10 March 1967, Volume 155, Number 3767

The Historical Roots o:Our Ecologic Crisi

Lynn White, Ji

A conversation with Aldous Huxleynot infrequently put one at the receiv-ing end of an unforgettable monologue.About a year before his lamenteddeath he was discoursing on a favoritetopic: Man's unnatural treatment of na-ture and its sad results. To illustratehis point he told how, during the pre-vious summer, he had returned to alittle valley in England where he hadspent many happy months as a child.Once it had been composed of delight-ful grassy gl-ades; now it was becom-ing overgrown with unsightly brushbecause the rabbits that formerly keptsuch growth under control had largelysuccumbed to a disease, myxomatosis,that was deliberately introduced by thelocal farmers to reduce the rabbits'destruction of crops. Being somethingof a Philistine, I could be silent nolonger, even in the interests of greatrhetoric. I interrupted to point out thatthe rabbit itself had been brought asa -domestic animal to England in 1176,presumably to improve the protein dietof the peasantry.

All forms of life modify their con-texts. The most spectacular and benigninstance is doubtless the ooral polyp.By serving its own ends, it has createda vast undersea world favorable tothousands of other kinds of animalsand plants. Ever since man became anumerous species he has affected hisenvironment notably. The hypothesisthat his fire-drive method of huntingcreated the world's great grasslands and

The author is professor of history at the Uni-versity of California, Los Angeles. This is thetext of a lecture delivered 26 December 1966 atthe Washington meeting of the AAAS.

10 MARCH 1967

helped to exterminatemammals of the Pleisimuch of the globe is plaproved. For 6 millenniabanks of the lower Nila human artifact rathcswampy African jungle ;apart from man, wouldit. The Aswan Dam, flsquare miles, is only thein a long process. In r

terracing or irrigation, ov

cutting of forests by Ronships to fight Carthaginiarsaders to solve the logisof their expeditions, havchanged some ecologition that the French lainto two basic types, thof the north and the bsouth and west, inspiredto undertake his classic stval agricultural methods.tentionally, changes inoften affect nonhuman r

been noted, for exami

advent of the automobihuge flocks of sparrows

on the horse manure 1street.The history of ecolo;

still so rudimentary that Xabout what really happethe results were. The ext:European aurochs as I

would seem to have beenof overenthusiastic huntiintricate matters it oftento find solid informationsand years or more theHollanders have been pusNorth Sea, and the pro

SCIE:NCE:

nating in our own time in the reclama-tion of the Zuider Zee. What, if any,species of animals, birds, fish, shorelife, or plants have died out in theprocess? In their epic combat with Nep-

f tune have the Netherlanders overlookedecological values in such a way that

S the quality of human life in the Neth-erlands has suffered? I cannot discoverth;at the questions have ever been

r. asked, much less answered.People, then, have often been a dy-

namic element in their own environment,but in the present state of historicalscholarship we usually do not know

the monster exactly when, where, or with what ef-tocene from fects man-induced changes came. As,usible, if not we enter the last third of the 20th cen-at least, the tury, however, concern for the prob-!

e have been lem of ecologic backlash is mountinger than the feverishly. Natural science, conceivedwhich nature, as the effort to understand the naturehave made of things, had flourished in several eras

looding 5000 and among several peoples. Similarly, latest stage there had been an age-old accumula-many regions tion of technological skills, sometimesergrazing, the growing rapidly, sometimes slowly. Butnans to build it was not until about four genera-ns or by Cru- tions ago that Western Europe and,tics problems North America arranged a marriagere profoundly between science and technology, aes. Observa- union of the theoretical and the empiri-ndscape falls cal approaches to our natural environ-e open fields ment. The emergence in widespreadbocage of the practice of the Baconian creed thatMarc Bloch scientific knowledge means technologi-

udy of medie- cal power over nature can scarcely beQuite unin- dated before about 1850, save in thehuman ways chemical industries, where it is antici-iature. It has pated in the 18th century. Its accept-)le, that the ance gas a normal pattern of action mayile eliminated mark the greatest event in human his-that once fed tory since the invention of agriculture,ittering every and perhaps in nonhuman terrestrial

