causes which we trace in operation in the material world. The evidence on which our knowledge of these causes depends is that afforded by induction, which we have already been engaged in tracing; and in proceeding, as we are now about to do, to the more direct consideration of their nature, we shall find that this discussion has not been misplaced; and that, in fact, in studying the evidence, we have arrived at some of the most important observations for bringing us to the apprehension of the nature of physical causes. In tracing the essential grounds of induction, it will be found that we have elicited what will be our safest guide in the inquiry into the principle of causation.

From the earliest periods at which intellectual pursuits have attained anything like a due place in the estimation of mankind, a high rank has always been assigned to the study of the causes of things. Surrounded as we are by the most stupendous scene of natural wonders, it would indeed be surprising if the curiosity of man were not excited, even in an early stage of civilization, to learn something of the nature and source of those effects which he daily witnesses in the magnificent phenomena of the material world. And we accordingly find that from the earliest times at which the human race has been sufficiently advanced to give attention to such subjects, the inquiry into the nature and relations, the dependence and connexion, of natural phenomena, has obtained at least some share of attention; and

though pursued only by a few, has conferred upon them, at all times, a certain degree of reputation even among the uninstructed, while with those of more enlightened ideas, a knowledge of the causes of those effects which we daily witness has been regarded as among the highest objects of intellectual attainment; and to be permitted thus to penetrate, as it were, into the hidden processes by which nature works, has been esteemed the most elevated privilege of philosophy. It is a species of knowledge of extreme interest and value in itself, and embraces in its applications, some of the most important and even momentous questions which can occupy human contemplation.

Meaning of the term "Cause."

In order to pursue our inquiry into the nature of Physical Causes, it will be essential, in the first instance, to distinguish, as clearly as we can, the meaning annexed to the term.

In common language, the term "cause" is used with considerable latitude of meaning; and even in many discussions pretending to a philosophic character, a slight examination will show that it bears several distinct kinds of signification. We are apt to use the same word, and thence imagine that we are speaking of the same thing, in cases which are essentially different; though there is doubtless enough of apparent resemblance to mislead inaccu

rate thinkers into the notion of identity. Hence the ambiguity and fallacy which prevail in some of the most important inquiries connected with this subject; and the manifest necessity for attention to accurate distinction of the meaning of terms.

In ordinary affairs, we talk of the "cause" of an undertaking, or the "cause" of our conduct. Again we speak of the "cause" of an historical event; and we apply the term to matters of reasoning or belief in the conjunction "because." We mean the motive of our actions; the ground or evidence of our opinion; the train of circumstances which brought about an event in history. In these and the like cases, we may trace a general analogy, which has led to the application of the same term. In all of them we refer to some sort of moral influence exercised either by concurrent circumstances upon human motives or convictions, or by human agency (individual or collective) upon events.

In the discussion of causes and effects, as we contemplate them in the natural world, and in connexion with physical science, it is more especially necessary to guard against the vague use of terms. And in proceeding to the more precise examination of the nature of physical causes, we may consider more particularly, as a preliminary illustration in the way of contrast, two familiar instances of the use of the term "cause."

We may say the cause of the motions of a watch is the tendency of the main-spring to unwind itself;

and the cause of the flight of the cricket-ball is the voluntary effort of the player. These are two instances which would seem, at first sight, closely to resemble each other; but when accurately examined, we find an important distinction between them. In the former instance, we trace the order of dependence of the motions from the index to the wheels, from the wheels to the fusee, and so up to the tendency of the spring to unwind; and this we refer to the property of elasticity; which again may possibly depend on some still higher principle in the nature and arrangement of the particles of which elastic bodies are composed. But to whatever extent we may advance in thus analyzing the effect up to its simplest elements, one thing is all along manifest; viz., that the very highest principle of any such series must essentially be some general, fixed, inherent, property of matter; by virtue of which it is capable of being influenced in particular ways, and by particular agents; but yet is wholly inert, and incapable of arbitrarily originating any of the effects referred to.

In the second case, we may observe, it is true, a like series of effects in succession dependent one on another. Motion is communicated mechanically to the ball from the sudden action of the arm; this results from the contraction of the muscles acting on the bones as levers; the muscular contraction again may be shown to depend on some peculiar influence of the nerves; this again may possibly

be traced to some higher principle; we may advance, in short, as far as physiological science can carry us; and thus far, this and the former case are exactly alike. But here at the commencement of the whole train, there must still be an influence or cause of some kind different from any mechanical power; depending on voluntary agency; capable of originating the series of consequences from itself; acting by different laws from those of matter; in a word, an agency or influence of a moral kind: Or (in the graphic language of Sir J. Herschel*), we must include "a distinct and immediate personal consciousness of causation in the enumeration of that sequence of events by which the volition of the mind is made to terminate in the motion of material objects; I mean the consciousness of effort, as a thing entirely distinct from mere desire or volition on the one hand, and from mere spasmodic contraction of the muscles on the other."

Such a voluntary agency, such an influence or power, of which we feel conscious, and which implies the action (however incomprehensible,) of mind on matter, is what we may properly distinguish by the term "moral causation." The former case we may call, by way of contradistinction, an instance of "physical causation." In the study of causes acting in the natural world, we must care

* Astronomy, p. 232.

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