herea those, hic cause the lalter, extera nodoopor than in lighter stratum iiseis, an even illiin the extent os that avo thoi chios stac confino to tho superficia strata. illi rogar to the velocit os these motions that os in heavier ator ill borolativel liuio sonsibio, ecause it ahes place in a sectio os largor area, ut tho motion os inscii ter ater Will o seen to forma more rapi an more clearly defined Atream.
Some important exceptions os this ast statement ill bo hereaster noticod.
276쪽
6 F. L. ΕΚΜΑΝ, Τlis mos immediat an essentia consequenc os suo differetices os specific gravit bet eoi different paris of tho ocean is the disser-ees of evel, hic differetices howeve subsequently ive is to Superficia streams, hereis the lighter trier displace the eavier. y these StreamS, in consequetice of the malines os insis oction, tho distur doquilibrium an only be restore Hlowly, and thei continuanc ma in resore e considerable both a rogard time an extent. Is the causes, whicli produce the change os specific gravit operate in a constant man-ner both hs differetices os love and the consequent troam Will e
Whon in squilibrium os a mas os maior is disturbe by causes, whicli do no alter, or at eas do no diministi the water' specific gravity the disturbane must extendisti the way to the otioni, and the difforences os pressuro at ali depin beneatholis lowos love os in Hii saco ill e qual. he equilibrium is then restored by a genera mo-Venient os the whole maus, hic Wili howsvor o lis os visibis in proportio a the mas os ater et in motion is greater We have hero an essentia cause os the dissereno in th strenni os the troamsobsorve in sal an hos Water. For os ali the causes hicli an produce stream in the lauer, thoro is ut ne, hic can sensibi affect the water' specific eight Viκ Variations os temperature. The p. grarit os Hea-Water On the contra , bosides ein much more offecto by Variations os temperature, is stili further affecto by tho descent os hoshWater pon iis ursaco. ven is the whole basi os the coan ero filio Mili hos wator and that water exposed to the Ost extrem meteorological influencos, hic the different tracta os the earin prosent, theiaceste sup0rficia stream produce Would not be early qua sither inpoWe or extent to those e no observe in the water of the ocean '. We procee no to examine separalel Hach of the causes, hichten to produce hange in the specific gravit os Hea-Water, illi a VieWto ascertaining thei influenco on the water' motion, and sor simpliciW's Sahe we tippo8e mly one of the3 cau8ecto operate at a time. e have firΗt:
' Although the importance of specific gravity, as affecting the stream in Deshani sal mater has atready been caresuli potnted ut by Α Y, I have neverthelessthought it est here o ouch upo that subjeci, eoaus it oes no appea to methat ho has adduced the causo os the phoenoniena in question, hic I look upon sthe clites.
277쪽
V, sor a moment suppos the ater os the whol oceani thesam temperature, ut stat an extenRive portion Os the surtaco hasciust been exposed to the influence of the ola heat, the water in that localit would expand an iis levo Would e alsed. ho no lsvel maybo supposed suci a that required by the specific gravit os the warmod str tum, ithout an laterat motionis the Warmer Water haring been necessa . But a tho ovo was alse and the disserenoe os pressure in tho upperstrata increased the wam mater Would presently bein to Atream oumardS. Ita lovo would thus again in and the the water' rise, hereb theoquilibrium ould bo disturbe down to tho bouom, and the consequenoewould bo that tho wator rom elow ould o to the warme placetii tho quilibrium hould e restored. Is tho ouros of heat, stat produce in change, ceased O aut, both tho bovo describe motions the surtae stream and under-Stream, would continuo though it continuali decreasin velocit on accountos the continuali docre ing diffsronoe os pressure, tantii ali strata ostho fame eight attaine the fame temperature, and the Bursace Recor- dirigi become everretiere normal. Is o the ther hand the ource os hea continue to operate it constant poWer, the water arrisin hombolo Would in iis turn o arme and thus the motionae perpetuated. In proportio a the warmo mater recede honi the warm localit intho sor os a superficia stream, it ould pari Wit iis sat an atra tauch an quilibrium ould bo est lisbed Θtwee at the circumstances, that cauae the wo streams, that in quantit os maior, brono in unit is timo by tho under-stream, ould bo qua to hat was carriedo by the sursace-stroam. What position Ouid the warnier ater inhemith respecto the older, hen his stat of thing came to passyIt is olear, stat, is tho tW water-sursaces are at the Same leVel, there an sis dissereno os pressure to et the sursace-stream in motion, and again is the warme stratum assumo the position determine byiis specific gravit ouly there ould bo no rivinisorce to produc ineunder-stream. he positionis the warme stratum must theresore lis bemeenthes extremes it must e such, that both strata re ut throuo is animaginar sursace, bovo hic the differetice os pressure cause an ut Ward-flowin stream os arm Wator an beneat it at unde stream scold. Is in proportions ore such, that in volumes os mater, hichtho tW aueam carrie onWard in tho uni os time had soctions os squal
278쪽
