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History of Civilization in England, Vol. 3 of 3

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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

Another curious illustration of the skill with which the Scotch mind, when once possessed of a principle, worked from it deductively, appears in the geological speculations of Hutton, late in the eighteenth century. It is well known, that the two great powers which have altered the condition of our planet, and made it what it is, are fire and water. Each has played so considerable a part, that we can hardly measure their relative importance. Judging, however, from the present appearance of the crust of the earth, there is reason to believe, that the older rocks are chiefly the result of fusion, and that the younger are aqueous deposits. It is, therefore, not unlikely, that, in the order in which the energies of nature have unfolded themselves, fire preceded water, and was its necessary precursor.780 But, all that we are as yet justified in asserting is, that these two causes, the igneous and the aqueous, were in full operation long before man existed, and are still busily working. Perhaps they are preparing another change in our habitation, suitable to new forms of life, as superior to man, as man is superior to the beings who occupied the earth before his time. Be this as it may, fire and water are the two most important and most general principles with which geologists are concerned; and though, on a superficial view, each is extremely destructive, it is certain that they can really destroy nothing, but can only decompose and recompose; shifting the arrangements of nature, but leaving nature herself intact. Whether one of these elements will ever again get the upper hand of its opponent, is a speculation of extreme interest. For, there is reason to suspect, that, at one period, fire was more active than water, and that, at another period, water was more active than fire. That they are engaged in incessant warfare, is a fact with which geologists are perfectly familiar, though, in this, as in many other cases, the poets were the first to discern the truth. To the eye of the geologist, water is constantly labouring to reduce all the inequalities of the earth to a single level; while fire, with its volcanic action, is equally busy in restoring those inequalities, by throwing up matter to the surface, and in various ways disturbing the crust of the globe.781 And as the beauty of the material world mainly depends on that irregularity of aspect, without which scenery would have presented no variety of form, and but little variety of colour, we shall, I think, not be guilty of too refined a subtlety, if we say that fire, by saving us from the monotony to which water would have condemned us, has been the remote cause of that development of the imagination which has given us our poetry, our painting, and our sculpture, and has thereby not only wonderfully increased the pleasures of life, but has imparted to the human mind a completeness of function, to which, in the absence of such a stimulus, it could not have attained.

When geologists began to study the laws according to which fire and water had altered the structure of the earth, two different courses were open to them, namely, the inductive and the deductive. The deductive plan was to compute the probable consequences of fire and water, by reasoning from the sciences of thermotics and hydrodynamics; tracking each element by an independent line of argument, and afterwards coördinating into a single scheme the results which had been separately obtained. It would then only remain to inquire, how far this imaginary scheme harmonized with the actual state of things; and if the discrepancy between the ideal and the actual were not greater than might fairly be expected from the perturbations produced by other causes, the ratiocination would be complete, and geology would, in its inorganic department, become a deductive science. That our knowledge is ripe for such a process, I am far, indeed, from supposing; but this is the path which a deductive mind would take, so far as it was able. On the other hand, an inductive mind, instead of beginning with fire and water, would begin with the effects which fire and water had produced, and would first study these two agents, not in their own separate sciences, but in their united action as exhibited on the crust of the earth. An inquirer of this sort would assume, that the best way of arriving at truth would be to proceed from effects to causes, observing what had actually happened, and rising from the complex results up to a knowledge of the simple agents, by whose power the results have been brought about.

 

If the reader has followed the train of thought which I have endeavoured to establish in this chapter, and in the first volume, he will be prepared to expect that when, in the latter half of the eighteenth century, geology was first seriously studied, the inductive plan of proceeding from effects to causes became the favourite one in England; while the deductive plan of proceeding from causes to effects, was adopted in Scotland and in Germany. And such was really the case. It is generally admitted, that, in England, scientific geology owes its origin to William Smith, whose mind was singularly averse to system, and who, believing that the best way of understanding former causes was to study present effects, occupied himself, between the years 1790 and 1815, in a laborious examination of different strata.782 In 1815, he, after traversing the whole of England on foot, published the first complete geological map which ever appeared, and thus took the first great step towards accumulating the materials for an inductive generalization.783 In 1807, and, therefore, before he had brought his arduous task to an end, there was formed in London the Geological Society, the express object of which, we are assured, was, to observe the condition of the earth, but by no means to generalize the causes which had produced that condition.784 The resolution was, perhaps, a wise one. At all events, it was highly characteristic of the sober and patient spirit of the English intellect. With what energy and unsparing toil it has been executed, and how the most eminent members of the Geological Society have, in the pursuit of truth, not only explored every part of Europe, but examined the shell of the earth in America and in Northern Asia, is well known to all who are interested in these matters; nor can it be denied, that the great works of Lyell and Murchison prove that the men who are capable of such laborious enterprises, are also capable of the still more difficult achievement of generalizing their facts and refining them into ideas. They did not go as mere observers, but they went with the noble object of making their observations subservient to a discovery of the laws of nature. That was their aim; and all honour be to them for it. Still, it is evident, that their process is essentially inductive; it is a procedure from the observation of complex phenomena, up to the elements to which those phenomena are owing; it is, in other words, a study of natural effects, in order to learn the operation of natural causes.

