268 I ATURE FEH. 18, 1939, \ 'oL. 143

Natural Philosophy and Human Cultures*

By Prof. Niels Bohr, For. Mem. R.S.

J T is only wiLh great ho.~ itai i on that I haYe for our general outlook i" common!.\' realized. it accepted a. kind invitaLion to address t his is scarcely yet so as rogardH tho unsuspectt'd assembly of distinguished reprcsenlati,·cs of tho epistemological lesson which tho opening of quite anthropological and ethnographical sciences of now realm s of phyHical ro::;oarch has given us in which I , as a physicist,. have of course no first-hand tho most recent years. Our penetration into the knowledge. Still, on this specia,l occasion. when world of atoms. hitherto closed to t.he oyo of man cYon tho historical smroundings speak to everyone is indeed an adventure wh ich may bo compared of us about aspoct.s of lifo other than those discussed with the great journoyil of discovery of the aL tho regular congress proceedings, it might. circumnavigators and t h(' bolnatural philosophy and tho art of physical experimentation has not only it s bearing on general human problems. Notwith­ romO\'Od t ho last traces of tho old holiof that the "tanding t ho great separation between ou r different coarse n r~s of our ~o;cnsrs would for over prcren hm nchcs of knowledge, the new lesson which has us from obtaining direct. information nbou hcon impressed upon phy,;icists regarding t.hc i.ndi,idual atoms, hut has o,·cn shown us that the raution wit h which all usual com·entions must be atoms themsel>cs consiHt of still smaller corpu>clel appli ed as soon as we aro not concerned with which can be isolated and tho properties of whiti o,·eryday oxpericnco, may, indeed, bo suited to can be innstigated separately. At the same time remind us in a noYel way of tho dangers, well wo hphysics, aro only valid wbell Of course it is impossible to distinguish sharply dealing with bodies consisting of practically • between natural philosophy and human culture. infinite numbers of atoms. The new knowledgt Tho physical sciences are, in fact, an integral part concerning the bcha,·iour of single atoms and of our oivilizat.ion, not only beca.uso om· over atomic corpuscles has, in fact., revealed an UJI. incrca. ing mastery of the forces of Xa Luro has so expected limit for t ho suhdi,~i s ion of all physilll C'O mplet r l.'· changed the material conditions of act.ions extending far beyond t.ho old doctrine of l·•• lifo, but a lso because the study of t hose sciences t ho limited di,·isibility of m.altor, and ghing err11 I,. has contributed so much to clarify t ho background atomic process a peculiar individual chnracl« IJ .• of our own existence. \Vh at has it. not meant in This discovery bas, in fa,ct, yielded a quite new ,..•• '.. this respect., that we no more consider oursoh-es basis for the u ndorstanding of tho intrinsic stability a;; pri\Tilcgcd in linng altho cent ro of the uni,·er ~e. of atomic structures, which, in t.ho last ralOrl, surrounded by less fortunate societies inha.biting condit.ions the rcgularit.ies of a ll ordinary experiellf8. the edges of t.he abyss, but t hat t hrough the How radical a change in our aLt itude towards 1M deYclopmonl of astronomy and geography wo have description of Nat uro this dovolopmont of at011110 realized that wo aro all sharing a smreasons to renounce tho idea.! of causality every physical phenomenon on tho point of view but in tho study of atomic phenomena. we of tho observer, has contributed so largely lo the repeatedly been taught that questions which unity and beauty of our whole world-picture. believed to have received long ago their \ Vh ilo the importance of t hese great achiovomonts answers had most unexpected surpri ·, • \duress giwn at Kronborg Castl<· during tlw cxcuf'oi on to EJ,ino r<' ;;tore for us. You will smely all have of t he int.cmntional Congress of An thropological and Ethnoiu~ical ~cirncr•, ! ·oJ)('nhngen, .\ ugumatter which have puzzled interacting wit h t he objects also enter essentially. physicists so much in recent years. Tho apparent This last fact gives tho straightforward explanation contradictions which we have met in this respect of the apparent contradictions which appear when are, in fact, as acute as those -whi ch gave rise to results about atomic objects obtained by different the developm ent of tho theory of relativity in t he experimental arrangements are tentatively com­ beginning of this century, and have, just as the bined into a self-contained picture of the object. latter, only fo und their explanation by a closer Information regobservation. analogies by which one has tried to visualize the We are here faced with an epistemological individual radiative effects which has, in fact, led JIOblem quite now in natural philosophy, where to an entirely satisfactory solution of the riddles •description of experiences has so far boon based of the properties of light alluded to above. In the 1p011 the assumption, already inherent in ordinary same way, it is only by taking into considera­ lllventions of language, that it is possible to tion tho complementary relationship between the sharply between the behaviour of different experiences concerning the behan our of and tho moans of observation. This atomic corpuscles, that it has been possible to •mpt1on is not only fully justified by all eYcry­ obtain a clue to tho understanding of the striking experience, but oven constitutes tho whole contrast botweon the properties of ordinary of classical physics, which, just through t he mechanical models and the peculiar laws of of relativity, has recoi,'ed such a wonderful stability governing atomic structures which form • J)letiion. As soon as we begin to deal, however, tho basis for every closer explanation of t ho phenomena like individual atomic processes specific physical and chemical properties of matter. duo