History of Civilization in England, Vol. 3 of 3

by Henry Thomas Buckle

Thus, again, inasmuch as heat becomes latent, and flies from the senses, not only when ice is passing into water, but also when water is passing into steam, we find in this latter circumstance, one of the reasons why man and other animals can live in the tropics, which, but for this, would be deserted. They are constantly suffering from the heat which is collected in their bodies, and which, considered by itself, is enough to destroy them. But this heat causes thirst, and they consequently swallow great quantities of fluid, much of which exudes through the pores of the skin in the form of vapour. And as, according to the theory of latent heat, vapour cannot be produced without a vast amount of heat being buried within it, such vapour absorbs and carries off from the body, that which, if left in the system, would prove fatal. To this we must add, that, in the tropics, the evaporation of water is necessarily rapid, and the vapour which is thus produced, becomes another storehouse of heat, and a vehicle by which it is removed from the earth, and prevented from unduly interfering with the economy of life.[765]

From these and many other arguments, all of which were so essentially speculative, and dealt with such hidden processes of nature, that even now we are not justified either in confidently admitting them or in positively denying them, Black was led to that great doctrine of the indestructibility of heat,[766] which, as I have pointed out, has, in its connexion with the indestructibility of force, a moral and social importance even superior to its scientific value. Though the evidence of which he was possessed was far more scanty than what we now have, he, by the reach of his commanding intellect, rather than by the number and accuracy of his facts, became so penetrated with a conviction of the stability of physical affairs, that he not only applied that idea to the subtle phenomena of heat, but, what was much harder to do, he applied it to cases in which heat so entirely escapes the senses, that man has no cognizance of it, except through the medium of the imagination. According to his view, heat passes through an immense variety of changes, during which it appears to be lost; changes which no eye can ever see, which no touch can ever experience, and which no instrument can ever measure. Still, and in the midst of all these changes, it remains intact. From it nothing can be taken, and to it nothing can be added. In one of those fine passages of his Lectures, which, badly reported as they are,[767] bear the impress of his elevated genius, Black, after stating what would probably happen, if the total amount of heat existing in the world were to be diminished, proceeds to speculate on the consequences of its being increased. Were it possible for any power to add to it ever so little, it would at once overstep its bounds; the equilibrium would be disturbed; the framework of affairs would be disjointed. The evil rapidly increasing, and acting with accumulated force, nothing would be able to stop its ravages. It must continue to gain ground, till all other principles are absorbed and conquered. Sweeping on, unhindered, and irresistible, before it, every animal must perish, the whole vegetable world must disappear, the waters must pass into vapour, and the solid parts of the globe be merged and melted, until, at length, the glorious fabric, loosened and dissolved, would fall away, and return to that original chaos out of which it had been evolved.[768]

These, like many other of the speculations of this great thinker, will find small favour with those purely inductive philosophers, who not only suppose, perhaps rightly, that all our knowledge is in its beginning built upon facts, but who countenance, what seems to me, the very dangerous opinion, that every increase of knowledge must be preceded by an increase of facts. To such men it will appear, that Black had far better have occupied himself in making new observations, or devising new experiments, than in thus indulging his imagination in wild and unprofitable dreams. They will think, that these flights of fancy are suitable, indeed, to the poet, but unworthy of that severe accuracy, and of that close attention to facts, which ought to characterize a philosopher. In England, especially, there is, among physical inquirers, an avowed determination to separate philosophy from poetry, and to look upon them, not only as different, but as hostile. Among that class of thinkers, whose zeal and ability are beyond all praise, and to whom we owe almost unbounded obligations, there does undoubtedly exist a very strong opinion, that, in their own pursuit, the imagination is extremely dangerous, as leading to speculations, of which the basis is not yet assured, and generating a desire to catch too eagerly at distant glimpses before the intermediate ground has been traversed. That the imagination has this tendency is undeniable. But they who object to it on this account, and who would, therefore, divorce poetry from philosophy, have, I apprehend, taken a too limited view of the functions of the human mind, and of the manner in which truth is obtained. There is, in poetry, a divine and prophetic power, and an insight into the turn and aspect of things, which, if properly used, would make it the ally of science instead of the enemy. By the poet, nature is contemplated on the side of the emotions; by the man of science, on the side of the understanding. But the emotions are as much a part of us as the understanding: they are as truthful; they are as likely to be right. Though their view is different, it is not capricious. They obey fixed laws; they follow an orderly and uniform course; they run in sequences; they have their logic and method of inference. Poetry, therefore, is a part of philosophy, simply because the emotions are a part of the mind. If the man of science despises their teaching, so much the worse for him. He has only half his weapons; his arsenal is unfilled. Conquests, indeed, he may make, because his native strength may compensate the defects of his equipment. But his success would be more complete and more rapid, if he were properly furnished and made ready for the battle. And I cannot but regard as the worst intellectual symptom of this great country, what I must venture to call the imperfect education of physical philosophers, as exhibited both in their writings and in their trains of thought. This is the more serious, because they, as a body, form the most important class in England, whether we look at their ability, or at the benefits we have received from them, or at the influence they are exercising, and are likely to exercise, over the progress of society. It cannot, however, be concealed, that they display an inordinate respect for experiments, an undue love of minute detail, and a disposition to overrate the inventors of new instruments, and the discoverers of new, but often insignificant, facts. Their predecessors of the seventeenth century, by using hypotheses more boldly, and by indulging their imagination more frequently, did certainly effect greater things, in comparison with the then state of knowledge, than our contemporaries, with much superior resources, have been able to achieve. The magnificent generalizations of Newton and Harvey could never have been completed in an age absorbed in one unvarying round of experiments and observations. We are in that predicament, that our facts have outstripped our knowledge, and are now encumbering its march. The publications of our scientific institutions, and of our scientific authors, overflow with minute and countless details, which perplex the judgment, and which no memory can retain. In vain do we demand that they should be generalized, and reduced into order. Instead of that, the heap continues to swell. We want ideas, and we get more facts. We hear constantly of what nature is doing, but we rarely hear of what man is thinking. Owing to the indefatigable industry of this and the preceding century, we are in possession of a huge and incoherent mass of observations, which have been stored up with great care, but which, until they are connected by some presiding idea, will be utterly useless. The most effective way of turning them to account, would be to give more scope to the imagination, and incorporate the spirit of poetry with the spirit of science. By this means, our philosophers would double their resources, instead of working, as now, maimed, and with only half their nature. They fear the imagination, on account of its tendency to form hasty theories. But, surely, all our faculties are needed in the pursuit of truth, and we cannot be justified in discrediting any part of the human mind. And I can hardly doubt, that one of the reasons why we, in England, made such wonderful discoveries during the seventeenth century, was because that century was also the great age of English poetry. The two mightiest intellects our country has produced are Shakspeare and Newton; and that Shakspeare should have preceded Newton, was, I believe, no casual or unmeaning event. Shakspeare and the poets sowed the seed, which Newton and the philosophers reaped. Discarding the old scholastic and theological pursuits, they drew attention to nature, and thus became the real founders of all natural science. They did even more than this. They first impregnated the mind of England with bold and lofty conceptions. They taught the men of their generation to crave after the unseen. They taught them to pine for the ideal, and to rise above the visible world of sense. In this way, by cultivating the emotions, they opened one of the paths which lead to truth. The impetus which they communicated, survived their own day, and, like all great movements, was felt in every department of thought. But now it is gone; and, unless I am greatly mistaken, physical science is at present suffering from its absence. Since the seventeenth century, we have had no poet of the highest order, though Shelley, had he lived, would perhaps have become one. He had something of that burning passion, that sacred fire, which kindles the soul, as though it came fresh from the altar of the gods. But he was cut off in his early prime, when his splendid genius was still in its dawn. If we except his immature, though marvellous, efforts, we may assuredly say, that, for nearly two hundred years, England has produced no poetry which bears those unmistakable marks of inspiration which we find in Spenser, in Shakspeare, and in Milton. The result is, that we, separated by so long an interval from those great feeders of the imagination, who nurtured our ancestors, and being unable to enter fully into the feelings of poets, who wrote when nearly all opinions, and, therefore, nearly all forms of emotion, were very different to what they now are, cannot possibly sympathize with those immortal productions so closely as their contemporaries did. The noble English poetry of the sixteenth and seventeenth centuries is read more than ever, but it does not colour our thoughts; it does not shape our understandings, as it shaped the understandings of our forefathers. Between us and them is a chasm, which we cannot entirely bridge. We are so far removed from the associations amid which those poems were composed, that they do not flash upon us with that reality and distinctness of aim, which they would have done, had we lived when they were written. Their garb is strange, and belongs to another time. Not merely their dialect and their dress, but their very complexion and their inmost sentiments, tell of bygone days, of which we have no firm hold. There is, no doubt, a certain ornamental culture, which the most highly educated persons receive from the literature of the past, and by which they sometimes refine their taste, and sometimes enlarge their ideas. But the real culture of a great people, that which supplies each generation with its principal strength, consists of what is learnt from the generation immediately preceding. Though we are often unconscious of the process, we build nearly all our conceptions on the basis recognized by those who went just before us. Our closest contact is, not with our forefathers, but with our fathers. To them we are linked by a genuine affinity, which, being spontaneous, costs us no effort, and from which, indeed, we cannot escape. We inherit their notions, and modify them, just as they modified the notions of their predecessors. At each successive modification, something is lost and something is gained, until, at length, the original type almost disappears. Therefore it is, that ideas entertained several generations ago, bear about the same relation to us, as ideas preserved in a foreign literature. In both cases, the ideas may adorn our knowledge, but they are never so thoroughly incorporated with our minds, as to be the knowledge itself. The assimilation is incomplete, because the sympathy is incomplete. We have now no great poets; and our poverty in this respect is not compensated by the fact, that we once had them, and that we may, and do, read their works. The movement has gone by; the charm is broken; the bond of union, though not cancelled, is seriously weakened. Hence, our age, great as it is, and, in nearly all respects, greater than any the world has yet seen, has, notwithstanding its large and generous sentiments, its unexampled toleration, its love of liberty, and its profuse, and almost reckless, charity, a certain material, unimaginative, and unheroic character, which has made several observers tremble for the future. So far as I can understand our present condition, I do not participate in these fears, because I believe that the good we have already gained, is beyond all comparison greater than what we have lost. But that something has been lost, is unquestionable. We have lost much of that imagination, which, though, in practical life, it often misleads, is, in speculative life, one of the highest of all qualities, being suggestive as well as creative. Even practically, we should cherish it, because the commerce of the affections mainly depends on it. It is, however, declining; while, at the same time, the increasing refinement of society accustoms us more and more to suppress our emotions, lest they should be disagreeable to others. And as the play of the emotions is the chief study of the poet, we see, in this circumstance, another reason which makes it difficult to rival that great body of poetry which our ancestors possessed. Therefore, it is doubly incumbent on physical philosophers to cultivate the imagination. It is a duty they owe to their own pursuits, which would be enriched and invigorated by such an enlargement of their resources. It is also a duty which they owe to society in general; since they, whose intellectual influence is already greater than that of any other class, and whose authority is perceptibly on the increase, might have power enough to correct the most serious deficiency of the present age, and to make us some amends for our inability to produce such a splendid imaginative literature as that which our forefathers created, and in which the choicest spirits of the seventeenth century did, if I may so say, dwell and have their being.

If, therefore, Black had done nothing more than set the example of a great physical philosopher giving free scope to the imagination, he would have conferred upon us a boon, the magnitude of which it is not easy to overrate. And it is very remarkable, that, before he died, that department of inorganic physics, which he cultivated with such success, was taken up by another eminent Scotchman, who pursued exactly the same plan, though with somewhat inferior genius. I allude, of course, to Leslie, whose researches on heat are well known to those who are occupied with this subject; while, for our present purpose, they are chiefly interesting as illustrating that peculiar method which, in the eighteenth century, seemed essential to the Scotch mind.

About thirty years after Black propounded his famous theory of heat, Leslie began to investigate the same topic, and, in 1804, published a special dissertation upon it.[769] In that work, and in some papers in his Treatises on Philosophy, are contained his views, several of which are now known to be inaccurate,[770] though some are of sufficient value to mark an epoch in the history of science. Such was his generalization respecting the connexion between the radiation of heat, and its reflection; bodies which reflect it most, radiating it least, and those which radiate it most, reflecting it least. Such, too, was another wide conclusion, which the best inquirers have since confirmed, namely, that, while heat is radiating from a body, the intensity of each ray is as the sine of the angle which it makes with the surface of that body.

These were important steps, and they were the result of experiments, preceded by large and judicious hypotheses. In relation, however, to the economy of nature, considered as a whole, they are of small account in comparison with what Leslie effected towards consolidating the great idea of light and heat being identical, and thus preparing his contemporaries for that theory of the interchange of forces, which is the capital intellectual achievement of the nineteenth century. But it is interesting to observe, that, with all his ardour, he could not go beyond a certain length. He was so hampered by the material tendencies of his time, that he could not bring himself to conceive heat as a purely supersensual force, of which temperature was the external manifestation.[771] For this, the age was barely ripe. We accordingly find him asserting, that heat is an elastic fluid, extremely subtle, but still a fluid.[772] His real merit was, that, notwithstanding the difficulties which beset his path, he firmly seized the great truth, that there is no fundamental difference between light and heat. As he puts it, each is merely a metamorphosis of the other. Heat is light in complete repose. Light is heat in rapid motion. Directly light is combined with a body, it becomes heat; but when it is thrown off from that body, it again becomes light.[773]

Whether this is true or false, we cannot tell; and many years, perhaps many generations, will have to elapse before we shall be able to tell. But the service rendered by Leslie is quite independent of the accuracy of his opinion, as to the manner in which light and heat are interchanged. That they are interchanged, is the essential and paramount idea. And we must remember, that he made this idea the basis of his researches, at a period when some very important facts, or, I should rather say, some very conspicuous facts, were opposed to it; while the main facts which favoured it were still unknown. When he composed his work, the analogies between light and heat, with which we are now acquainted, had not been discovered; no one being aware, that double refraction, polarization, and other curious properties, are common to both. To grasp so wide a truth in the face of such obstacles, was a rare stroke of sagacity. But, on account of the obstacles, the inductive mind of England refused to receive the truth, as it was not generalized from a survey of all the facts. And Leslie, unfortunately for himself, died too soon to enjoy the exquisite pleasure of witnessing the empirical corroboration of his doctrine by direct experiment, although he clearly perceived that the march of discovery, in reference to polarization, was leading the scientific world to a point, of which his keen eye had discerned the nature, when, to others, it was an almost invisible speck, dim in the distant offing.[774]

In regard to the method adopted by Leslie, he assures us, that, in assuming the principles from which he reasoned, he derived great aid from poetry; for he knew that the poets are, after their own manner, consummate observers, and that their united observations form a treasury of truths, which are nowise inferior to the truths of science, and of which science must either avail herself, or else suffer from neglecting them.[775] To apply these truths rightly, and to fit them to the exigencies of physical inquiry, is, no doubt, a most difficult task, since it involves nothing less than holding the balance between the conflicting claims of the emotions and the understanding. Like all great enterprises, it is full of danger, and, if undertaken by an ordinary mind, would certainly fail. But there are two circumstances which make it less dangerous in our time, than in any earlier period. The first circumstance is, that the supremacy of the human understanding, and its right to judge all theories for itself, is now more generally admitted than ever; so that there can be little fear of our leaning to the opposite side, and allowing poetry to encroach on science. The other circumstance is, that our knowledge of the laws of nature is much greater than that possessed by any previous age; and there is, consequently, less risk of the imagination leading us into error, inasmuch as we have a large number of well-ascertained truths, which we can confront with every speculation, no matter how plausible or ingenious it may appear.

On both these grounds, Leslie was, I apprehend, justified in taking the course which he did. At all events, it is certain, that, by following it, he came nearer than would otherwise have been possible, to the conceptions of the most advanced scientific thinkers of our day. He distinctly recognized that, in the material world, there is neither break nor pause; so that what we call the divisions of nature have no existence, except in our minds.[776] He was even almost prepared to do away with that imaginary difference between the organic and inorganic world, which still troubles many of our physicists, and prevents them from comprehending the unity and uninterrupted march of affairs. They, with their old notions of inanimate matter, are unable to see that all matter is living, and that what we term death is a mere expression by which we signify a fresh form of life. Towards this conclusion, all our knowledge is now converging; and it is certainly no small merit in Leslie, that he, sixty years ago, when really comprehensive views, embracing the whole creation, were scarcely known among scientific men, should have strongly insisted that all forces are of the same kind, and that we have no right to distinguish between them, as if some were living, and others were dead.[777]

We owe much to him, by whom such views were advocated. But they were then, and in a certain, though far smaller degree, they are now, so out of the domain of physical experience, that Leslie never could have obtained them by generalizing in the way which the inductive philosophy enjoins. His great work on heat was executed, as well as conceived, on the opposite plan;[778] and his prejudices on this point were so strong, that we are assured by his biographer, that he would allow no merit to Bacon, who organized the inductive method into a system, and to whose authority we in England pay a willing, and I had almost said a servile, homage.[779]