RELATIONS TO OTHER SCIENCES. 237 to experiment; whereas, they now have a character of rationality which fits them for purposes of prevision. From the complexity of physical phenomena, however, the difficulty of the mathematical application is great. In some, a j^art of the essential conditions of the problem must be thrown out, to admit of its transformation into a mathematical question; and hence the necessity for reserve in the employment of analysis. The art of combining analysis and experiment, without subordinating the one to the other, is still almost unknown. It constitutes the last advance of the true method of physical study; and it will be developed when physicists, and not geometers, conduct the anal}'tical process, and not till then.
Having seen what is the object of Physics, Encyclopedi- and what the means of investigation, we cal Rank of have next to fix its position in tlie scientific Pkysics. hierarchy.
The phenomena of Physics are more complicated than those of Astronomy; and Astronomy is the scientific basis and model of Physics, which cannot be effectually studied otherwise than through the study of the more simple and general science. In this, we individually follow the course of our race. It was by Astronomy that the t? i +• positive spirit was introduced into natural Astronomv philosophy, after it had been sufficiently developed by purely mathematical investigations. Our individual education is in analogy with this: for we have learned from astronomy what is the real meaning of the explanation of a phenomenon, without any imjjracticable inquiry about its cause, first or final, or its mode of produc- tion. Physics should, more than the other natural sciences, follow closely upon astronomy, because, after astronomy, its phenomena are less complex than any.
Besides these reasons belonging to Method, there is the grand consideration that the theories of astronomy afford the only data for the study of terrestrial physics. Our position in the solar system, and the motions, form, size, and equilibrium of the mass of our world among the other planets, must be known before we can understand the phenomena going on at its surface. What could we make of weight, for instance, or of the tides, without the data 238 POSITIVE PHILOSOPHY.
afforded by astronomical science? These phenomena indeed make the transition from astronomy to physics almost insensible. In this way Physics is iudi- Matheinatics i^^ctly connected with Mathematics. There is also a direct connection, as some physical phenomena have a geometrical and mechanical character, — as much as those of astronomy, though under a great com- plication of the circumstances. The abstract laws of space and motion must j^revail as much in the one science as in the other. If the relation is thus unquestionable in the doctrine, it is not less so in the spirit and method which we must bring to the study of physics. It must be ever re- membered that the true positive spirit first came forth from the pare sources of mathematical science; and it is only the mind that has imbibed it there, and which has been face to face with the lucid truths of geometry and mechanics, that can bring into full action its natural posi- tivity, and apply it in bringing the most complex studies into the reality of demonstration. No other discipline can fitly prepare the intellectual organ. We might further say that, as geometrical ideas are more clear and fvmda- mental than mechanical ideas, the former are more neces- sary, in an educational sense, to physicists than the latter, though the iise of mechanical ideas is the more immediate and extended in jjhysical science. Thus we see how we must conclude that the education of physicists must be more comijlicated than that of astronomers. Both have need of the same mathematical basis, and physicists m.ust also have studied astronomy, at least in a general way. And this, again, assigns the position of their science.
Its rank is equally clear, if we look in the opposite direc- tion,— at the sciences which come after it.
It can hardly be by accident that, in all the rest languages of thinking peoj^les, the word which originally indicated the study of the whole of nature should have become the name of the particular science we are now considering. Astronomy is, in fact, an emanation from mathematics. Every other natural science was once comprehended under the term Physics; and that to which it is now restricted must be supreme over the rest. Its relation to the rest is just this: that it investi- RELATION TO HUMAN PROGRESS. 239 gates the general properties common to all bodies; that is, the fundamental constitution of matter; while the other sciences exhibit the modifications of those j^roj^erties peculiar to each: and the study of those properties in the general must, of course, precede that of their particular cases. In regard to Physiology, for instance, it is clear that organized bodies are subject to the general laws of matter, those laws being modified in their manifestations by the characteristic circumstances of the state of Life. The same is the case with Chemistry, Without admitting the questionable hypothesis under which some eminent men of our time refer all chemical j^henomena to purely physical action, it is yet evident that the concurrence of physical influences is indispensable to every chemical act. What could we make of any phenomenon of composition or decomposition, if we left out all data of weight, heat, electricity, etc.? And how could we estimate the chemical power of these various agents without first knowing the laws of the general influ- ence proper to each? Chemistry is closely dependent on Physics; while Physics is wholly independent of Chemisti-y.
As for the direct operation of this science Relation to on the human intellect, it is less marked than human pro- that of the two natural sciences which occupy gi'e.ss. the extremities of the scale, — astronomy and physiology, — which immediately contemplate the two great objects of human interest, — the Universe and Man: but one striking fact with regard to Physics is that it has been the great battle-ground between the old theological and metaphysical spirit and the positive philosophy. In Astronomy the positive philosophy took possession, and triumphed almost without opposition, except about the earth's motion; while in the domain of Physics the conflict has gone on for cen- turies; a circumstance attributable to the imperfection of physical, in comparison with astronomical science.