to their very nature, are essentially Of course I have no intention, on this occasion, •muled by the interaction between t ho objects of entering more closely into such details, but I question and the measuring instruments hope that I have boon able to give a sufficiently for tho definition of tho oxporimontal clear impression of tho fact that wo aro horo in wo aro forced to examine more no way concerned with an arbit rary renunciation tho question of what kind of knowledge as regards t ho dotttiled analysis of tho almost obtained concerning t hese objects. In this overwhelming richness of our rapidly increasing we must, on one hand, realize that tho oxperionco in tho realm of atoms. On the contrary, of overy physical experiment-to gain know­ we havo to do with a rational development of under reproducible and communicable con­ our means of classifying and comprehending new •&-teaoves us no choice but to uso everyday experience which, due to its very character, finds eventually refined by t ho terminology of no place within the frame of causal description physics, not only in all accounts of t he suit.ed only to accow1t for the behaviour of objects llll'llction and manipulation of tho measuring so long as this behaviour is independent of tho but also in tho description of the means of obscn'ation. F ar from containing any experimental results. On t he other hand, mysticism contrary to the spirit of science, tho il equally important to understand that just viewpoint of 'complementarity' forms indeed a circumstance implies t hat no result of an consistent generalization of the ideal of causality. concerning a phenomenon which, in However unexpected this development may lies outside the range of classical physics, appear in the domain of physics, I am sure that as giving information about many of you will have recognized the close analogy properties of the object; but is between the situation as regards t he analysis of connected with a definite situation in atomic phenomena, which I have described, and lldei!Cri]~tio>n of which the measuring instruments characteristic features of t ho pwblem of observation 270 NATURE FEB. 18, 1939, \"oL. 143 in human psychology. Indeed, we may say that the to draw a sharp separation between animals &M trend of modern psychology can be characterized man; but of course our power of speech plaal as a reaction against the attempt at analysing us in this respect in an essentially differtlli psychical experience into elements which can be situation, not only as regards the exchange associated in the same way as are the results of practical experience, but also and above all • measurements in classical physics. In introspection, regards the possibility of transmitting throui it is clearly impossible to distinguish sharply education to children the traditions conce~ between t he phenomena themselves and their behaviour and reasoning which form the blil conscious perception, and although we may of any human culture. often speak of lending our attention to some As regards reason compared with instinct, particular aspect of a psychical experience, it is, above all, essential to realize that no pro,. will appear on closer examination that we really human thinking is imaginable without the use have to do, in such cases, with mutually exclusive concepts framed in some language which eVfiiJ situations. We all know the old saying that, if generation has to learn anew. This use of conceJ* we try to analyse our own emotions, we scarcely is, in fact, not only to a large extent suppretlliJI possess them any longer , and in that sense we instinctive life, but stands even largely in an recognize between psychical experiences, for elusive relationship of complementarity to the description of which words such as 'thoughts' display of inherited instincts. The and 'feelings' are adequately used, a complementary superiority of lower animals compared with maD relationship similar to that between the experiences utilizing the possibilities of Nature for the maintel­ regarding the behaviour of atoms obtained under ance and propagation of life has certainly different experimental arrangements and described true explanation in the fact that, for such by means of different analogies taken from our we ca1mot speak of any conscious thinking in usual ideas. By such a comparison it is, of course, sense of the word. At the same time, the in no way intended to suggest any closer relation capacity of so-called primitive people to between atomic physics and psychology, but themselves in forests or deserts, which, merely to stress an epistemological argument apparently lost in more civilized societies, common to both fields, and thus to encourage us on occasion be revived in any of us, might to sec how far the solution of t he relatively eimple the conclusion that such feats are only physical problems may be helpful in clarifying the when no recourse is taken to conceptual t more intricate psychological questions with which which on its side is adapted to far more ' human life confronts us, and which anthropologists purposes of primary importance for the ! and ethnologists so often meet in their investiga­ ment of civilization. Just because it is n~ I tions . awake to the use of concepts, a new-born Coming now closer to our subject of the bearing can scarcely be reckoned as a human being; • of such viewpoints on the comparison of different belonging to the species of man, it has, of • human cultures, we shall first stress the typical though more helpless a creature than most complementary relationship between the modes animals, the organic possibilities of := II of behaviour of living beings characterized by the through education a culture which enables n II words 'instinct' and 'reason'. It is true that these take its place in somo human society. words are