Very different was the process in Germany and Scotland. In 1787, that is, only three years before William Smith began his labours, Werner, by his work on the classification of mountains, laid the foundation of the German school of geology.785 His influence was immense; and among his pupils we find the names of Mohs, Raumer, and Von Buch, and even that of Alexander Humboldt.786 But the geological theory which he propounded, depended entirely on a chain of argument from cause to effect. He assumed, that all the great changes through which the earth had passed, were due to the action of water. Taking this for granted, he reasoned deductively from premisses with which his knowledge of water supplied him. Without entering into details respecting his system, it is enough to say, that, according to it, there was originally one vast and primeval sea, which, in the course of time, deposited the primitive rocks. The base of all was granite; then gneiss; and others followed in their order. In the bosom of the water, which at first was tranquil, agitations gradually arose, which, destroying part of the earliest deposits, gave birth to new rocks, formed out of their ruins. The stratified thus succeeded to the unstratified, and something like variety was established. Then came another period, in which the face of the waters, instead of being merely agitated, was convulsed by tempests, and, amid their play and collision, life was generated, and plants and animals sprung into existence. The vast solitude was slowly peopled, the sea gradually retired; and a foundation was laid for that epoch, during which man entered the scene, bringing with him the rudiments of order and of social improvement.787

These were the leading views of a system which, we must remember, exercised great sway in the scientific world, and won over to its side minds of considerable power. Erroneous and far-fetched though it was, it had the merit of calling attention to one of the two chief principles which have determined the present condition of our planet. It had the further merit of provoking a controversy, which was eminently serviceable to the interests of truth. For, the great enemy of knowledge is not error, but inertness. All that we want is discussion, and then we are sure to do well, no matter what our blunders may be. One error conflicts with another; each destroys its opponent, and truth is evolved. This is the course of the human mind, and it is from this point of view that the authors of new ideas, the proposers of new contrivances, and the originators of new heresies, are benefactors of their species. Whether they are right or wrong, is the least part of the question. They tend to excite the mind; they open up the faculties; they stimulate us to fresh inquiry; they place old subjects under new aspects; they disturb the public sloth; and they interrupt, rudely, but with most salutary effect, that love of routine, which, by inducing men to go grovelling on in the ways of their ancestors, stands in the path of every improvement, as a constant, an outlying, and, too often, a fatal obstacle.

The method adopted by Werner was evidently deductive, since he argued from a supposed cause, and reasoned from it to the effects. In that cause, he found his major premiss, and thence he worked downwards to his conclusion, until he reached the world of sense and of reality. He trusted in his one great idea, and he handled that idea with consummate skill. On that very account, did he pay less attention to existing facts. Had he chosen, he, like other men, could have collected them, and subjected them to an inductive generalization. But he preferred the opposite path. To reproach him with this is irrational; for, in his journey after truth, he chose one of the only two roads which are open to the human mind. In England, indeed, we are apt to take for granted that one road is infinitely preferable to the other. It may be so; but on this, as on many other subjects, assertions are current which have never been proved. At all events, Werner was so satisfied with his method, that he would not be at the pains of examining the position of rocks and their strata, as they are variously exhibited in different countries; he did not even explore his own country, but, confining himself to a corner of Germany, he began and completed his celebrated system, without investigating the facts on which, according to the inductive method, that system should have been built.788

Exactly the same process, on the same subject, and at the same time, was going on in Scotland. Hutton, who was the founder of Scotch geology, and who, in 1788, published his Theory of the Earth, conducted the inquiry just as Werner did; though, when he began his speculations, he had no knowledge of what Werner was doing.789 The only difference between them was, that while Werner reasoned from the agency of water, Hutton reasoned from the agency of fire. The cause of this may, I think, be explained. Hutton lived in a country where some of the most important laws of heat had, for the first time, been generalized, and where consequently, that department of inorganic physics had acquired great reputation. It was natural for a Scotchman to take more than ordinary interest in a subject in which Scotland had been so successful, and had obtained so much fame. We need not, therefore, wonder that Hutton, who, like all men, felt the intellectual bent of the time in which he lived, should have yielded to an influence of which he was, perhaps, unconscious. In obedience to the general mental habits of his country he adopted the deductive method. In further obedience to the more special circumstances connected with his own immediate pursuits, he gathered the principles from which he reasoned from a study of fire, instead of gathering them, as Werner did, from a study of water.

Hence it is, that, in the history of geology, the followers of Werner are known as Neptunists, and those of Hutton as Plutonists.790 And these terms represent the only difference between the two great masters. In the most important points, namely their method, they were entirely agreed. Both were essentially one-sided; both paid a too exclusive attention to one of the two principal agents which have altered, and are still altering, the crust of the earth; both reasoned from those agents, instead of reasoning to them; and both constructed their system without sufficiently studying the actual and existing facts; committing, in this respect, an error which the English geologists were the first to rectify.

As I am writing a history, not of science, but of scientific method, I can only briefly glance at the nature of those services which Hutton rendered to geology, and which are so considerable, that his system has been called its present basis.791 This, however, is too strongly expressed; for, though Hutton was far from denying the influence of water,792 he did not concede enough to it, and there is a tendency among several geologists to admit that the system of Werner considered as an aqueous theory, contains a larger amount of truth than the advocates of the igneous theory are willing to allow. Still, what Hutton did was most remarkable, especially in reference to what are now termed metamorphic rocks, the theory of whose formation he was the first to conceive.793 Into this, and into their connexion, on the one hand, with the sedimentary rocks, and, on the other hand, with those rocks whose origin is perhaps purely igneous, I could not enter without treading on debatable ground. But, putting aside what is yet uncertain, I will mention two circumstances respecting Hutton which are undisputed, and which will give some idea of his method, and of the turn of his mind. The first circumstance is, that, although he ascribed to subterranean heat, as exhibited in volcanic action, a greater and more constant energy than any previous inquirers had ventured to do,794 he preferred speculating on the probable consequences of that action, rather than drawing inferences from the facts which the action presented; he being on this point so indifferent, that he arrived at his conclusions without inspecting even a single region of active volcanoes, where he might have watched the workings of nature, and seen what she was really about.795 The other circumstance is equally characteristic. Hutton, in his speculations concerning the geological effects of heat, naturally availed himself of the laws which Black had unfolded. One of those laws was, that certain earths owe their fusibility to the presence of fixed air in them before heat has expelled it; so that if it were possible to force them to retain their fixed air, or carbonic acid gas, as we now call it, no amount of heat could deprive them of the capability of being fused. The fertile mind of Hutton saw, in this discovery, a principle from which he could construct a geological argument. It occurred to him, that great pressure would prevent the escape of fixed air from heated rocks, and would thus enable them to be fused, notwithstanding their elevated temperature. He then supposed that, at a period anterior to the existence of man, such a process had taken place under the surface of the sea, and that the weight of so great a column of water had prevented the rocks from being decomposed while they were subjected to the action of fire. In this way, their volatile parts were held together, and they themselves might be melted, which could not have happened except for this enormous pressure. By following this line of argument, he accounted for the consolidation of strata by heat; since, according to the premisses from which he started, the oily, or bituminous parts, would remain, in spite of the efforts of heat to disperse them.796 This striking speculation led to the inference, that the volatile components of a substance, and its fixed components, may be made to cohere, in the very teeth of that apparently irresistible agent whose business it is to effect their separation. Such an inference was contrary to all experience; or, to say the least, no man had ever seen an instance of it.797 Indeed, the event was only supposed to happen in consequence of circumstances which were never met with on the surface of the globe, and which, therefore, were out of the range of all human observation.798 The utmost that could be expected was, that, by means of our instruments, we might, perhaps, on a small scale, imitate the process which Hutton had imagined. It was possible, that a direct experiment might artificially combine great pressure with great heat, and that the result might be, that the senses would realize what the intellect had conceived.799 But the experiment had never been tried, and Hutton, who delighted in reasoning from ideas rather than from facts, was not likely to undertake it.800 He cast his speculation on the world, and left it to its fate.801 Fortunately, however, for the reception of his system, a very ingenious and skilful experimenter of that day, Sir James Hall, determined to test the speculation by an appeal to facts; and as nature did not supply the facts which he wanted, he created them for himself. He applied heat to powdered chalk, while, at the same time, with great delicacy of manipulation, he subjected the chalk to a pressure about equal to the weight of a column of water half a mile high. The result was, that, under that pressure, the volatile parts of the chalk were held together; the carbonic acid gas was unable to escape; the generation of quicklime was stopped; the ordinary operations of nature were baffled, and the whole composition, being preserved in its integrity, was fused, and, on subsequently cooling, actually crystallized into solid marble.802 Never was triumph more complete. Never did a fact more fully confirm an idea.803 But, in the mind of Hutton, the idea preceded the fact by a long interval; since, before the fact was known, the theory had been raised, and the system which was built upon it had, indeed, been published several years. It, therefore, appears that one of the chief parts of the Huttonian Theory, and certainly its most successful part, was conceived in opposition to all preceding experience; that it pre-supposed a combination of events which no one had ever observed, and the mere possibility of which nothing but artificial experiment could prove; and, finally, that Hutton was so confident of the validity of his own method of inquiry, that he disdained to make the experiment himself, but left to another mind that empirical branch of the investigation which he deemed of little moment, but which we, in England, are taught to believe is the only safe foundation of physical research.804

I have now given an account of all the most important discoveries made by Scotland, in the eighteenth century, respecting the laws of the inorganic world. I have said nothing of Watt, because, although the steam-engine, which we owe to him, is of incalculable importance, it is not a discovery, but an invention. An invention it may justly be termed, rather than an improvement.805 Notwithstanding what had been effected in the seventeenth century, by De Caus, Worcester, Papin, and Savery, and notwithstanding the later additions of Newcomen and others, the real originality of Watt is unimpeachable. His engine was, essentially, a new invention; but, under its scientific aspect, it was merely a skilful adaptation of laws previously known; and one of its most important points, namely, the economy of heat, was a practical application of ideas promulgated by Black.806 The only discovery made by Watt, was that of the composition of water. Though his claims are disputed by the friends of Cavendish, it would appear that he was the first who ascertained that water, instead of being an element, is a compound of two gases.807 This discovery was a considerable step in the history of chemical analysis, but it neither involved nor suggested any new law of nature, and has, therefore, no claim to mark an epoch in the history of the human mind.808 There is, however, one circumstance connected with it which is too characteristic to be passed over in silence. The discovery was made in 1783, by Watt, the Scotchman, and by Cavendish, the Englishman, neither of whom seems to have been aware of what the other was doing.809 But between the two there was this difference. Watt, for several years previously, had been speculating on the subject of water in connexion with air, and having, by Black's law of latent heat, associated them together, he was prepared to believe that one is convertible into the other.810 The idea of an intimate analogy between the two bodies having once entered his mind, gradually ripened; and when he, at last, completed the discovery, it was merely by reasoning from data which others possessed besides himself. Instead of bringing to light new facts, he drew new conclusions from former ideas.811 Cavendish, on the other hand, obtained his result by the method natural to an Englishman. He did not venture to draw a fresh inference, until he had first ascertained some fresh facts. Indeed, his discovery was so completely an induction from his own experiments, that he omitted to take into consideration the theory of latent heat, from which Watt had reasoned, and where that eminent Scotchman had found the premisses of his argument.812 Both of these great inquirers arrived at truth, but each accomplished his journey by a different path. And this antithesis is accurately expressed by one of the most celebrated of living chemists, who, in his remarks on the composition of water, truly says, that while Cavendish established the facts, Watt established the idea.813

769. Mr. Napier, in his Memoirs of Leslie, pp. 16, 17 (prefixed to Leslie's Treatises on Philosophy, Edinb. 1838), says, that he ‘composed the bulk of his celebrated work on Heat in the years 1801 and 1802;’ but that, in 1793, he propounded ‘some of its theoretical opinions, as well as the germs of its discoveries.’ It appears, however, from his own statement, that he was making experiments on heat, at all events, as early as 1791. See Leslie's Experimental Inquiry into the Nature and Propagation of Heat, London, 1804, p. 409.
770. For specimens of some of his most indefensible speculations, see Leslie's Treatises on Philosophy, pp. 38, 43.
771. Though he clearly distinguishes between the two. ‘It is almost superfluous to remark, that the term heat is of ambiguous import, denoting either a certain sensation, or the external cause which excites it.’ Leslie on Heat, p. 137.
772. ‘Heat is an elastic fluid extremely subtle and active.’ Leslie on Heat, p. 150. At p. 31, ‘calorific and frigorific fluid.’ See also pp. 143, 144; and the attempt to measure its elasticity, in pp. 177, 178.
773. ‘Heat is only light in the state of combination.’ Leslie on Heat, p. 162. ‘Heat in the state of emission constitutes light.’ p. 174. ‘It is, therefore, the same subtle matter, that, according to its different modes of existence, constitutes either heat or light. Projected with rapid celerity, it forms light; in the state of combination with bodies it acts as heat.’ p. 188. See also p. 403, ‘different states of the same identical substance.’
774. In 1814, that is ten years after his great work was published, and about twenty years after it was begun, he writes from Paris: ‘My book on heat is better known’ here ‘than in England. I was even reminded of some passages in it which in England were considered as fanciful, but which the recent discoveries on the polarity of light have confirmed.’ Napier's Memoirs of Leslie, p. 28, prefixed to Leslie's Philosophical Treatises, edit. Edinb. 1838. Leslie died in 1832 (p. 40); and the decisive experiments of Forbes and Melloni were made between 1834 and 1836.
775. ‘The easiest mode of conceiving the subject, is to consider the heat that permeates all bodies, and unites with them in various proportions, as merely the subtle fluid of light in a state of combination. When forcibly discharged, or suddenly elicited from any substance, it again resumes its radiant splendour.’ … ‘The same notion was embraced by the poets, and gives sublimity to their finest odes.’ … ‘Those poetical images which have descended to our own times, were hence founded on a close observation of nature. Modern philosophy need not disdain to adopt them, and has only to expand and reduce to precision the original conceptions.’ Leslie's Treatises on Philosophy, pp. 308, 309. Again, at p. 416: ‘This is not the first occasion in which we have to admire, through the veil of poetical imagery, the sagacity and penetration of those early sages. It would be weakness to expect nice conclusions in the infancy of science; but it is arrogant presumption to regard all the efforts of unaided genius with disdain.’
776. ‘We should recollect that, in all her productions, Nature exhibits a chain of perpetual gradation, and that the systematic divisions and limitations are entirely artificial, and designed merely to assist the memory and facilitate our conceptions.’ Leslie on Heat, p. 506.
777. ‘All forces are radically of the same kind, and the distinction of them into living and dead is not grounded on just principles.’ Leslie on Heat, p. 133. Compare p. 299: ‘We shall perhaps find, that this prejudice, like many others, has some semblance of truth; and that even dead or inorganic substances must, in their recondite arrangements, exert such varying energies, and so like sensation itself, as if fully unveiled to our eyes, could not fail to strike us with wonder and surprise.’
778. Mr. Napier, in his Life of Leslie, p. 17, says of it, very gravely, ‘Its hypotheses are not warranted by the sober maxims of inductive logic.’
779. ‘Notwithstanding the contrary testimony, explicitly recorded by the founders of the English experimental school, he denied all merit and influence to the immortal delineator of the inductive logic.’ Napier's Life of Leslie, p. 42.
780. The supposition, that volcanic agencies were formerly more potent than they are now, is by no means inconsistent with the scientific doctrine of uniformity, though it is generally considered to be so. It is one thing to assert the uniformity of natural laws; it is quite another thing to assert the uniformity of natural causes. Heat may once have produced far greater effects than it can do at present, and yet the laws of nature be unchanged, and the order and sequence of events unbroken. What I would venture to suggest to geologists is, that they have not taken sufficiently into account the theory of the interchange of forces, which seems to offer a solution of at least part of the problem. For, by that theory, a large portion of the heat which formerly existed may have been metamorphosed into other forces, such as light, chemical affinity, and gravitation. The increase of these forces consequent on the diminution of heat, would have facilitated the consolidation of matter; and until such forces possessed a certain energy, water, which afterwards became so prominent, could not have been formed. If the power of chemical affinity, for instance, were much weaker than it is, water would assuredly resolve itself into its component gases. Without wishing to lay too much stress on this speculation, I submit it to the consideration of competent judges, because I am convinced that any hypothesis, not absolutely inconsistent with the known laws of nature, is preferable to that dogma of interference, which what may be called the miraculous school of geologists wish to foist upon us, in utter ignorance of its incompatibility with the conclusions of the most advanced minds in other departments of thought. The remarks in Sir Roderick Murchison's great work (Siluria, London, 1854, pp. 475, 476) on the ‘grander intensity of former causation,’ and on the difficulty this opposes to the ‘uniformitarians,’ apply merely to those who take for granted that each force has always been equally powerful: they do not affect those who suppose that it is only the aggregate of force which remains unimpaired. Though the distribution of forces may be altered, their gross amount is not susceptible of change, so far as the highest conceptions of our actual science extend. Consequently, there is no need for us to believe that, in different periods, the intensity of causation varies; though we may believe that some one agent, such as heat, had at one time more energy than it has ever had since.
781. ‘The great agents of change in the inorganic world may be divided into two principal classes, the aqueous and the igneous. To the aqueous belong rain, rivers, torrents, springs, currents, and tides; to the igneous, volcanos and earthquakes. Both these classes are instruments of decay as well as of reproduction; but they may also be regarded as antagonist forces. For the aqueous agents are incessantly labouring to reduce the inequalities of the earth's surface to a level; while the igneous are equally active in restoring the unevenness of the external crust, partly by heaping up new matter in certain localities, and partly by depressing one portion, and forcing out another, of the earth's envelope.’ Lyell's Principles of Geology, 9th edit., London, 1853, p. 198.
782. Dr. Whewell, comparing him with his great German contemporary, Werner, says, ‘In the German, considering him as a geologist, the ideal element predominated.’ … ‘Of a very different temper and character was William Smith. No literary cultivation of his youth awoke in him the speculative love of symmetry and system; but a singular clearness and precision of the classifying power, which he possessed as a native talent, was exercised and developed by exactly those geological facts among which his philosophical task lay.’ … ‘We see great vividness of thought and activity of mind, unfolding itself exactly in proportion to the facts with which it had to deal.’ … ‘He dates his attempts to discriminate and connect strata from the year 1790.’ Whewell's History of the Inductive Sciences, London, 1847, vol. iii. pp. 562–564.
783. ‘The execution of his map was completed in 1815, and remains a lasting monument of original talent and extraordinary perseverance; for he had explored the whole country on foot without the guidance of previous observers, or the aid of fellow-labourers, and had succeeded in throwing into natural divisions the whole complicated series of British rocks.’ Lyell's Principles of Geology, p. 58. Geological maps of parts of England had, however, been published before 1815. See Conybeare on Geology, in Second Report of the British Association, p. 373.
784. ‘A great body of new data were required; and the Geological Society of London, founded in 1807, conduced greatly to the attainment of this desirable end. To multiply and record observations, and patiently to await the result at some future period, was the object proposed by them; and it was their favourite maxim, that the time was not yet come for a general system of geology, but that all must be content for many years to be exclusively engaged in furnishing materials for future generalizations.’ Lyell's Principles of Geology, p. 59. Compare Richardson's Geology, 1851, p. 40.
785. Cuvier, in his Life of Werner, says (Biographie Universelle, vol. i. pp. 376, 377), ‘La connaissance des positions respectives des minéraux dans la croûte du globe, et ce que l'on peut en conclure relativement aux époques de leur origine, forment une autre branche de la science qu'il appelle Géognosie. Il en présenta les premières bases en 1787, dans un petit écrit intitulé “Classification et description des Montagnes.”’
786. Whewell's History of the Inductive Sciences, vol. iii. p. 567.
787. ‘Une mer universelle et tranquille dépose en grandes masses les roches primitives, roches nettement cristallisées, où domine d'abord la silice. Le granit fait la base de tout; au granit succède le gneiss, qui n'est qu'un granit commençant à se feuilleter.’ … ‘Des agitations intestines du liquide détruisent une partie de ces premiers dépôts; de nouvelles roches se forment de leurs débris réunis par des cimens. C'est parmi ces tempêtes que naît la vie.’ … ‘Les eaux, de nouveau tranquillisées, mais dont le contenu a changé, déposent des couches moins épaisses et plus variées, où les débris des corps vivans s'accumulent successivement dans un ordre non moins fixe que celui des roches qui les contiennent. Enfin, la dernière retraite des eaux répand sur le continent d'immenses alluvions de matières meubles, premiers sièges de la végétation, de la culture et de la sociabilité.’ Eloge de Werner, in Cuvier, Recueil des Elogés Historiques, vol. ii. pp. 321–323.
788. ‘If it be true that delivery be the first, second, and third requisite in a popular orator, it is no less certain that to travel is of first, second, and third importance to those who desire to originate just and comprehensive views concerning the structure of our globe. Now, Werner had not travelled to distant countries: he had merely explored a small portion of Germany, and conceived, and persuaded others to believe, that the whole surface of our planet, and all the mountain chains in the world, were made after the model of his own province.’ … ‘It now appears that he had misinterpreted many of the most important appearances even in the immediate neighbourhood of Freyberg. Thus, for example, within a day's journey of his school, the porphyry, called by him primitive, has been found not only to send forth veins, or dykes, through strata of the coal formation, but to overlie them in mass.’ Lyell's Principles of Geology, p. 47.
789. Though Hutton's Theory of the Earth was first published in 1788, the edition of 1795, which is the one I have used, contains a great number of additional illustrations of his views, and was evidently re-written. But the main features are the same; and we learn from his friend, Playfair, that ‘the great outline of his system’ was completed ‘several years’ before 1788. Life of Hutton, in Playfair's Works, vol. iv. p. 50, Edinburgh, 1822.
790. Kirwan appears to have been the first who called Hutton's theory ‘the Plutonic System.’ See Illustrations of the Huttonian Theory, in Playfair's Works, vol. i. p. 145. On the distinction between Neptunists and Plutonists, see the same work, pp. 504, 505.
791. ‘Has not only supplanted that of Werner, but has formed the foundation of the researches and writings of our most enlightened observers, and is justly regarded as the basis of all sound geology at the present day.’ Richardson's Geology, London, 1851, p. 38.
792. Hutton's Theory of the Earth, Edinb. 1795, vol. i. pp. 34, 41, 192, 290, 291, 593, vol. ii. pp. 236, 369, 378, 555.
793. ‘In his writings, and in those of his illustrator, Playfair, we find the germ of the metamorphic theory.’ Lyell's Manual of Geology, London, 1851, p. 92.
794. The shortest summary of this view is in his Theory of the Earth, Edin. 1795, vol. ii. pp. 556. ‘The doctrine, therefore, of our Theory is briefly this; that whatever may have been the operation of dissolving water, and the chemical action of it upon the materials accumulated at the bottom of the sea, the general solidity of that mass of earth, and the placing of it in the atmosphere above the surface of the sea, has been the immediate operation of fire or heat melting and expanding bodies.’
795. ‘Although Hutton had never explored any region of active volcanos, he had convinced himself that basalt and many other trap rocks were of igneous origin.’ Lyell's Principles of Geology, London, 1853, p. 51. To this I may add, that he wrote his work without having examined granite. He says (Theory of the Earth, vol. i. p. 214), ‘It is true, I met with it on my return by the east coast, when I just saw it, and no more, at Peterhead and Aberdeen; but that was all the granite I had ever seen when I wrote my Theory of the Earth. I have, since that time, seen it in different places; because I went on purpose to examine it, as I shall have occasion to describe in the course of this work.’ Hutton's theory of granite is noticed in Bakewell's Geology, London, 1838, p. 101: but Mr. Bakewell does not seem to be aware that the theory was formed before the observations were made.
796. Huttonian Theory, in Playfair, vol. i. pp. 38–40, 509, 510. Compare Playfair's Life of Hutton, p. 61.
797. Hence, the objections of Kirwan were invalid; because his argument against Hutton was ‘grounded on experiments, where that very separation of the volatile and fixed parts takes place, which it excluded in that hypothesis of subterraneous heat.’ Huttonian Theory, in Playfair, vol. i. p. 193, Edinb. 1822.
798. Hutton says (Theory of the Earth, Edinb. 1795, vol. i. p. 94), ‘The place of mineral operations is not on the surface of the earth; and we are not to limit nature with our imbecility, or estimate the powers of nature by the measure of our own.’ See also p. 159, ‘mineral operations proper to the lower regions of the earth.’ And p. 527, ‘The mineral operations of nature lie in a part of the globe which is necessarily inaccessible to man, and where the powers of nature act under very different conditions from those which we find take place in the only situation where we can live.’ Again, in vol. ii. p. 97, ‘The present Theory of the Earth holds for principle that the strata are consolidated in the mineral regions far beyond the reach of human observation.’ Similarly, vol. ii. p. 484, ‘we judge not of the progress of things from the actual operations of the surface.’
799. Hutton, however, did not believe that this could be done. ‘In the Theory of the Earth which was published, I was anxious to warn the reader against the notion that subterraneous heat and fusion could be compared with that which we induce by our chemical operations on mineral substances here upon the surface of the earth.’ Hutton's Theory of the Earth, vol. i. p. 251.
800. See, in the Life of Hutton, in Playfair's Works, vol. iv. p. 62 note, a curious remark on his indifference to experimental verification. Innumerable passages in his work indicate this tendency, and show his desire to reason immediately from general principles. Thus, in vol. i. p. 17, ‘Let us strictly examine our principles in order to avoid fallacy in our reasoning.’ … ‘We are now, in reasoning from principles, come to a point decisive of the question.’ vol. i. p. 177. ‘Let us now reason from our principles.’ vol. ii. p. 308. Hence, his constantly expressed contempt for experience; as in vol. ii. p. 367, where he says that we must ‘overcome those prejudices which contracted views of nature and magnified opinions of the experience of man may have begotten.’
801. Playfair (Life of Hutton, p. 64) says that it drew ‘their attention’ (i. e. the attention of ‘men of science’), ‘very slowly, so that several years elapsed before any one showed himself publicly concerned about it, either as an enemy or a friend.’ He adds, as one of the reasons of this, that it contained ‘too little detail of facts for a system which involved so much that was new, and opposite to the opinions generally received.’
802. The account of these experiments was read before the Royal Society of Edinburgh in 1805, and is printed in their Transactions, vol. vi. pp. 71–185, Edinb. 1812, 4to. The general result was (pp. 148, 149), ‘That a pressure of 52 atmospheres, or 1700 feet of sea, is capable of forming a limestone in a proper heat; That under 86 atmospheres, answering nearly to 3000 feet, or about half a mile, a complete marble may be formed; and lastly, That, with a pressure of 173 atmospheres, or 5700 feet, that is little more than one mile of sea, the carbonate of lime is made to undergo complete fusion, and to act powerfully on other earths.’ See also p. 160: ‘The carbonic acid of limestone cannot be constrained in heat by a pressure less than that of 1708 feet of sea.’ There is a short, and not very accurate, notice of these instructive experiments in Bakewell's Geology, London, 1838, pp. 249, 250.
803. As Sir James Hall says, ‘The truth of the most doubtful principle which Dr. Hutton has assumed, has thus been established by direct experiment.’ Transactions of the Royal Society of Edinburgh, vol. vi. p. 175.
804. See the remarks of Sir James Hall, in Transactions, vol. vi. pp. 74, 75. He observes that Hutton's ‘system, however, involves so many suppositions, apparently in contradiction to common experience, which meet us on the very threshold, that most men have hitherto been deterred from an investigation of its principles, and only a few individuals have justly appreciated its merits.’ … ‘I conceived that the chemical effects ascribed by him to compression, ought, in the first place, to be investigated.’ … ‘It occurred to me that this principle was susceptible of being established in a direct manner by experiment, and I urged him to make the attempt; but he always rejected this proposal, on account of the immensity of the natural agents, whose operation he supposed to lie far beyond the reach of our imitation; and he seemed to imagine that any such attempt must undoubtedly fail, and thus throw discredit on opinions, already sufficiently established, as he conceived, on other principles.’
805. It may be traced back, certainly to the beginning of the seventeenth century, and probably still higher. Yet the popular opinion seems to be correct, that Watt was its real inventor; though, of course, he could not have done what he did, without his predecessors. This, however, may be said of all the most eminent and successful men, as well as of the most ordinary men.
806. On the obligations of Watt to Black, compare Brougham's Life of Watt (Brougham's Works, vol. i. pp. 25, 36–38, edit. Glasgow, 1855), with Muirhead's Life of Watt, second edit. London, 1859, pp. 66, 83. At p. 301, Mr. Muirhead says of Watt, that ‘his principal inventions connected with the steam-engine, with all their prodigious results, were founded, as we have seen, on the attentive observation of great philosophical truths; and the economy of fuel, increase of productive power, and saving of animal labour, which gradually ensued, all originated in the sagacious and careful thought with which he investigated the nature and properties of heat.’ But whatever investigations Watt made into heat, he discovered no new law respecting it, or, at all events, no new law which is large enough to be noted in the history of thermotics, considered purely as a science, and apart from practical application. Mr. Muirhead, in his interesting work which I have just quoted, has published (pp. 484–486) some remarks made on the subject by Watt, several years after the death of Black, which, though perfectly fair and candid, show that Watt had a rather confused notion of the real difference between an invention and a discovery.
807. Mr. Muirhead, in his Life of Watt, pp. 301–370, seems to have put the priority of Watt beyond further doubt; though he is somewhat hard upon Cavendish, who, there can be little question, made the discovery for himself.
808. I would not wish to diminish one jot of the veneration in which the great name of Watt is justly held. But when I find the opinion of Dr. Withering, the botanist, quoted, to the effect that his ‘abilities and acquirements placed him next, if not superior, to Newton.’ (Muirhead's Life of Watt, p. 302), I cannot but protest against such indiscriminate eulogy, which would rank Watt in the same class as one of those godlike intellects of which the whole world has not produced a score, and which are entitled to be termed inspired, if ever human being was so. Another instance of this injudicious panegyric will be found in the same otherwise excellent work (Muirhead, pp. 324, 325), where we read that Watt's discovery that water consists of oxygen and hydrogen, was ‘the commencement of a new era, the dawn of a new day in physical inquiry, the real foundation of the new system of chemistry; nay, even a discovery “perhaps of greater importance than any single fact which human ingenuity has ascertained either before or since.”’
809. That there was no plagiarism on the part of Watt, we know from positive evidence; that there was none on the part of Cavendish, may be fairly presumed, both from the character of the man, and also from the fact that in the then state of chemical knowledge the discovery was imminent, and could not have been long delayed. It was antecedently probable that the composition of water would be ascertained by different persons at the same time, as we have seen in many other discoveries which have been simultaneously made, when the human mind, in that particular department of inquiry, had reached a certain point. We are too apt to suspect philosophers of stealing from each other, what their own abilities are sufficient to work out for themselves. It is, however, certain that Watt thought himself ill-treated by Cavendish. See Watt's Correspondence on the Composition of Water, London, 1846, pp. 48, 61.
810. On 26th November 1783, he writes: ‘For many years I have entertained an opinion that air was a modification of water; which was originally founded on the facts, that in most cases where air was actually made, which should be distinguished from those wherein it is only extricated from substances containing it in their pores, or otherwise united to them in the state of air, the substances were such as were known to contain water as one of their constituent parts, yet no water was obtained in the processes, except what was known to be only loosely connected with them, such as the water of the crystallization of salts. This opinion arose from a discovery that the latent heat contained in steam diminished, in proportion as the sensible heat of the water from which it was produced, increased; or, in other words, that the latent heat of steam was less when it was produced under a greater pressure, or in a more dense state, and greater when it was produced under a less pressure, or in a less dense state; which led me to conclude, that when a very great degree of heat was necessary for the production of the steam, the latent heat would be wholly changed into sensible heat; and that, in such cases, the steam itself might suffer some remarkable change. I now abandon this opinion, in so far as relates to the change of water into air, as I think that may be accounted for on better principles.’ See this remarkable passage, which is quite decisive as to the real history of Watt's discovery, in Correspondence of James Watt on the Composition of Water, London, 1846, pp. 84, 85. Compare p. cxxiv. and p. 248 note.
811. In the paper which he communicated to the Royal Society, announcing his discovery, he, well knowing the empirical character of the English mind, apologizes for this; and says, ‘I feel much reluctance to lay my thoughts on these subjects before the public in their present indigested state, and without having been able to bring them to the test of such experiments as would confirm or refute them.’ Watt's Correspondence on the Discovery of the Composition of Water, pp. 77, 78. Eleven months earlier, that is in December 1782, he writes (Ibid. p. 4): ‘Dr. Priestley has made a most surprising discovery, which seems to confirm my theory of water's undergoing some very remarkable change at the point where all its latent heat would be changed into sensible heat.’
812. ‘He’ (i. e. Cavendish) ‘here omits entirely the consideration of latent heat; an omission which he even attempts to justify, in one of the passages interpolated by Blagden. But it is well known to every one acquainted with the first principles of chemical science, even as it was taught in the days of Black, and it was indisputably familiar to Mr. Watt, that no aëriform fluid can be converted into a liquid, nor any liquid into a solid, without tho evolution of heat, previously latent. This essential part of the process, Mr. Cavendish's theory does not embrace; but without it, no theory on the subject can be complete; and it will presently be seen, that Mr. Watt took it fully into account.’ Muirhead's Life of Watt, p. 315.
813. ‘Cavendish and Watt both discovered the composition of water. Cavendish established the facts; Watt the idea.’ … ‘The attaching too high a value to the mere facts, is often a sign of a want of ideas.’ Liebig's Letters on Chemistry, London, 1851, p. 48. The last sentence of this illustrious philosopher, which I have put in italics, should be well pondered in England. If I had my way, it should be engraved in letters of gold over the portals of the Royal Society and of the Royal Institution.