With this science begins the exhibition of Human power human power in modifying phenomena. In of modifying Astronomy, human intervention was out of plienomena. the question: in Physics it begins; and we shall see how it becomes more powerful as we descend the scale. This power counterbalances that of exact prevision which we have in astronomy, through its extreme simplicity. The 240 POSITIVE PHILOSOPHY.
one power or the other, — the power of foreseeing or of modifying, — is necessary to our outgrowth of theological philosophy. Our j^revision disproves the notion that phe- nomena proceed from a supernatural will, which is the same thing as calling them variable: and our ability to modify them shows that the powers under which they proceed are subordinated to our own. The first is the higher order of proof; but both are complete in their way, and certain to command, sooner or later, universal assent. The proof which Franklin afforded of human control over the lightning destroyed the religious terror of thunder as effectually as the superstition about comets was destroyed by the j^revision of their return; though the experiments by which Franklin established the identity of the lightning with the common electric discharge could be decisive only with physicists, while the generality of men could under- stand how the return of comets was foreseen. As the opposition between the theological and the positive philo- sophies becomes less simply evident, our power of interven- tion becomes more varied and extended; the amount of proof yielded in the two cases being equal in the eyes of men in general, though not strictly equivalent.
„...In regard to the speculative rank of Phynerfect ^'^^^' ^^ ^^ clear that it does not admit of prevision to any extent at all comparable to that of astronomy, because it consists of numerous branches, scarcely at all connected with each other, and concurring only in a feeble and doubtful way in its chief phenomena. We can therefore see only a little way forward; often scarcely beyond the experiment in hand: but we shall see its speculative superiority to the sciences which come after it, when, in studying chemistry and physiology, we find another kind of incoherence existing among their pheno- mena, making prevision more imperfect still. The greal distinction of Physics is that which has been referred to before, — that it instructs us in the art of Experiment. Philosophers must ascend to this source of experimentation, whatever their special objects may be, to learn what ai'e the sjiirit and conditions of true experimentation, and what the necessary precautions. Each of the sciences in the scale presents, besides the characters of the positive method THE SCIENTIFIC USE OF HYPOTHESIS. 241 which are coram oii to them all, some indication ajjpropriate to itself, which ought to be studied at its Characteris- source, to be duly appreciated. Mathema- tics of each tical science exhibits the elementary con- science, ditions of positivity: astronomy determines the ti'ue stud}- of Nature: physics teaches us the theory of experimen- tation: chemistry offers us the art of nomenclature: and physiology discloses the true theory of classification.
I have deferred till now what I have to offer on the important subject of the rational construction and scientific use of hypotheses, regarded as a powerful and indispensable auxiliary to our study of nature. It is in the region of astronomy that I must take my hypothesis stand in discussing this subject, though it was not necessary to advert to it while we were surveying that region. Hypothesis is abundantly emj^loyed in astro- nomy; but there it may be said to prescribe the conditions of its own use, — so simple are the phenomena in question there. From thence do I think it necessary to derive, therefore, our conceptions of the character and rules of this valuable resource, in order to its employment in the other departments of natural philosophy.
There are only two general methods by which we can get at the law of any phenomenon, — the immediate analysis of the course of the phenomenon, or its relation to some more extended law already established; in other words, by induc- tion or deduction. Neither of these methods would helj) us, even in regard to the simplest phenomena, if we did not begin by anticipating the results, by making a pro- visional supposition, altogether conjectural in the first instance, with regard to some of the very notions which are the object of the inquiry. Hence the necessary introduc- tion of hypotheses into natural philosophy. The method of approximation employed by geometers first suggested the idea; and without it all discovery of natural laws would be impossible in cases of any degree of complexity; and in all, very slow. But the employment of this instrument must always be subjected to one condition, the neglect of which would impede the development of real knowledge. This condition is to imagine such hypotheses Necessarv cou- ouly as admit, by their nature, of a positive dition.