used in very different senses ; thus Such considerations confront us at once with instinct may mean motive power or inherited question whether the widespread belief that behaviour, and reason may denote deeper sense child is born with a predisposition for the as well as conscious argumentation. What we are of a specific human culture is really wta•·•v•..... concerned with is, however, only the practical or whether one has not rather to assume that way in which these words are used to discriminate culture can be implanted and thrive on between the different situations in which animals different physical backgrounds. Here we are and men find themselves. Of course, nobody will course touching a subject of still unsettled deny our belonging to the animal world, and it troversies between geneticists, who pursue would even be very difficult to find an exhaustive interesting studies on the inheritance of definition characterizing man among the other characters. In connexion with such discUSidlj animals. Indeed, the latent possibilities in any however, we must above all bear in mind thal living organism are not easily estimated, and I distinction between t he concepts genotype think that t here is none of us who has not some­ phenotype, so fruitful for the clari.ficatioo times been deeply impressed by the extent to heredity in plants and animals, essentially which circus animals can be drilled. Not even supposes the subordinate influence of the with respect to the conveyance of information conditions of life on the characteristic from one individual to another would it be possible of the species. In tho case of the specific Xo. 3616, FEB. 18, 1939 )JATURE 271 ebaracters of human societies the problem is, inseparability of objective content and observing lmever, reversed in the sense t.hat the basis for subject, prevents an immediate application of lbe classification is here the traditional habits the conventions suited to accounting for experiences lhaped by the histories of the societies and their of daily life. Especially in the study of cultures of Datura! environments. These habits, as well as primitive peoples, ethnologists aro, indeed, not lbeir inherent presuppositions, must therefore be only aware of the risk of corrupting such cultures analyfed in detail before any possible influence of by the necessary contact, but are even confronted ilherited biological differences on the development with the problem of the reaction of such studies and maintenance of the cultures concerned can on their own human attitude. What I here allude Mestimated. Indeed, in characterizing different to is the experience, well known to explorers, of lations and even different families within a nation, the shaking of their hitherto unrealized prejudices Ill may to a large extent consider anthropological through t he experience of the unsuspected inner hits and spiritual traditions as independent of harmony human life can present even under other, and it would even be tempting to conventions and traditions most radically different by definition the adjective 'human' for from their own. As a specially drastic example those characters which are not directly bound I may perhaps here recall the extent to which in bodily inheritance. certain societies the roles of men and women are At first sight, it might perhaps appear that such reversed, not only regarding domestic and social attitude would mean unduly stressing merely duties but also regarding behaviour and mentality. points. But tho lesson which we have Even if many of us, in such a situation, might from the whole growth of t he physical perhaps at first shrink from admitting the possi­ is that the germ of fruitful development bility that it is entirely a caprice of fate that the lies just in the proper choice of definitions. people concerned have their specific culture and we think, for example, of tho clarification not ours, and we not theirs instead of our own, it about in various branches of science by is clear that even the slightest suspicion in this of relativity theory, we see respect implies a betrayal of the national com­ what advance may lie in such formal placency inherent in any human cult ure resting As I have already hinted earlier in in itself. address, relativistic viewpoints are certainly Using the word much as it is used, in atomic helpful in promoting a more objective attitude physics, to characterize the relationship between w relationships between human cultures, the experiences obtained by different experimental differences of which in many ways arrangements and capable of visualization only the different equivalent modes in which by mutually exclusive ideas, we may truly say experience can be described. Still, this that different human cultures are complementary between physical and humanistic problems to each other. Indeed, each such culture represents limited scope and its exaggeration has even a harmonious balance of traditional conventions to misunderstandings of t he essence of the by means of which latent potentialities of human of relativity itself. The unity of the life can unfold themselves in a way which reveals I world picture, in fact, implies the to us now aspects of its unlimited richness and II for any one observer to predict within variety. Of course, there cannot, in this domain, own conceptual frame how any other observer be any question of such ·absolutely exclusive co-ordinate experience within the frame relationships as those between complementary to him. The main obstacle to an unpreju­ experiences about the behaviour of well-defined attitude towards the relation between various atomic objects, since scarcely any culture exists cultures is, however, the deep-rooted which could be said to be fully self-contained. of the traditional backgrounds on On the contrary, it is well known from numerous the cultural harmony in different human examples how a more or less intimate contact is based and which exclude any simple between different human societies can lead to a between such cultures. gradual fusion of traditions, giving birth to a above all in this connexion that the quite new culture. The importance in this respect of complementarity offers itself as a of the mixing of populations through emigration of coping with the situation. In fact, or conquest for the advancement of human studying human cultures different from our civilization need scarcely be recalled. It is, indeed, we have to deal with a particular problem perhaps the greatest prospect of humanistic observation which on closer consideration studies, to contribute through an increasing many features in common with atomic or knowledge of the history of cultural development problems, where the interaction to that gradual removal of prejudices which is objects and measuring tools, or the t he common aim of all science. 272 FEB. 18, 1939, \'oL. 143

As I stressed in tho beginning of this address, ceptual frame, I referred jokingly to the traditional it is, of course, far beyond my capacities to con­ prejudices which the Danes cherish with regard tribute in any direct way to tho solution of tho to their Swedish brothers on the other side of the problems discussed among the experts at this beautiful Sound outside these windows, wi.. congress. My only purpose has been to give an whom we have fought through centuries eren impression of a general epistemological attitude within the walls of t his castle, and from contael which we have been forced to adopt in a field as with whom we have, through the ages, recei-red far from human passions as the analysis of simple so much fruitful inspiration. Now you will realize physical experiments. I do not know, however, what a shock I got when, after my address, a whether I have found the right words to convey member of the audience came up to me and sail this impression, and before I conclude, I may that he could not understand why I hated the perhaps be allowed to relate an experience which Swedes. Obviously I must have expressed m~ once most vividly reminded me of my deficiencies most confusingly on that occasion, and I am afraid in this respect. In order to explain to an audience that also to-day I have talked in a very obsctm that I did not use the word 'prej udice' to imply way. Still, I hope that I have not spoken liD any condemnation of other cultures, but merely obscurely as to give rise to any such misunder­ to characterize our necessarily prejudiced con- standings of the trend of my argument.

Modern Trends m Air Transport* •• I ' MOST modern air transport is by means of the the cube of these. This relationship, known as llle I' aeroplane, a body heavier than air, de­ squarejcube law, implies that with weight increu­ I pending upon forward movement for sustentation. ing at a greater rate than lift, t he carrying capacny For purposes of this examination it can be con­ of any wing system will ultimately be reduced •• sidered to consist of four fundamentally different zero. The functioning of this law is being systems : (I) the lifting system, that is, the wings; by designers by the more efficient distribution (2) the non-lifting system, principally t he body, a the materials in the structure, the use of ~ structure with space for the load, a girder carrying fically stronger (strengthjweight) materials, ... the tail control units, and often the power plant ; improved aerodynamic design allowing increaa (3) the propulsive system comprising the engines speed for the same power, and consequently em and airscrews; (4) the control system, including lift from tho same wing area. This is further helped all devices by which the pilot governs t he move­ by the fact that the power required is a factor rl ments of his aircraft. The trend in development the wing area, and its weight is only increasing • of each of these is examined from t he point of the square of t he linear dimensions of the machiDL view of its approach towards air transport ideals Increase in angle of attack, as a m e:-hod of obtaia­ of carrying capacity, speed, range, economy, ing additional lift, results in an increase in comfort and safety. of the wing at such a rate that the weight of The lift of a wing increases with its area, the extra power plant necessary to overcome it square of the speed, and, in general, its angle of cancels out its extra lift. As an example, attack. Increase of lift therefore demands some post-War commercial aeroplanes weighed combination of larger values of these. It must be three to five thousand pounds with a wing remembered that carrying capacity is not gross of eight to twelve pounds per square foot, lift ; but rather the surplus of the total lift over there was evidence that the optimum size that necessary to sustain the weight of the struc­ the squarejcube law was already approaching. ture, engines, etc. Assuming wing structures new Boeing flying boat, now building, will wet' carrying the same load per unit area, with the 82,000 lb. with a carrying capacity of 10,000 same geometry of structure and materials of while some projected designs for construction, while the lift will increase as the services are of 200,000 lb. total weight and square of the dimensions, the volume, and con­ to carry a pay load of 25,000 lb., with wing sequently the weight, of the wing will increase as of 30-40 lb. per square foot. The question of speeds is one of con1menill • l'ased on a lecture by Prof. W. F. Durand, emeritus professor of mechanical engineering in Stanford University, given at the recent requirements. They have risen from 50-80 meeting of the American Association for the Advancement of Science, llichmond, Virginia. per hour to 150-200 miles per hour normal