history as well.gic change is Almost at once the new situationwe know little forced the crystallization of the novelned, or what concept of ecology; indeed, the -word:inction of the ecology first appeared in the Englishlate as 1627 language in 1873. Today, less than aa simple case century later, the impact of our race

ing. On more upon the environment has so increased.is impossible in force that it has changed in es-.. For a thou- sence. When the first cannons wereFrisians and fired, in the early 14th century, they

shing back the affected ecology by sending workerscess is culmi- scrambling to the forests and moun-

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tains for more potash, sulfur, iron ore,and charcoal, with some resulting ero-sion and deforestation. Hydrogenbombs are of a different order: a warfought with them might alter the gene-tics of all life on this planet. By 1285London had a smog problem arisingfrom the burning of soft coal, but ourpresent combustion of fossil fuelsthreatens to change the chemistry ofthe globe's atmosphere as a whole,with consequences which we are onlybeginning to guess. With the popula-tion explosion, the carcinoma of plan-less urbanism, the now geologicaldeposits of sewage and garbage, surelyno creature other than man has evermanaged to foul its nest in such shortorder.

There are many calls to action, butspecific proposals, however worthy asindividual items, seem too partial, pal-liative, negative: ban the bomb, teardown the billboards, give the Hinduscontraceptives and tell them to eat theirsacred cows. The simplest solution toany suspect change is, of course, tostop it, or, better yet, to revert to aromanticized past: make those uglygasoline stations look like Anne Hatha-way's cottage or (in the Far West) likeghost-town saloons. The "wildernessarea"9 mentality invariably advocatesdeep-freezing an ecology, whether SanGimignano or the High Sierra, as itwas before the first Kleenex was drop-ped. But neither atavism nor prettifica-tion will cope with the ecologic crisisof our time.What shall we do? No one yet

knows. Unless we think about funda-mentals, our specific measures mayproduce new backlashes more seriousthan those they are designed to remedy.As a beginning we should try to

clarify our thinking by looking, insome historical depth, at the presup-positions that underlie modern tech-nology and science. Science was tradi-tionally aristocratic, speculative, intel-lectual in intent; technology was lower-class, empirical, action-oriented. Thequite sudden fusion of these two,towards the middle of the 19th cen-'iury, is surely related to the slightly?ior and contemporary democratic'evolutions which, by reducing socialarriers, tended to assert a functional

unity of brain and hand. Our ecologiccrisis is the product of an emerging,entirely novel, democratic culture. Theissue is whether a democratized worldcan survive its own implications. Pre-sumably we cannot unless we rethinkour axioms.

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The Western Traditions of

Technology and Science

One thing is so certain that it seemsstupid to verbalize it: both moderntechnology and modern science are dis-tinctively Occidental. Our technologyhas absorbed elements from all overthe world, notably from China; yeteverywhere today, whether in Japanor in Nigeria, successful technologyis Western. Our science is the heirto all the sciences of the past,especially perhaps to the work of the'great Islamic scientists of the Middle.'Ages, who so often outdid the ancient'sGreeks in skill and perspicacity: al-Razi in medicine, for example; or ibn-al-Haytham in optics; or Omar Khay-yam in mathematics. Indeed, not a few'works of such geniuses seem to havevanished in the original Arabic and tosurvive only in medieval Latin transla-tions that helped to lay the founda-tions for later Western developments.Today, around the globe, all-significantscience is Western in style and method,whatever the pigmentation or languageof the scientists.A second pair of facts is less well