ars to move through, th differetices os pressure, hic drove the su sace-stream, ould require to ut equa to thous, hic drovo hounder-current, O the position os the warm stratum ould bo about in thomiddis belwoen the extremes above mentioned But, a the cane reatly is in the ocean, the ectio os the sursace-stream is sarcies tha that os thounder-stream, an accordingly the disserenos os prossure, hic drivo the superficia current, must be Ver considerabi greater tha those, Whioli set in motion the unde current. O in ther orda The positionos the warm tratum must e much marer to that, hic ita veris gravi rei id assigno iit, than to the ther extreme. Her no alio anco has been mado so the changs in the position os the strata, hic ma ariae homtho vis viva os the stream produced. Is tho water at tho ursace os the ocean is coole to a lomertemperatur than the subjacent strata, the water at the sursace ecomes heavior, an supposing the salines of the lower strata notrio boareater,it must, lihe very the hearier ody, sin towarda tho ouom. Is thocoolin ove the whole localit be uniform an constant, there illis sultis vortica circulation, hic Wil continus illisl in Wator has o ched in fame temperature. Is o the ther an oni a portionis inosursace is exposed to coolin influenco rom bovo, in leve os that portion ill in bolo that os the res and there ill rescit an externalstroam toward the chille place, arising rom the greator hydrostatic pressure of the surroundin Warmer ater. But in hi case thoro arisos a the fame time a ne current, independent of the changs os lovor sortho hille mater, in consequelice scit increme specific gravity, inlis, displacos hs ater hic preriousi forme the ouom-strata an diffuse itsol unde thsm. heso motions is the wator in tho uchillod localit were unable to receive eat, ould continuo though with lossan los ustocity untii the hole in s os mater had sache tho temperatur os in chilis placo. Τho change os Volume, hic the superficiat wator undergoΘΗsrom esse or lowere temperatur are howeve accompanio by the sollowin phoenomena. When the superficia mater is anmhere armed, it dilatation in horizonta dimension experiences a resistanc hominΘaloining strata, the effect os,hic must e to causo tho his dilatation to b in the vortical direction; his increa os in differsnces of pressure, hic give se to superficia current, hil in rosistanc toth advancin unde current is diminished. An vico versa, he t sursaco is cooled iis horizontal contractio is accolorated by the pressuro
279쪽
tractio in tho vertica diroctio is diminishod, and accordini tho disso-
rences os pressure, that cause in unde current, exaggerated.
The offoci thon, that the arth's arminii the eighbourhoodos the quator an coolin in that os in potes ould avo pon hoposition an motion os the strata in the ocean is there ere no thermodi yin circumstances, ould e the solio 1ag: h lovo os ins sawould bo hango by risin a in equator an sinhin at the potes Τho oviations roni the norma levet, hich ould thus arise, ould in Rome measure approximate to those, hich accordin to the laws osoquilibrium in communicatin tubes, ould e calculute to tali placo, supposing the ater specific eight a disserent deptiis to b accuratolyknown. Wo superficia current os arm atsi Wouldiso hom insequator toWard the potes, and wo les rapi under-current os oldwator in the opposito direction. At thes stream Would diffuso hom-selvos uniformel ove the hole readth of the ocean, With ni such modifications as ould aris froni the formos in continent and the rotation os the arth. here ould in hort be a circulatio estistiano is differsnc os temperatur attines, in iis nature somethin similar o what D: CARPENTER has described, though in iis causes different..Τho groat effeci, that the coolin os in ocean's ursace has uponine tomperatur of the deeper aters has been fuit devolops by D:r CARPENTER andes have heresore baroly ouchedispo it do notinowsve consider, that in account he has HVen O the oceani circulation, arising rom variation os temperaturo ), agrees With hates have bove dosorib0d. Is I rightly understan him, e suppose in ocean-sursaceat tho polos to e o a levet it that at in equator. In bis aso apilla os ater at tho potes, extendin to a certain spin bolo thosiarsaco, ould exert a considerabi Menter pressure han a corresponding one at in equator on account os in formers greater specificur
vlty and this differetice of pressuro ought, coordin to D: CARPENTER, to bo tho rivinisorce, that elevates the ater at the equator. hodriving orco producing the circulatio lies, accordin to his vis , notin W. B. CARPENTER O the Lates Scientific Reaearches in the editerranean, Procoed os R. Inst. o G. r. l Marcii 187I; Ocean circulation3 Contemporaneous Remie , Sept. 875.
280쪽
10 F. L. ΕΚΜΑΝ, so much in the warmin os the water at in equator a in iis coolingat in potes. ho arm ursace current is ot rivon sorWard by aenis a tergos, ut by a vis a fronteo, amel by tho suctio that arises Domino inhing of the old potar ater On ali these potnis, I, a thereador ill Hready have discovered, entertain a disserent opinion. hooeat surptus os pressure at the potes anishes illi tho uniformit os
cordin to thoi specific gravity. he arm externa stream is reatlydriveti by a vis a tergos, hic exist at Ver poliat oscit course, in consequenoe amet of the disserences os pressure, arising hom tho highorlovo os in lightor ater eliind, herob the equilibrium is very heroin thooppo strata disturbe to a certain depth. he coid under-current would aris hom another simila cause, amely the disserenoe os pressure, caused by constant filii os the superficiat ater in armor latitudo an amu in colder, hereb in equilibrium etween tho water- strata ould e constanti disturbe doWn to the ouom Lasti no servo that the oceani circulation, hich could botrought about by disso- rencos os temperatur Only, Ouid e sarcies powersu than, an os acharactor holi different hom that, hicli alie actuat phoenomon os inoocean present, ecause ther entiret dissimilar and Ver powersul causos contributo to thei production, os,hicli more heroaster. Chillin os ater o a certain degre produces Deeging. Is me calculato hat change in Volume of Sea-Water undergoo in cooling, sotha puro ater is separate hom it in the formos re movin ico ),wo id that in last resus mill e a mali diminutio os volume, and
that coordingi Water must flo from omeWhere or the to the spol, whors in hooginiis Oing n. The formation os ico heresoro causes no intorruption os the effeci, hicli the coolin ca produco on the motion os the ater.
3 Accordin t m experiments the maximum densit and Doezing oint of sea-water When not Verchille an a the sua barometri pressure tali place atthe ollowin temperatures: