History of Civilization in England, Vol. 3 of 3

756

The theory of the indestructibility of force has been applied to the law of gravitation by Professor Faraday, in his Discourse on the Conservation of Force, 1857; an essay full of thought and power, and which should be carefully studied by every one who wishes to understand the direction which the highest speculations of physical science are now taking. I will quote only one passage from the opening, to give the reader an idea of its general scope, irrespective of the more special question of gravitation. ‘The progress of the strict science of modern times has tended more and more to produce the conviction that force can neither be created nor destroyed; and to render daily more manifest the value of the knowledge of that truth in experimental research.’ … ‘Agreeing with those who admit the conservation of force to be a principle in physics, as large and sure as that of the indestructibility of matter, or the invariability of gravity, I think that no particular idea of force has a right to unlimited or unqualified acceptance, that does not include assent to it.’

757

As an illustration of this doctrine, I cannot do better than quote the following passage from one of the most suggestive and clearly reasoned books which has been written in this century by an English physicist: ‘Wave your hand; the motion which has apparently ceased, is taken up by the air, from the air by the walls of the room, &c., and so by direct and reacting waves, continually comminuted, but never destroyed. It is true that, at a certain point, we lose all means of detecting the motion, from its minute subdivision, which defies our most delicate means of appreciation, but we can indefinitely extend our power of detecting it accordingly as we confine its direction, or increase the delicacy of our examination. Thus, if the hand be moved in unconfined air, the motion of the air would not be sensible to a person at a few feet distant; but if a piston of the same extent of surface as the hand be moved with the same rapidity in a tube, the blast of air may be distinctly felt at several yards' distance. There is no greater absolute amount of motion in the air in the second than in the first case, but its direction is restrained, so as to make its means of detection more facile. By carrying on this restraint, as in the air-gun, we get a power of detecting the motion, and of moving other bodies at far greater distances. The puff of air which would in the air-gun project a bullet a quarter of a mile, if allowed to escape without its direction being restrained, as by the bursting of a bladder, would not be perceptible at a yard's distance, though the same absolute amount of motion be impressed on the surrounding air.’ Grove's Correlation of Physical Forces, London, 1855, pp. 24, 25. In a work now issuing from the press, and still unfinished, it is suggested, with considerable plausibility, that Persistence of Force would be a more accurate expression than Conservation of Force. See Mr. Herbert Spencer's First Principles, London, 1861, p. 251. The title of this book gives an inadequate notion of the importance of the subjects with which it deals, and of the reach and subtlety of thought which characterize it. Though some of the generalizations appear to me rather premature, no well-instructed and disciplined intellect can consider them without admiration of the remarkable powers displayed by their author.

758

He was appointed professor in 1756; and ‘it was during his residence in Glasgow, between the years 1759 and 1763, that he brought to maturity those speculations concerning the combination of heat with matter, which had frequently occupied a portion of his thoughts.’ Thomson's History of Chemistry, vol. i. pp. 319, 320.

759

Black's Lectures on Chemistry, vol. i. pp. 116, 117; and in various places. Dr. Robison, the editor of these Lectures, says, p. 513, ‘Nothing could be more simple than his doctrines of latent heat. The experience of more than a century had made us consider the thermometer as a sure and accurate indicator of heat, and of all its variations. We had learned to distrust all others. Yet, in the liquefaction and vaporization of bodies, we had proofs uncontrovertible of the entrance of heat into the bodies. And we could, by suitable processes, get it out of them again. Dr. Black said that it was concealed in them, —latent, – it was as much concealed as carbonic acid is in marble, or water in zeolite, – it was concealed till Dr. Black detected it. He called it Latent Heat. He did not mean by this term that it was a different kind of heat from the heat which expanded bodies, but merely that it was concealed from our sense of heat, and from the thermometer.’ See also p. xxxvii.: ‘Philosophers had long been accustomed to consider the thermometer as the surest means for detecting the presence of heat or fire in bodies, and they distrusted all others.’

760

‘Fluidity is the consequence of a certain combination of calorific matter with the substance of solid bodies,’ &c. Black's Lectures, vol. i. p. 133. Compare p. 192, and the remarks in Turner's Chemistry, 1847, vol. i. p. 31, on Black's views of the ‘chemical combination’ of heat. Among the backward chemists, we still find traces of the idea of heat obeying chemical laws.

761

‘So much was he convinced of this, that he taught the doctrine in his lectures in 1761, before he had made a single experiment on the subject.’ … ‘The requisite experiments were first attempted by Dr. Black in 1764.’ Thomson's History of Chemistry, vol. i. p. 324. See also pp. 319, 320; and on the history of the idea in Black's mind as early as the year 1754, see the interesting extracts from his note-books in Robison's appendix to Black's Lectures, vol. i pp. 525, 526.

The statement of Dr. Thomson refers to the completion, or last stage, of the discovery, namely the vaporific combination of heat. But from a letter which Black wrote to Watt in 1780 (Muirhead's Life of Watt, London, 1859, p. 303), it appears that Thomson has even understated the question, and that Black, instead of first teaching his theory in 1761, taught it three years earlier, that is, six years before the decisive experiments were made. ‘I began,’ writes Black, ‘to give the doctrine of latent heat in my lectures at Glasgow in the winter 1757–58, which, I believe, was the first winter of my lecturing there; or if I did not give it that winter, I certainly gave it in the 1758–59; and I have delivered it every year since that time in my winter lectures, which I continued to give at Glasgow until winter 1766–67, when I began to lecture in Edinburgh.’

762

And he distinctly states that, even in other matters, when he did make experiments, their object was to confirm theory, and not to suggest it. Thus, to give one of many instances, in his Lectures, vol. i. p. 354, he says, respecting salts, ‘When we examine the solidity of this reasoning by an experiment, we have the pleasure to find facts agree exactly with the theory.’

763

See a good summary of this idea in Black's Lectures on Chemistry, vol. i. p. 118. Contrasting his theory of heat with that previously received, he says, ‘But, were the ice and snow to melt as suddenly as they must necessarily do, were the former opinion of the action of heat in melting them well founded, the torrents and inundations would be incomparably more irresistible and dreadful. They would tear up and sweep away every thing, and that so suddenly, that mankind should have great difficulty to escape from their ravages.’

764

‘Dr. Black quickly perceived the vast importance of this discovery; and took a pleasure in laying before his students a view of the extensive and beneficial effects of this habitude of heat in the economy of nature. He made them remark how, by this means, there was accumulated, during the summer season, a vast magazine of heat, which, by gradually emerging, during congelation, from the water which covers the face of the earth, serves to temper the deadly cold of winter. Were it not for this quantity of heat, amounting to 145 degrees, which emerges from every particle of water as it freezes, and which diffuses itself through the atmosphere, the sun would no sooner go a few degrees to the south of the equator, than we should feel all the horrors of winter.’ Robison's Preface to Black's Lectures, vol. i. p. xxxviii.

765

As I am writing an account of Black's views, and not a criticism of them, I shall give them, without comment, in his own words, and in the words of one of his pupils. ‘Here we can also trace another magnificent train of changes, which are nicely accommodated to the wants of the inhabitants of this globe. In the equatorial regions, the oppressive heat of the sun is prevented from a destructive accumulation by copious evaporation. The waters, stored with their vaporific heat, are thus carried aloft into the atmosphere, till the rarest of the vapour reaches the very cold regions of the air, which immediately forms a small portion of it into a fleecy cloud. This also further tempers the scorching heat by its opacity, performing the acceptable office of a screen. From thence the clouds are carried to the inland countries, to form the sources in the mountains, which are to supply the numberless streams that water the fields. And, by the steady operation of causes, which are tolerably uniform, the greater part of the vapours pass on to the circumpolar regions, there to descend in rains and dews; and in this beneficent conversion into rain, by the cold of those regions, each particle of steam gives up the 700 or 800 degrees of heat which were latent in it. These are immediately diffused, and soften the rigour of those less comfortable climates.’ … ‘I am persuaded that the heat absorbed in spontaneous evaporation greatly contributes to enable animals to bear the heat of the tropical climates, where the thermometer frequently continues to show the temperature of the human body. Such heats, indeed, are barely supportable, and enervate the animal, making it lazy and indolent, indulging in the most relaxed postures, and avoiding every exertion of body or mind. The inhabitants are induced to drink large draughts of diluting liquors, which transude through their pores most copiously, carrying off with them a vast deal of this troublesome and exhausting heat. There is in the body itself a continual laboratory, or manufacture of heat, and, were the surrounding air of such a temperature as not to carry it off, it would soon accumulate so as to destroy life. The excessive perspiration, supplied by diluting draughts, performs the same office as the cold air without the tropics, in guarding us from this fatal accumulation.’ Black's Lectures, vol. i. pp. xlvi. 214.

766

See his strong protest against the notion that heat is ever destroyed, in his Lectures, vol. i. pp. 125, 126, 164, 165.

767

They were published after his death from such scanty materials, that their editor, Dr. Robison, says (Preface to Black's Lectures, vol. i. p. x.): ‘When I then entered seriously on the task, I found that the notes were (with the exception of perhaps a score of lectures) in the same imperfect condition that they had been in from the beginning, consisting entirely of single leaves of paper, in octavo, full of erasions, interlinings, and alterations of every kind; so that, in many places, it was not very certain which of several notes was to be chosen.’

768

‘On the other hand, were the heat which at present cherishes and enlivens this globe, allowed to increase beyond the bounds at present prescribed to it; beside the destruction of all animal and vegetable life, which would be the immediate and inevitable consequence, the water would lose its present form, and assume that of an elastic vapour like air; the solid parts of the globe would be melted and confounded together, or mixed with the air and water in smoke and vapour; and nature would return to the original chaos.’ Black's Lectures, vol. i. pp. 246, 247.

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.