recognized because they result fromquite recent historical scholarship. Theleadership of the West, both in tech-nology and in science, is far olderthan the so-called Scientific Revolutionof the 17th century or the so-calledIndustrial Revolution of the 18th cen-tury. These terms are in fact out-moded and obscure the true nature ofwhat they try to describe-significantstages in two long and separate devel-opments. By A.D. 1000 at the latest-and perhaps, feebly, as much as 200years earlier-the West began to applywater power to industrial processesother than milling grain. This was fol-lowed in the late 12th century by theharnessing of wind power. From simplebeginnings, but with remarkable con-sistency of style, the West rapidly ex-panded its skills in the developmentof power machinery, labor-savingdevices, and automation. Those whodoubt should contemplate that mostmonumental achievement in the historyof automation: the weight-driven me-chanical clock, which appeared in twoforms in the early 14th century. Notin craftsmanship but in basic techno-logical capacity, the Latin West of thelater Middle Ages far outstripped itselaborate, sophisticated, and estheti-cally magnificent sister cultures, By-zantium and Islam. In 1444 a greatGreek ecclesiastic, Bessarion, who had

gone to Italy, wrote a letter to aprince in Greece. He is amazed bythe superiority of Western ships, arms,textiles, glass. But above all he isastonished by the spectacle of water-wheels sawing timbers and pumping thebellows of blast furnaces. Clearly, hehad seen nothing of the sort in theNear East.By the end of the 15th century the

technological superiority of Europe wassuch that its small, mutually hostilenations could spill out over all the restof the world, conquering, looting, andcolonizing. The symbol of this techno-logical superiority is the fact thatPortugal, one of the weakest states ofthe Occident, was able to become, andto remain for a century, mistress ofthe East Indies. And we must remem-ber that the technology of Vasco daGama and Albuquerque was built by 4pure empiricism, drawing remarkablyf|little support or inspiration from science.1

In the present-day vernacular under-standing, modern science is supposedto have begun in 1543, when bothCopernicus and Vesalius publishedtheir great 'works. It is no derogationof their accomplishments, however, topoint out that such structures as theFabrica and the De revolutionibus donot appear overnight. The distinctiveWestern tradition of science, in fact,began in the late 11th century with amassive movement of translation ofArabic and Greek scientific works intoLatin. A *few notable books-Theo-phrastus, for example-escaped theWest's avid new appetite for 'science,but within less than 200 years effec-tively the entire corpus of Greek andMuslim science was available in Latin,and was being eagerly read and criti-cized in the new European universi-ties. Out of criticism arose new ob-servation, speculation, and increasingdistrust of ancient authorities. By thelate 13th century Europe had seizedglobal scientific leadership from the fal-tering hands of Islam. It would be asabsurd to deny the profound originalityof Newton, Galileo, or Copernicus asto deny that of the 14th century scho-lastic scientists like Buridan or Oresmeon whose work they built. Before the11th century, science scarcely existedin the Latin West, even in Romantimes. From the 11th century onward,the scientific sector of Occidental cul-ture has increased in a steady crescen-do.

Since both our technological and ourscientific movements got their start,acquired their character, and achieved

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world dominance in the Middle Ages, itwould seem that we cannot understandtheir nature or their present impactupon ecology without examining funda-mental medieval assumptions anddevelopments.

Medieval View of Man and Nature

Until recently, agriculture has beenthe chief occupation even in "ad-vanced" societies; hence, any changein methods of tillage has much im-portance. Early plows, drawn by twooxen, did not normally turn the sodbut merely scratched it. Thus, cross-

plowing was needed and fields tendedto be squarish. In the fairly light soilsand semiarid climates of the Near Eastand Mediterranean, this worked well.But such a plow was inappropriate tothe wet climate and often sticky soilsof northern Europe. By the latter partof the 7th century after Christ, how-ever, following obscure beginnings, cer-

tain northern peasants were using an

entirely new kind of plow, equippedwith a vertical knife to cut the lineof the furrow, a horizontal share toslice under the sod, and a moldboard toturn it over. The friction of this plowwith the soil was so great that itnormally required not two but eightoxen. It attacked the land with suchviolence that cross-plowing was notneeded, and fields tended to be shapedin long strips.

In the days of the scratch-plow,fields were distributed generally in unitscapable of supporting a single family.Subsistence farming was the presupposi-tion. But no peasant owned eight oxen:

to use the new and more efficient plow,peasants pooled their oxen to form largeplow-teams, originally receiving (itwould appear) plowed strips in pro-

portion to their contribution. Thus, dis-tribution of land was based no longeron the needs of a family but, rather,on the capacity of a power machineto till the earth. Man's relation to thesoil was profoundly changed. Former-ly man had been part of nature; now

he was the exploiter of nature.

Nowhere else in the world did farm-ers develop any analogous 'agriculturalimplement. Is it coincidence that mod-ern technology, with its ruthlessnesstoward nature, has so largely been pro-

duced by descendants of these peasantsof northern Europe?

This same exploitive attitude ap-pears slightly before A.D. 830 in West-ern illustrated calendars. In older calen-

10 MARCH. 1967

dars the months were shown as pas-sive personifications. The new Frankishcalendars, which set the style for theMiddle Ages, are very different: theyshow men coercing the world aroundthem-plowing, harvesting, choppingtrees, butchering pigs. Man and natureare two things, and man is master.

These novelties seem to be in har-mony with larger intellectual patterns.What people do about their ecologydepends on what they think aboutthemselves in relation to things aroundthem. Human ecology is deeply condi-tioned by beliefs about our nature anddestiny-that is, by religion. To Westerneyes this is very evident in, say, Indiaor Ceylon. It is equally true of our-selves and of our medieval ancestors.The victory of Christianity over

paganism was the greatest psychicrevolution in the history of our cul-ture. It has become fashionable todayto say that, for better or worse, welive in "the post-Christian age." Cer-tainly the forms of our thinking andlanguage have largely ceased to beChristian, but to my eye the substanceoften remains amazingly akin to thatof the past. Our daily habits of action,for example, are dominated by animplicit faith in perpetual progresswhich was unknown either to Greco-Roman antiquity or to the Orient. Itis rooted in, and is indefensible apartfrom, Judeo-Christian teleology. Thefact that Communists share it merelyhelps to show what can be demon-strated on many other grounds: thatMarxism, like Islam, is a Judeo-Chris-tian heresy. We continue today to live,as we have lived for about 1700 years,very largely in a context of Christianaxioms.What did Christianity tell people

about their relations with the environ-ment?

While many of the world's mytholo-gies provide stories of creation, Greco-Roman mythology was singularly in-coherent in this respect. Like Aristotle,the intellectuals of the ancient Westdenied that the visible world had had abeginning. Indeed, the idea of a be-ginning was impossible in the frame-work of their cyclical notion of time.In sharp contrast, Christianity inheritedfrom Judaism- not only a concept oftime as nonrepetitive and linear butalso a striking story of creation. Bygradual stages a loving and all-power-ful God had created light and dark-ness, the heavenly bodies, the earthand all its plants, animals, birds, andfishes. Finally, God had created Adam

and, as an afterthought, Eve to keepman from being lonely. Man named allthe animals, thus establishing his domi-nance over them. God planned all ofthis explicitly for man's benefit andrule: no item in the physical creationhad any purpose save to serve man'spurposes. And, although man's bodyis made of clay, he is not simply partof nature: he is made in God's image.

Especially in its Western form,Christianity is the most anthropocen-tric religion the world has seen. Asearly as the 2nd century both Tertul-lian and Saint Irenaeus of Lyons wereinsisting that when God shaped Adamhe was foreshadowing the image of theincarnate Christ, the Second Adam.Man shares, in great measure, God'stranscendence of nature. Christianity,in absolute contrast to ancient pagan-ism and Asia's religions (except,perhaps, Zoroastrianism), not only es-tablished a dualism of man and na-ture but also insisted that it is God'swill that man exploit nature for hisproper ends.At the level of the common people

this worked out in an interesting way.In Antiquity every tree, every spring,every stream, every hill had its owngenius loci, its guardian spirit. Thesespirits were accessible to men, but werevery unlike men; centaurs, fauns, andmermaids show their ambivalence. Be-fore one cut a tree, mined a mountain,or dammed a brook, it was importantto placate the spirit in charge of thatparticular situation, and to keep itplacated. By destroying pagan animism,Christianity made it possible to exploitnature in a mood of indifference to thefeelings of natural objects.

It is often said that for animism theChurch substituted the cult of saints.True; but the cult of saints is func-tionally -quite different from animism.The saint is not in natural objects; hemay have special shrines, but his citi-zenship is in heaven. Moreover, a saintis entirely a man; he can be approachedin human terms. In addition to saints,Christianity of course also had angelsand demons inherited from Judaismand perhaps, at one remove, fromZoroastrianism. But these were all asmobile as the saints themselves. Thespirits in natural objects, which for-merly had protected nature from man,evaporated. Man's effective monopolyon spirit in this world was confirmed,and the old inhibitions to the exploita-tion of nature crumbled.When one speaks in such sweeping

terms, a note of caution is in order.1205

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Christianity is a complex faith, and itsconsequences differ in differing con-texts. What I have said may well applyto the medieval West, where in facttechnology made spectacular advances.But the Greek East, a highly civilizedrealm of equal Christian devotion,seems to have produced no markedtechnological innovation after the late7th century, when Greek fire was in-vented. The key to the contrast mayperhaps be found in a difference in thetonality of piety and thought whichstudents of comparative theology findbetween the Greek and the LatinChurches. The Greeks believed that sinwas intellectual blindness, and thatsalvation was found in illumination,orthodoxy-that is, clear thinking. TheLatins, on the other hand, felt that sinwas moral evil, and that salvation wasto be found in right conduct. Easterntheology has been intellectualist. West-ern theology has been voluntarist. TheGreek saint contemplates; the Westernsaint acts. The implications of Chris-tianity for the conquest of nature wouldemerge more easily in the Westernatmosphere.The Christian dogma of creation,

which is found in the first clause ofall the Creeds, has another meaningfor our comprehension of today'secologic crisis. By revelation, God hadgiven man the Bible, the Book of Scrip-ture. But since God had made na-ture, nature also must reveal the divinementality. The religious study of na-ture for the better understanding ofGod was known as natural theology.In the early Church, and always in theGreek East, nature-was conceived pri-marily as a symbolic system throughwhich God speaks to men: the antis a sermon to sluggards; rising flamesare the symbol of the soul's aspiration.This view of nature was essentiallyartistic rather than scientific. WhileByzantium preserved and copied greatnumbers of ancient Greek scientifictexts, science as we conceive it couldscarcely flourish in such an ambience.

However, in the Latin West by theearly 13th century natural theology wasfollowing a very different bent. It wasceasing to be the decoding of thephysical symbols of God's communica-tion with man and was becoming theeffort to understand God's mind bydiscovering how his creation operates.The rainbow was no longer simply asymbol of hope first sent to Noah afterthe Deluge: Robert Grosseteste, FriarRoger Bacon, and Theodoric of Frei-

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berg produced startlingly sophisticatedwork on the optics of the rainbow, butthey did it as a venture in religiousunderstanding. From the 13th centuryonward, up to and including Leibnitzand Newton, every major scientist, ineffect, explained his motivations in reli-gious terms. Indeed, if Galileo had notbeen so expert an amateur theologianhe would have got into far less trouble:the professionals resented his intrusion.And Newton seems to have regardedhimself more as a theologian than asa scientist. It was not until the late18th century that the hypothesis of Godbecame unnecessary to many scientists.

It is often hard for the historian tojudge, when men explain why they aredoing what they want to do, whetherthey are offering real reasons or merelyculturally acceptable reasons. The con-sistency with which scientists during thelong formative centuries of Westernscience said that the task and thereward of the scientist was "to thinkGod's thoughts after him" leads oneto believe that this was their real moti-vation. If so, then modern Westernscience was cast in a matrix of Chris-tian theology. The dynamism of reli-gious devotion, shaped by the Judeo-Christian dogma of creation, gave itimpetus.

