tions, sufficient to indicate the possi- [take the place of, those which arise from the separate agency of the same causes: the laws of these new effects being again susceptible of composition to an indefinite extent, like the laws which they superseded. bility of ultimately proceeding farther. We can predicate some common properties of the kind of compounds which result from the combination in each of the small number of possible proportions, of any acid whatever with any base. We have also the curious law, discovered § 3. That effects are proportional by Berthollet, that two soluble salts to their causes is laid down by some mutually decompose one another when-writers as an axiom in the theory of ever the new combinations which re- causation; and great use is sometimes sult produce an insoluble compound, made of this principle in reasonings or one less soluble than the two for- respecting the laws of nature, though mer. Another uniformity is that it is encumbered with many difficalled the law of isomorphism; the culties and apparent exceptions, which identity of the crystalline forms of much ingenuity has been expended in substances which possess in common showing not to be real ones. This certain peculiarities of chemical com- proposition, in so far as it is true, position.* Thus it appears that even enters as a particular case into the heteropathic laws, such laws of com- general principle of the Composition bined agency as are not compounded of Causes; the causes compounded of the laws of the separate agencies, being, in this instance, homogeneous; are yet, at least in some cases, derived in which case, if in any, their joint from them according to a fixed prin- effect might be expected to be identiciple. There may, therefore, be laws cal with the sum of their separate of the generation of laws from others effects. If a force equal to one dissimilar to them; and in chemistry, hundredweight will raise a certain these undiscovered laws of the depend- body along an inclined plane, a force ence of the properties of the compound equal to two hundredweight will raise on the properties of its elements, may, two bodies exactly similar, and thus together with the laws of the elements the effect is proportional to the cause. themselves, furnish the premises by But does not a force equal to two which the science is perhaps destined hundredweight actually contain in one day to be rendered deductive. itself two forces each equal to one hundredweight, which, if employed apart, would separately raise the two bodies in question? The fact, therefore, that when exerted jointly they raise both bodies at once, results from the Composition of Causes, and is a mere instance of the general fact that mechanical forces are subject to the law of Composition. And so in every other case which can be supposed. For the doctrine of the proportionality of effects to their causes cannot of course be applicable to cases in which the augmentation of the cause alters the kind of effect; that is, in which the surplus quantity superadded to the cause does not become compounded with it, but the two together generate an altogether new phenomenon. Suppose that the application of a certain It would seem, therefore, that there is no class of phenomena in which the Composition of Causes does not obtain: that, as a general rule, causes in combination produce exactly the same effects as when acting singly; but that this rule, though general, is not universal that in some instances, at some particular points in the transition from separate to united action, the laws change, and an entirely new set of effects are either added to, or * Professor Bain adds several other wellestablished chemical generalisations: "The laws that simple substances exhibit the strongest affinities; that compounds are more fusible than their elements; that combination tends to a lower state of matter from gas down to solid;" and some general propositions concerning the circumstances which facilitate or resist chemical combination (Logic, ii. 254). quantity of heat to a body merely in- resulting from, and corollaries capcreases its bulk, that a double quantity able of being deduced from, such melts it, and a triple quantity decom- laws. If we could determine what poses it these three effects being causes are correctly assigned to what heterogeneous, no ratio, whether cor-effects, and what effects to what responding or not to that of the causes, we should be virtually acquantities of heat applied, can be quainted with the whole course of established between them. Thus the nature. All those uniformities which supposed axiom of the proportionality are mere results of causation might of effects to their causes fails at the then be explained and accounted for; precise point where the principle of and every individual fact or event the Composition of Causes also fails, might be predicted, provided we had viz. where the concurrence of causes the requisite data, that is, the requisite is such as to determine a change in knowledge of the circumstances which, the properties of the body generally, in the particular instance, preceded it. and render it subject to new laws, more or less dissimilar to those to which it conformed in its previous state. The recognition, therefore, of any such law of proportionality, is superseded by the more comprehensive principle, in which as much of it as is true is implicitly asserted. * The general remarks on causation, which seemed necessary as an introduction to the theory of the inductive process, may here terminate. That process is essentially an inquiry into cases of causation. All the uniformities which exist in the succession of phenomena, and most of the uniformities in their co-existence, are either, as we have seen, themselves laws of causation, or consequences * Professor Bain (Logic, ii. 39) points out a class of cases, other than that spoken of in the text, which he thinks must be regarded as an exception to the Composition of Causes. "Causes that merely make good the collocation for bringing a prime mover into action, or that release a potential force, do not follow any such rule. One man may direct a gun upon a fort as well as three: two sparks are not more effectual than one in exploding a barrel of gunpowder. In medicine there is a certain dose that answers the end, and adding to it does no more good." To ascertain, therefore, what are the laws of causation which exist in nature; to determine the effect of every cause, and the causes of all effects, is the main business of Induction; and to point out how this is done is the chief object of Inductive Logic. CHAPTER VII. OF