I. R and inevitable verification at some future time, — the pre- cision of this verification being proportioned to what we can learn of the corresponding phenomena. In other words, philosophical hypotheses must always have the character of simple anticipations of what we might know at once, by experiment and reasoning, if the circumstances of the problem had been moi'e favourable than they are. Provided this rule be scrupulously observed, hypo- theses may evidently be employee! without danger, as often as they are needed, or rationally desired. It is only sub- stituting an indirect for a direct investigation, when the latter is impossible or too difficult. But if the two are not employed on the same general subject, and if we try to reach by hypothesis what is inaccessible to observation and reasoning, the fundamental condition is violated, and hypothesis, wandering out of the field of science, merely leads us astray. Our study of nature is restricted to the analysis of phenomena in order to discover their laws; that is, their constant relations of succession or similitvide; and (•an have nothing to do with their vature, or their cause, first or final, or the mode of their production. Every hypothesis which strays beyond the domain of the positive can merely occasion interminable discussions, by 2:>retending to pronounce on questions which our understandings are incompetent to decide. — Every man of science admits this rule, in its simple statement; but it cannot be practically understood, — so often as it is violated, and to such a degree as to alter the whole character of Physics. The use of conjecture is to fill up provisionally the intervals left here and there by reality; but practically we find the two mate- rials entirely separated, and the real subordinated to the (Conjectural. It is necessary, therefore, to ascertain and explain the actual state of the question with regard to Physics.
The hyjiotheses employed by physical in- liTDotliesis^ ^ quirers in our day are of two classes: the first, a very small class, relate simply to the laws of phenomena: the other, and larger class, aim at de- termining the general agents to which different kinds of natural effects may be referred. Now, according to the rule just laid down, the first kind alone are admissible: THE TWO CLASSES OF HYPOTHESES. 243 the second have au anti-scientific character, are chimerical, and can do nothiu^; but hinder the progress of science.
In Astronomy, the first class only is in use, because the science has a wholly positive indispensable character. A fact is obscure; or a law is unknown: we proceed to form a hypothesis, in agreement, as far as possible, with the wdiole of the data we are in possession of; and the science, thus left free to develop itself, always ends by disclosing new observable conse- quences, tending to confirm or invalidate, indisputably, the primitive supposition. We have before noticed frequent and happy examples of this method of discovering the primary truths of astronomy. But, since the establish- ment of the law of gravitation, geometers and astronomers have put away all their fancies of chimerical fluids causing planetary motions; or have, at least, indulged in them merely as a matter of personal taste, and not of scientific investigation. It would be well if, in a study so much more difficult as Physics, philosophers would imitate the astronomers. It would be well if they would confine their hypotheses to the yet unknown chimerical circumstances of phenomena, or their yet hidden laws, and would entirely let alone their mode of production, which is altogether beyond the limit of our faculties. What scientific use can there be in fantastic notions about fluids and imaginary ethers, which are to account for phenomena of heat, light, electricity and magnetism? Such a mixture of facts and dreams can only vitiate the essential ideas of physics, cause endless controversy, and involv.e the science itself in the disgust which the wise mi;st feel at such proceedings. These fluids are supposed to be invisible, intangible, even im- ponderable, and to be inseparable from the substances which they actuate. Their very definition shows them to have no place in real science; for the question of their existence is not a subject for judgment: it can no more be denied then affirmed: our reason has no grasp of them at all. Those who, in our day, believe in caloric, in a lumi- nous ether, or electric fluids, have no right to depise the elementary spirits of Paracelsus, or to refuse to admit angels and genii. We find them spurning Lamarck's notion 244 POSITIVE PHILOSOPHY.
of a resonant fluid; but the misfortune of tliis hypothesis was that it came too late, — long after the establishment of acoustics. If it had been put forth as early in the days of science as the hypotheses about heat, light, and electricity, this resonant fluid would no doubt have prosjjered as well as the rest. Without going into the history of more of these baseless inquiries, it is enough to point out that they are irreconcileable with each other; and when superficial minds witness the ease with which they destroy each other, they naturally conclude the whole science to be arbitrary, consisting more in futile discussion than in anything else. Each sect or philosopher can show how untenable is the hypothesis of another, but cannot establish his own; and it would generally be easy to devise a third which might agree with both. It is true, physicists are now eager to declare that they do not attribute any intrinsic reality to these hypotheses; and that they countenance them merely as indispensable means for facilitating the conception and combination of phenomena. But we see here the working of an incomj^lete jiositivity, which feels the inanity of such systems, and yet dares not surrender theni. But besides that it is scarcely possible to employ a fictitious instrument as a reality without at times falling into the delusion of its reality, what rational ground is there for proceeding in such a way, when we have before us the procedure and achievements of astronomical science, for a pattern and a promise? These hyj:)Otheses exjjlain nothing. For instance, the expansion of bodies by heat is not explained, — that is, cleared up, — by the notion of an imaginary fluid interposed between the molecules, which tends constantly to enlarge their intervals; for we still have to learn how this sup- posed fluid came by its spontaneous elasticity, which is, if anything, more unintelligible than the primitive fact. And so on, through the whole range. These hypotheses clear away no difficulties, but only make new ones, while they divert our attention from the true object of our inquiries. As for the plea that habit has so taken hold of the minds of inquirers, that they would be adrift if de- prived of all their moorings at once, and that their language must be superseded by a wholly new one, I think this kind of difficulty is very much (exaggerated. We have seen.