An Alternative Christian View

We would seem to be headed towardconclusions unpalatable to many Chris-tians. Since both science and technol-ogy are blessed words in our contem-porary vocabulary, some may behappy at the notions, first, that, viewedhistorically, modern science is an ex-trapolation of natural theology and,second, that modern technology is atleast partly to be explained as an Occi-dental, voluntarist realization of theChristian dogma of man's transcend-ence of, and rightful mastery over,nature. But, as we now recognize,somewhat over a century ago scienceand technology-hitherto quite separateactivities-joined to give mankind pow-ers which, to judge by many of theecologic effects, are out of control.If so, Christianity bears a huge bur-den of guilt.

I personally doubt that disastrousecologic backlash can be avoidedsimply by applying to our problemsmore science and more technology.Our science and technology have grownout of Christian attitudes toward man's

relation to nature which are almostuniversally held not only by Christiansand neo-Christians but also by thosewho fondly regard themselves as post-Christians. Despite Copernicus, all thetcosmos rotates around our little globe.Despite Darwin, we are not, in ourhearts, part of the natural process. Weare superior to nature, contemptuousof it, willing to use it for our slightestwhim. The newly elected Governor ofCalifornia, like myself a churchmanbut less troubled than I, spoke for theChristian tradition when he said (asis alleged), "when you've seen one red-wood tree, you've seen them all." To aChristian a tree can be no more than aphysical fact. The whole concept of thesacred grove is alien to Christianity andto the ethos of the West. For nearly 2millennia Christian missionaries havebeen chopping down sacred groves,which are idolatrous because they as-sume spirit in nature.What we do about ecology depends

on our ideas of the man-nature rela-tionship. More science and more tech-nology are not going to get us out ofthe present ecologic crisis until we finda new religion, or rethink our oldone. The beatniks, who are the basicrevolutionaries of our time, show asound instinct in their affinity for ZenBuddhism, which conceives of the man-nature relationship as very nearly themirror image of the Christian view.Zen, however, is as deeply conditionedby Asian history as Christianity is bythe experience of the West, and I amdubious of its viability among us.

Possibly we should ponder the great-est radical in Christian history sinceChrist: Saint Francis of Assisi. Theprime miracle of Saint Francis is thefact that he did not end at the stake,as many of his left-wing followers did.He was so clearly heretical that a Gen-eral of the Franciscan Order, SaintBonaventura, a great and perceptiveChristian, tried to suppress the earlyaccounts of Franciscanism. The key toan understanding of Francis is his be-lief in the virtue of humility notmerely for the individual but for manas a species. Francis tried to deposeman from his monarchy over creationand set up a democracy of all God'screatures. With him the ant is no long-er simply a homily for the lazy, flamesa sign of the thrust of the soul towardunion with God; now they are Broth-er Ant and Sister Fire, praising theCreator in their own ways as BrotherMan does in his.

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Later commentators have said thatFrancis preached to the birds as a re-buke to men who would not listen. Therecords do not read so: he urged thelittle birds to praise God, and in spirit-ual ecstasy they flapped their wingsand chirped rejoicing. Legends ofsaints, especially the Irish saints, hadlong told of their dealings with animalsbut always, I believe, to show theirhuman dominance over creatures. WithFrancis it is different. The land aroundGubbio in the Apennines was beingravaged by a fierce wolf. SaintFrancis, says the legend, talked to thewolf and persuaded him of the error

of his ways. The wolf repented, diedin the odor of sanctity, and was buriedin consecrated ground.What Sir Steven Ruciman calls "the

Franciscan doctrine of the animalsoul" was quickly stamped out. Quitepossibly it was in part inspired, oon-sciously or unconsciously, by the beliefin reincarnation held by the Catharheretics who at that time teemed in

Italy and southern France, and whopresumably had got it originally fromIndia. It is significant that at just thesame moment, about 1200, traces of

metempsychosis are found also inwestern Judaism, in the ProvencalCabbala. But Francis held neither totransmigration of souls nor to pan-theism. His view of nature and of manrested on a unique sort of pan-psychismof all things animate and inanimate,designed for the glorification of theirtranscendent Creator, who, in the ulti-mate gesture of cosmic humility, as-

sumed flesh, lay helpless in a manger,and hung dying on a scaffold.