OBSERVATION AND EXPERIMENT. § 1. IT results from the preceding exposition, that the process of ascertaining what consequents in nature are invariably connected with what antecedents, or, in other words, what phenomena are related to each as quickly as one, though one is enough. Two sparks put two sets of particles of the gunpowder into the state of intestine motion which make them explode, though one is sufficient. It is the collocation itself that does not, by being doubled, always double the effect; because in many cases a certain collocation, once obtained, is all that is required for the production of the whole amount of effect which can be produced at all at the given time and place. Doubling the collocation with difference of time and place, as by pointing two guns, or exploding a second barrel after the first, does double the effect. This remark applies still more to Mr. Bain's third example, that of a double dose of medicine; for à double dose of an aperient does purge more vio I am not sure that these cases are really exceptions. The law of Composition of Causes, I think, is really fulfilled, and the appearance to the contrary is produced by attending to the remote instead of the im-lently, and a double dose of laudanum does mediate effect of the causes. In the cases mentioned, the immediate effect of the causes in action is a collocation, and the duplication of the cause does double the quantity of collocation. Two men could raise the gun to the required angle twice produce longer and sounder sleep. But a double purging, or a double amount of narcotism, may have remote effects different in kind from the effect of the smaller amount, reducing the case to that of heteropathic laws, discussed in the text. other as causes and effects, is in some | is before his eyes, but he who sees sort a process of analysis. That every fact which begins to exist has a cause, and that this cause must be found in some fact or concourse of facts which immediately preceded the occurrence, may be taken for certain. The whole of the present facts are the infallible result of all past facts, and more immediately of all the facts which existed at the moment previous. Here, then, is a great sequence, which we know to be uniform. If the whole prior state of the entire universe could again recur, it would again be followed by the present state. The question is, how to resolve this complex uniformity into the simpler uniformities which compose it, and assign to each portion of the vast antecedent the portion of the consequent which is attendant on it. This operation, which we have called analytical, inasmuch as it is the resolution of a complex whole into the component elements, is more than a merely mental analysis. No mere contemplation of the phenomena, and partition of them by the intellect alone, will of itself accomplish the end we have now in view. Nevertheless, such a mental partition is an indispensable first step. The order of nature, as perceived at a first glance, presents at every instant a chaos followed by another chaos. We must decompose each chaos into single facts. We must learn to see in the chaotic antecedent a multitude of distinct antecedents, in the chaotic consequent a multitude of distinct consequents. This, supposing it done, will not of itself tell us on which of the antecedents each consequent is invariably attendant. To determine that point, we must endeavour to effect a separation of the facts from one another, not in our minds only, but in nature. The mental analysis, however, must take place first. And every one knows that in the mode of performing it, one intellect differs immensely from another. It is the essence of the act of observing, for the observer is not he who merely sees the thing which what parts that thing is composed of. To do this well is a rare talent. One person, from inattention, or attending only in the wrong place, overlooks half of what he sees; another sets down much more than he sees, confounding it with what he imagines, or with what he infers; another takes note of the kind of all the circumstances, but being inexpert in estimating their degree, leaves the quantity of each vague and uncertain; another sees indeed the whole, but makes such an awkward division of it into parts, throwing things into one mass which require to be separated, and separating others which might more conveniently be considered as one, that the result is much the same, sometimes even worse, than if no analysis had been attempted at all. It would be possible to point out what qualities of mind, and modes of mental culture fit a person for being a good observer: that, however, is a question not of Logic, but of the Theory of Education, in the most enlarged sense of the term. There is not properly an Art of Observing. There may be rules for observing. But these, like rules for inventing, are properly instructions for the preparation of one's own mind; for putting it into the state in which it will be most fitted to observe, or most likely to invent. They are, therefore, essentially rules of self-education, which is a different thing from Logic. They do not teach how to do the thing, but how to make ourselves capable of doing it. They are an art of strengthening the limbs, not an art of using them. The extent and minuteness of observation which may be requisite, and the degree of decomposition to which it may be necessary to carry the mental analysis, depend on the particular purpose in view. To ascertain the state of the whole universe at any particular moment is impossible, but would also be useless. In making chemical experiments, we do not think it necessary to note the To do so, we must be able to meet with some of the antecedents apart from the rest, and observe what follows from them; or some of the consequents, and observe by what they are preceded. We must, in short, follow the Baconian rule of varying the circumstances. This is, indeed, only the first rule of physical inquiry, and not, as some have thought, the sole rule; but it is the foundation of all the rest. position of the planets; because ex- connected with which. In every inperience has shown, as a very super-stance which comes under our obserficial experience is sufficient to show, vation, there are many antecedents that in such cases that circumstance and many consequents. If those is not material to the result: and antecedents could not be severed accordingly, in the ages when men from one another except in thought, believed in the occult influences of or if those consequents never were the heavenly bodies, it might have found apart, it would be impossible been