After ten years of comparing his own records with those of several other astronomers, Bessel was able to prove that there existed systematic and consistent differences between the speed with which each of them reacted to observed events; and he also succeeded in establishing the characteristic reaction-time -- called 'the personal equation' -- of several of his colleagues.
These studies were continued by other astronomers over the next thirty years, in the course of which the development of more precise, automatic recording instruments made it possible to arrive at 'absolute personal equations'. Finally, fifty years after Bessel's discovery, von Helmholtz published a paper showing that the rate of conduction of impulses in nerves was of a definite, measurable order -- and not, as had previously been assumed, practically instantaneous. Helmholtz was well acquainted with the work that astronomers had done on personal equations, and his experiments on the propagation of impulses in motor and sensory nerves followed their procedure and techniques. Helmholtz's discovery inaugurated the era of 'mental chronometry', and was a decisive step in the progress of neurophysiology and experimental psychology.
In a similar manner the basic advances in our knowledge of infectious diseases were mostly due to the importation of experimental techniques which had been developed for quite different purposes -- such as the use of filtering procedures, microscopic techniques, tissue-cultures and the statistical methods employed in genetics.
Bartlett, in Thinking -- An Experimental and Social Study (1958), gave a series of similar illustrations. The conclusions at which he arrived seem to paraphrase the thesis of the present theory that bisociation is the essence of creative activity:
As experimental science has gained wider and wider fields, and won increasing recognition, it has often happened that critical stages for advance are reached when what has been called one body of knowledge can be brought into close and effective relationship with what has been treated as a different, and a largely or wholly independent, scientific discipline. . . . The alert experimenter is always on the lookout for points and areas of overlap, between things and processes which natural and unaided observations has tended to treat merely, or chiefly, as different. . . . One of the most important features of these turning points in experimental development is that they very often introduce methods and instrumentation new to the field of research involved, but already developed in some other region of investigation. . . . The winding progress of any branch of experimental science is made up essentially by a relatively small number of original inquiries, which may be widely separated, followed, as a rule, by a very large number of routine inquiries. The most important feature of original experimental thinking is the discovery of overlap and agreement where formerly only isolation and difference were recognized. This usually means that when any experimental science is ripe for marked advance, a mass of routine thinking belonging to an immediately preceding phase has come near to wearing itself out by exploiting a limited range of techniques to establish more and more minute and specialized detail. A stage has been reached in which finding out further details adds little or nothing to what is known already. . . . However, at the same time, perhaps in some other branch of science, and perhaps in some hitherto disconnected part of what is treated as the same branch, there are other techniques generating their own problems, opening up their own gaps. An original mind, never wholly contained in any one conventionally enclosed field of interest, now seizes upon the possibility that there may be some unsuspected overlap, takes the risk whether there is or not, and gives the old subject-matter a new look. Routine starts again. . . . The conditions for original thinking are when two or more streams of research begin to offer evidence that they may converge and so in some manner be combined. It is the combination which can generate new directions of research, and through these it may be found that basic units and activities may have properties not before suspected which open up a lot of new questions for experimental study. [6]
But I must add to this a word of warning. Except when it is merely a matter of borrowing, so to speak, an existing technique or laboratory equipment from a neighbouring science (as in most of Bartlett's examples), the integration of matrices is not a simple operation of adding together. It is a process of mutual interference and cross-fertilization, in the course of which both matrices are transformed in various ways and degrees. Hidden axioms, implied in the old codes, suddenly stand revealed and are subsequently dropped; the rules of the game are revised before they enter as sub-rules into the composite game. When Einstein bisociated energy and matter, both acquired a new look in the process.
The Thinking Cap
I have repeatedly mentioned 'shifts of attention' to previously neglected aspects of experience which make familiar phenomena appear in a new, revealing light, seen through spectacles of a different colour. At the decisive turning points in the history of science, all the data in the field, unchanged in themselves, may fall into a new pattern, and be given a new interpretation, a new theoretical frame.
By stressing the importance of the interpretation (or reinterpretation) of facts, I may have given the impression of underestimating the importance of collecting facts, of having emphasized the value of theory-making at the expense of the empirical aspect of science -- an unforgivable heresy in the eyes of Positivists, Behaviourists, and other theorists of the anti-theory school. Needless to say, only a fool could belittle the importance of observation and experiment -- or wish to revert to Aristotelian physics which was all speculation and no experiment. But the collecting of data is a discriminating activity, like the picking of flowers, and unlike the action of a lawn-mower; and the selection of flowers considered worth picking, as well as their arrangement into a bouquet, are ultimately matters of personal taste. As T. H. Huxley has said in an oft-quoted passage:
Those who refuse to go beyond fact rarely get as far as fact; and anyone who has studied the history of science knows that almost every step therein has been made by . . . the invention of a hypothesis which, though verifiable, often had little foundation to start with. . . .
Sir Lawrence Bragg is the only physicist who shared a Nobel Prize with his own father -- for their joint work on analysing crystal structures by means of X-rays, doubtless an eminently factual preoccupation, which took two lifetimes. Yet in his book on The History of Science he too concluded that the essence of science 'lies not in discovering facts, but in discovering new ways of thinking about them'. [7]
New facts do emerge constantly; but they are found as the result of a search in a definite direction, based on theoretical considerations -- as Galle discovered the planet Neptune, which nobody had seen before, by directing his telescope at the celestial region which Leverrier's calculations had indicated.* This is admittedly an extreme case of observation guided by theory; but it remains nevertheless true that it is not enough for the scientist to keep his eyes open unless he has an idea of what he is looking for.
The telescope is, of course, the supreme eye-opener and fact-finder in astronomy; but it is rarely appreciated that the Copernican revolution came before the invention of the telescope -- and so did Kepler's New Astronomy. The instruments which Copernicus used for observing the stars were less precise than those of the Alexadrian astronomers Hypparchus and Ptolemy, on whose data Copernicus built his theory; and he knew no more about the actual motions of stars and planets than they had known:
Insofar as actual knowledge is concerned, Copernicus was no better off, and in some respects worse off, than the Greek astronomers of Alexandria who lived in the time of Jesns Christ. They had the same data, the same instruments, the same know-how in geometry, as he did. They were giants of 'exact science'; yet they failed to see what Copernicus saw after, and Aristarchus had seen before them: that the planets' motions were obviously governed by the sun. [8]
Similarly, Harvey's revolutionary discoveries were made before the microscope was developed into a serviceable tool; and Einstein formulated his 'Special Theory of Relativity' in 1905 ba
sed on data which, as I have already said, were by no means new. Poincaré, for instance, Einstein's senior by twenty-five years, had held all the loose threads in his hands, and the reasons for his failure to tie them together are still a matter of speculation among scientists. To quote Taton:
Poincaré, who had so much wider a mathematical background than Einstein, then a young assistant in the Federal Patents Office of Berne, knew all the elements required for such a synthesis, of which he had felt the urgent need and for which he had laid the first foundations. Nevertheless, he did not dare to explain his thoughts, and to derive all the consequences, thus missing the decisive step separating him from the real discovery of the principle of relativity. [9]
Without the hard little bits of marble which are called 'facts' or 'data' one cannot compose a mosaic; what matters, however, are not so much the individual bits, but the successive patterns into which you arrange them, then break them up and rearrange them. 'We shall find', wrote Butterfield on the opening page of his history of the Scientific Revolution, 'that in both celestial and terrestrial physics -- which hold the strategic place in the whole movement -- change is brought about, not by new observations or additional evidence in the first instance, but by transpositions that were taking place inside the minds of the scientists themselves. . . . Of all forms of mental activity, the most difficult to induce even in the minds of the young, who may be presumed not to have lost their flexibility, is the art of handling the same bundle of data as before, but placing them in a new system of relations with one another by giving them a different framework, all of which virtually means putting on a different kind of thinking-cap for the moment. It is easy to teach anybody a new fact about Richelieu, but it needs light from heaven to enable a teacher to break the old framework in which the student has been accustomed to seeing his Richelieu.' [10]
Once more we are facing the stubborn powers of habit, and the antithesis of habit and originality. New facts alone do not make a new theory; and new facts alone do not destroy an outlived theory. In both cases it requires creative originality to achieve the task. The facts which proved that the planetary motions depended on the sun have been staring into the face of astronomers throughout the ages -- but they preferred to look away.
The Pathology of Thought
I have discussed 'snowblindness' and faulty integrations on the individual level. In the evolution of the collective matrices of science, similar aberrations occur on an historic scale, and are transmitted from one generation to the next -- sometimes over a number of centuries. Indeed, some of the most important discoveries consisted in the elimination of psychological road-blocks -- in uncovering what had always been there.
The classic example of a mental road-block, extending over two millennia, is one to which I have repeatedly alluded before. If one had to sum up the history of scientific ideas about the universe in a single sentence, one could only say that up to the seventeenth century our vision was Aristotelian, after that Newtonian. It would, of course, be naïve to blame the giant figure of the Stagyrite for crystallizing trends in Greek thought which were originated by others, and reflected the intellectual mood of Greece at the disastrous period before and immediately after the Macedonian conquest. The reasons why his absurd theory of physics acquired such a firm hold over medieval Europe I have discussed elsewhere; [10a] they do not enter into our present context.
The central postulate of the theory was that a moving body will immediately revert to immobility when it ceases to be pushed or pulled along by a second body, its 'mover'. Now an ox-cart on a muddy road will indeed come to a halt when its movers, the oxen, are unyoked. But an arrow will fly through the air once the initial impulse has been imparted to it -- whereas, according to Aristotelian physics, it should have dropped to earth the very instant it parted from the bow, its mover. The answer to this objection was that the initial motion of the arrow, while still on the bow, created a disturbance in the air, a kind of vortex, which now became the arrow's 'mover', and pulled it along its course. Not before the fourteenth century was the further objection raised that if the arrow (or spear, or catapulted stone) was pulled by an air-current, it could never fly against the wind.
This inability to perceive that a moving body tends to persist in its course was the psychological road-block which prevented the emergence of a true science of physics from the fourth century B.C. to the seventeenth century A.D. Yet every soldier who threw a spear felt that the thing had a momentum of its own -- and so, of course, did the victim whom it hit; and every traveller in a post-coach which came to an abrupt halt, had experienced to his sorrow that his motion continued after the mover's had stopped. The experience, the bodily 'feel' of inertial momentum is as old as mankind -- but it was prevented from becoming conscious and explicit knowledge by the mental block built into the collective matrix. Even Galileo saw only part of the truth: he thought that a moving body, left to itself in empty space, would persist not in straight, but in circular motion. Such are the difficulties of clearing away the man-made heaps of rubble under which some simple truth lies buried.
The necessity for every moving body to be constantly accompanied and pushed along by a 'mover' also applied to the stars; it created a 'universe in which unseen hands had to be in constant operation'. [11] The planets had to be rolled along their orbits, like beer-barrels, by a host of angels; even Kepler needed a heavenly broomstick, wielded by the sun, to sweep them round their path. Yet here again, the knowledge of centrifugal force has always existed, ever since children swung stones round at the end of a string; and this knowledge had even been explicitly formulated in antiquity. In his treatise On the Face in the Disc of the Moon, Plutarch, who took a great interest in science and particularly in astronomy, wrote that the moon was of solid stuff, like the earth; and that the reason why it did not fall down on the earth, in spite of its weight, was as follows:
. . . The moon has a security against falling in her very motion and the swing of her revolutions, just as objects put in slings are prevented from falling by the circular whirl; for everything is carried along by the motion natural to it if it is not deflected by anything else. Thus the moon is not carried down by her weight because her natural tendency is frustrated by her revolution. [12] (my italics)
The translation is by Heath, who remarks: 'This is practically Newton's first Law of Motion.' It is curious that this passage has aroused so little comment.
Perhaps the most disastrous feature of the Aristotelian system was its denial that the whole universe was made out of the same basic stuff (as Parmenides and the Atomists had asserted before him) and to split the world into two parts, divided by a kind of metaphysical iron curtain. The 'sublunary' region (the earth and its vicinity) was made of four unstable elements, the skies of a fifth, permanent ether; the sublunary region was infected with the vice of change -- an abominable slum where generation, corruption, and decay never stopped, whereas on the other side of the curtain, fifty-five celestial intelligences were spinning round as many pure, crystalline spheres, carrying the planets and stars in their unchanging circular orbits.
It was the most dramatic splitting operation the world had seen since Lucifer was expelled from heaven; and it was unavoidably followed by a series of divorces and remarriages between incompatible partners. Celestial mechanics became dissociated from sublunary physics and married to theology when Aristotle's 'first mover' became identified with God, and his star-spinning spirits with the hierarchy of angels. Terrestrial physics, in its turn, was divorced from mathematics, and married to animism. The most striking fact about pre-Renaissance science is indeed its complete indifference to quantitative measurements and numerical relations -- not to mention experiment and observation; and its obsession with ascribing animate powers to inanimate objects. Stones fell to earth because it was their natural home, as flames rose upward because their home was in the sky; and the stone accelerated its fall because it was hurrying home as horses hurry to their stable. All motion, all change, was
due to a purposeful striving of objects to realize what was potentially inherent in their nature, to move 'from potency to act' -- a principle derived by specious analogy from embryonic development. It took about three centuries (from Occam to Newton) to undo the tangled mess which these divorces and mésalliances had brought about.
In the healthy evolution of a science, we observe a branching out of specialized, relatively autonomous lines of research; and a parallel process of confluences and integrations mediated by the discovery of universal principles underlying variety. But we also find pathological developments of a rather drastic and persistent kind in the history of scientific thought -- collective mental blockages which keep apart what belongs together, and lead to the segregation of 'closed systems'. The healthy periods in the growth of a science remind one of the differentiation of structure and integration of function in organic development. In the unhealthy periods, on the other hand, we find dissociation instead of differentiation, and faulty integrations.
Some of the latter were the result of shotgun-marriages, as it were -- imposed from outside, by religions or political pressures. Medieval astronomy had to embrace theology, Soviet biology was wedded to a crude form of Lamarckism. The development of science cannot be isolated from its historic context, from the climate of a given age or civilization; it influences and is influenced by its philosophy, religion, art, social organization, economic needs. But scientific thinking nevertheless enjoys a considerable amount of autonomy; its tortuous progress is unpredictable, its victories and defeats are of its own making. The reason why Copernicus postponed the publication of his theory till the end of his life was not fear of the Catholic Church (which encouraged and protected him) but the fear of ridicule from his fellow astronomers. Galileo's conflict with the Church could have probably been avoided if he had been endowed with less passion and more diplomacy; but long before that conflict started, he had incurred the implacable hostility of the orthodox Aristotelians who held key positions at the Italian universities. Religious and political oppression play only an incidental part in the history of science; its erratic course and recurrent crises are caused by internal factors. [13]