HISTORY OF THK SECOND CLASS. 245 within half a century, how often men have contrived to pass from some physical systems to their opposites without being much hindered by obstacles of language. There would be scarcely more difficulty in casting aside futile hypotheses; and we might, as we see by existing examples, gradually substitute the real and permanent meaning of scientific terms for the fanciful and variable interpre- tation.
These fluids are nothing more than the old.
entities materiahzed. Whichever way we secoiuPdass'^ look at it, what is heat apart from the warm body, light apart from the luminous body, — electricity apart from the electric body? Are they not pure entities, like thought apart from the thinking body, and digestion apart from the digesting body? Here we have, instead of abstract beings, imaginary fluids deprived, by their very definition, of all material qualities, so that we cannot even suppose in them the limit of the most rarefied gas. If the descent of these from the old entities be not recognized, what filiation of ideas can ever be admitted? The essential character of metaphysical conceptions is to attribute to properties an existence separate from the substance which manifests them. Wliat does it matter whether we call these abstractions souls or fluids? The origin is always the same; and it is connected with that inquisition into the essence of things which always characterizes the infancy of the human mind, occasioning, first, the conception of gods, which grew into that of souls, which became in time imaginary fluids. In all positive science, our understand- ings, unable to pass abrujitly from the metaphysical to the positive stage, have travelled through this transition state of development. Metaphysics itself is the transition stage from theology to positive science; but a secondary tran- sition is also necessary, as we see by the fact; a transition from metaphysical to positive conceptions. The mathe- maticians and astronomers have attained the positive basis. The physicists, the chemists, the physiologists, and the social philosophers, are now in the last period of tran- sition; the physical inquirers, ready to pass up to the level of the astronomers and geometers, and all the others held back for a while by the complexity of their respective sub- 246 POSITIVE PHILOSOPHV.
jects; as we shall see hereafter. This bastard positivism was the way out of the old metaphysical couditiou, in which men would, but for it, have been imprisoned to this day. Nascent science first humoured the constitutional need, and then led us on by offering to our minds, in the place of the old scholastic entities, new entities, more tangible, which must by their nature introduce into our studies the contemplation of phenomena and their laws, restricting us to these more and more. This seems to have been the important temporary use of this system of hypo- theses; to enable us to jjass from the metaphysical to the positive stage.
J., _ Astronomy has not been exempted from this transition state, anymore than the other sciences; but it was over so long ago that it is forgotten, — so few are those who are interested in the history of philosophy! If we look back to the action of the human mind in the seventeenth century, we shall see how geo- meters and astronomers were preoccupied with hypotheses of the kind we are considering. There is no better example of them than that famous conception, the Vortices of Descartes; for it presents cleai'ly the three stages of exis- tence common to them all; the creation of the hypothesis, its temporary use, and its rejection when its purpose is answered. These vortices, so ridiculed by men who believe in caloric, ether, and electric fluids, helj^ed us to a sound philosophy by introducing the idea of mechanism, where even Kepler had imagined only the incomprehensible action of souls and genii. When the discussion had attained the firm ground of Celestial Mechanics, founded upon the Newtonian theory, the influence of the Cartesian hypothesis ceased to be progressive, and became retrograde. To the last, the Cartesian philosophers insisted, in arguments as plausible as those of our existing physicists, that it was impossible to philosophize without such a hypothesis.
They were answered in the only effe(;tual way, by philo- sophizing in another mode: and the vortices were heard of no more when geometers and astronomers apprehended the true object of scientific studies. The Cartesian hypo- thesis contributed to the education of the human mind by leadinar it to see that we have nothing to do with the APPLICATION IN PHYSICS. 247 primitive agents, or mode of production of phenomena, but only with their laws. If, in the other sciences, we have, as their professors assert, reached the stage of posi- tivity, hypotheses like that of the vortices may be dismissed, as no longer needed to bring us out of the metaphysical state. As soon as they are needless, they become per- nicious.
The transition has been obvious elsewhere j p, ^.- than in astronomy. It has taken place in the most advanced departments of Physics; and espe- cially with regard to Weight. There was scarcely a philo- sopher, even long after Galileo's time, who had not some system to offer about the causes of the fall of bodies. At that time, such hypotheses appeared the only method of studying weight; but who hears of them now? Acoustics was emancipated about the same time. The labours of Fourier will evidently release thermology; and then there will remain only the study of light and of electricity; ' and no reason can be assigned for their exclusion from the general rule. The question will be regarded as settled henceforward by all who believe that the historical develop- ment of the human mind is subject to natural laws, deter- minate and uniform; and such will admit, as the princi])le of the true theory of hypotheses, that every scientific- hypo- thesis, to be a matter of judgment, must relate exclusively to the laws of phenomena, and never to their mode of production.