unphilosophical to omit ascer- for us to distinguish (à posteriori at taining the precise condition of those least) the real laws, or to assign to bodies at the moment of the experi- any cause its effect, or to any effect ment. As to the degree of minute-its cause. ness of the mental subdivision, if we were obliged to break down what we observe into its very simplest elements, that is, literally into single facts, it would be difficult to say where we should find them: we can hardly ever affirm that our divisions of any kind have reached the ultimate unit. But this, too, is fortunately unnecessary. The only object of the mental separation is to suggest the requisite physical separation, so that we may either accomplish it ourselves, or seek for it in nature; and we have done enough when we have carried the subdivision as far as the point at which we are able to see what observations or experiments we require. It is only essential, at whatever point our mental decomposition of facts may for the present have stopped, that we should hold ourselves ready and able to carry it farther as occasion requires, and should not allow the freedom of our discriminating faculty to be imprisoned by the swathes and bands of ordinary classification, as was the case with all early speculative inquirers, not excepting the Greeks, to whom it seldom occurred that what was called by one abstract name might, in reality, be several phenomena, or that there was a possibility of decomposing the facts of the universe into any elements but those which ordinary language already recognised. § 2. The different antecedents and consequents being, then, supposed to be, so far as the case requires, ascertained and discriminated from one another, we are to inquire which is The For the purpose of varying the circumstances, we may have recourse (according to a distinction commonly made) either to observation or to experiment; we may either find an instance in nature suited to our purposes, or, by an artificial arrangement of circumstances, make one. value of the instance depends on what it is in itself, not on the mode in which it is obtained: its employment for the purposes of induction depends on the same principles in the one case and in the other, as the uses of money are the same whether it is inherited or acquired. There is, in short, no difference in kind, no real logical distinction, between the two processes of investigation. There are, however, practical distinctions to which it is of considerable importance to advert. It 3. The first and most obvious distinction between Observation and Experiment is, that the latter is an immense extension of the former. not only enables us to produce a much greater number of variations in the circumstances than nature spontaneously offers, but, also, in thousands of cases, to produce the precise sort of variation which we are in want of for | is within the reach of A's influence, discovering the law of the pheno- we have only to observe what alteramenon, -a service which nature, tion is made in that state by the prebeing constructed on a quite different sence of A. scheme from that of facilitating our studies, is seldom so friendly as to bestow upon us. For example, in order to ascertain what principle in the atmosphere enables it to sustain life, the variation we require is that a living animal should be immersed in each component element of the atmosphere separately. But nature does not supply either oxygen or azote in a separate state. We are indebted to artificial experiment for our knowledge that it is the former, and not the latter, which supports respiration; and for our knowledge of the very existence of the two ingredients. Thus far the advantage of experimentation over simple observation is universally recognised : all are aware that it enables us to obtain innumerable combinations of circumstances which are not to be found in nature, and so add to nature's experiments a multitude of experiments of our own. But there is another superiority (or, as Bacon would have expressed it, another prerogative) of instances artificially obtained over spontaneous instances,-of our own experiments over even the same experiments when made by nature,-which is not of less importance, and which is far from being felt and acknowledged in the same degree. When we can produce a phenomenon artificially, we can take it, as it were, home with us, and observe it in the midst of circumstances with which in all other respects we are accurately acquainted. If we desire to know what are the effects of the cause A, and are able to produce A by means at our disposal, we can generally determine at our own discretion, so far as is compatible with the nature of the phenomenon A, the whole of the circumstances which shall be present along with it: and thus, knowing exactly the simulta neous state of everything else which For example, by the electric machine we can produce, in the midst of known circumstances, the phenomena which nature exhibits on a grander scale in the form of lightning and thunder. Now let any one consider what amount of knowledge of the effects and laws of electric agency mankind could have obtained from the mere observation of thunderstorms, and compare it with that which they have gained, and may expect to gain, from electrical and galvanic experiments. This example is the more striking, now that we have reason to believe that electric action is of all natural phenomena (except heat) the most pervading and universal, which, therefore, it might antecedently have been supposed could stand least in need of artificial means of production to enable it to be studied; while the fact is so much the contrary, that without the electric machine, the Leyden jar, and the voltaic battery, we probably should never have suspected the existence of electricity as one of the great agents in nature: the few electric phenomena we should have known of would have continued to be regarded either as supernatural, or as a sort of anomalies and eccentricities in the order of the universe. When we have succeeded in insulating the phenomenon which is the subject of inquiry by placing it among known circumstances, we may produce further variations of circumstances to any extent, and of such kinds as we think best calculated to bring the laws of the phenomenon into a clear light. By introducing one well-defined circumstance after another into the experiment, we obtain assurance of the manner in which the phenomenon behaves under ar indefinite variety of possible circumstances. Thus, chemists, after having obtained some newly-discovered substance in a pure state, (that is, having |