I am not suggesting that many con-

temporary Americans who are con-

cerned about our ecologic crisis willbe either able or willing to counselwith wolves or exhort birds. However,the present increasing disruption of theglobal environment is the product ofa dynamic technology and science whichwere originating in the Western medi-eval world against which Saint Fran-cis was rebelling in so original a

way. Their growth cannot be under-stood historically apart from distinc-tive attitudes toward nature which are

deeply grounded in Christian dogma.The fact that most people do not thinkof these attitudes as Christian is ir-relevant. No new set of basic values

has been accepted in our society to dis-place those of Christianity. Hence we

shall continue to have a worseningecologic crisis until we reject the Chris-tian axiom that nature has no reason

for existence save to serve man.

The greatest spiritual revolutionaryin Western history, Saint Francis, pro-

posed what he thought was an alterna-tive Christian view of nature and man'srelation to it: he tried to substitute theidea of the equality of all creatures, in-cluding man, for the idea of man'slimitless rule of creation. He failed.Both our present science and our

present technology are so tincturedwith orthodox Christian arrogance

toward nature that no solution for our

ecologic crisis can be expected fromthem alone. Since the roots of our

trouble are so largely religious, theremedy must also be essentially reli-gious, whether we call it that or not.We must rethink and refeel our na-

ture and destiny. The profoundly reli-gious, but heretical, sense of the primi-tive Franciscans for the spiritual auton-omy of all parts of nature may pointa direction. I propose Francis as a

patron saint for ecologists.

One Hundred Periodic Comets

Modem techniques of observation and computation are

enabling us to clarify our ideas about these bodies.

Brian G. Marsden

Although Seneca remarked almost2000 years ago that comets were

celestial bodies that might reappear

periodically, ideas on the subject were

dominated until the 16th century by thepronouncements of Aristotle and Ptol-emy that comets were meteorologicalphenomena to be regarded as the fore-runners of disaster.The turning point came when Tycho

Brahe showed the comet of 1577 to bemore distant than Moon. Tycho sup-

posed it to travel about Sun in a circularorbit somewhat larger than that ofVenus. Curiously enough, Kepler never

10 MARCH 1967

applied his laws of planetary motion tocomets and believed them to move

through the solar system in straightlines. Some of Kepler's contemporaries,however, such as Horatio Grassi andWilliam Lower, held that cometaryorbits were indeed ellipses.

It was of course Newton who settledthe question by demonstrating that thecomet of 1680 moved, in accordancewith the law of gravitation, in an orbitthat was an ellipse of such great eccen-

tricity that it could be approximated bya parabola. Shortly afterwards, in thecourse of his celebrated calculations on

a number of comets, Halley noticed aresemblance among the orbits of thecomets of 1531, 1607, and 1682; hededuced these to be one and the samebody and predicted that it would returnabout the year 1758.

Other predictions, based on thesimilarity of various pairs of cometaryorbits, were made from time to time byseveral astronomers during the 18th and19th centuries. The futility of this prac-tice was finally pointed out in the 1860'sby Hoek (1). He suggested that therewere many instances in which cometstraveled essentially in the same orbit;presumably they were fragments ofsome comet that had disintegrated. Theexistence of these "comet groups" ren-ders it impossible to decide whether twocomets with similar orbits are identicalor not, unless the revolution period ofone of them can be derived unequiv-ocally from the observations.The first comet for which a meaning-

ful elliptical orbit was obtained directlyfrom observations was one discoveredby Messier in 1770. Considerable diffi-

The author is an astronomer at the Smith-sonian Astrophysical Observatory, Cambridge,Massachusetts, and lecturer on astronomy atHarvard University.

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