says the Doctor, "the important end of knowing their causes, besides gratifying our curiosity, is, that we may know when to expect them, or how to bring them about. This is very often of real importance in life: and this purpose is served, by knowing what, by the course of nature, goes before them and is connected with them; and this we call the CAUSE of such a phenomenon.

"If a magnet be brought near to a mariner's compass, the needle, which was before at rest, immediately begins to move, and bends its course towards the magnet, or perhaps the contrary way. If an unlearned sailor is asked the cause of this motion of the needle, he is at no loss for an answer. He tells you it is the magnet, and the proof is clear; for remove the magnet and the effect ceases: bring it near, and the effect is again produced. It is, therefore, evident to sense, that the magnet is the cause of this effect.

"A Cartesian philosopher enters deeper into the cause of this phenomenon. He observes, that the magnet does not touch the needle, and, therefore, can give it no impulse. He pities the ignorance of the sailor. The effect is produced, says he, by magnetic effluvia, or subtile matter, which passes from the magnet to the needle, and forces it from its place. He can even show you in a figure, where these magnetic effluvia issue from the magnet, what round they take, and what way they

return home again. And thus he thinks he comprehends perfectly how, and by what cause, the motion of the needle is produced.

"A Newtonian philosopher, inquires what proof can be offered for the existence of magnetic effluvia, and can find none. He, therefore, holds it as a fiction, a hypothesis; and he has learned that hypotheses ought to have no place in the philosophy of nature. He confesses his ignorance of the real cause of this motion, and thinks, that his business, as a philosopher, is only to find from experiment the laws by which it is regulated in all

cases.

"These three persons differ much in their sentiments with regard to the real cause of this phenomenon; and the man who knows most, is he who is sensible that he knows nothing of the matter. Yet, all the three speak the same language, and acknowledge that the cause of this motion is the attractive or repulsive power of the magnet.

"The grandest discovery ever made in natural philosophy, was that of the law of gravitation, which opens such a view of our planetary system, that it looks like something divine. But the author of this discovery was perfectly aware, that he discovered no real cause, but only the law or rule, according to which the unknown cause operates.

"Natural philosophers, who think accurately, have a precise meaning to the terms they use in

the science; and when they pretend to show the cause of any phenomenon of nature, they mean by the cause, a law of nature, of which that phenomenon is a necessary consequence.

"The whole object of natural philosophy, as Newton expressly teaches, is reducible to these two heads; first, by just induction from experiment and observation, to discover the laws of nature, and then to apply those laws to the solution of the phenomena of nature. This was all that this great philosopher attempted, and all that he thought attainable. And this, indeed, he attained in a great measure, with regard to the motions of our planetary system, and with regard to the rays of light.

"But supposing that all the phenomena that fall within the reach of our senses, were accounted for from general laws of nature, justly deduced from experience; that is, supposing natural philosophy brought to its utmost perfection, it does not discover the efficient cause of any one phenomenon in nature.

"The laws of nature are the rules according to which the effects are produced; but there must be a cause which operates according to these rules. The rules of navigation never navigated a ship. The rules of architecture never built a house."

Enough has been quoted from Dr. Reid, for the purposes of the present chapter. And, without making any remarks on it, we proceed to consider

what Dr. Brown has written on the same subject.

This eloquent and ingenious writer has taken upon himself the defence of Mr. Hume's notion in all its leading features, and denies that we have any notion of power, except the uniform conjunction of events in any sequence. A cause, according to him, never in any case means any thing more than a uniform and invariable antecedent; and power is the mere fact of immediate and invariable antecedent.

"Without experience," he observes,* "we could not predict that on the application of a spark, gunpowder would detonate, and that snow would not. There is nothing in the appearance of the one or the other that could lead to any such conclusion. Without experience we could not know that a ball in motion, when it meets another at rest, should force that other to quit its place. But experience teaches us the past only, not the future; why is it then that we believe that continual similarity of the future to the past, which constitutes, or at least is implied in our notion of power? A stone tends to the earth-A stone will always tend to the earth, are not the same proposition; nor can the first be said to involve the second. It is not to

* Brown on the Mind, Lecture VI. I have taken the liberty of somewhat abridging, wherever Dr. Brown was too diffuse to quote at full length.

experience, then, alone, that we must have recourse for the origin of the belief, but to some other principle, which converts the simple facts of experience into a general expectation, or confidence, that is afterwards to be physically the guide of all our plans and actions.

"This principle, since it cannot be derived from experience itself, which relates only to the past, must be an original principle of our nature. There is a tendency in the very constitution of the mind from which the expectation arises, a tendency that, in every thing which it adds to the mere facts of experience, may be truly termed instinctive. It is wonderful indeed-for what is not wonderful? --that any belief should arise as to a future, which as yet has no existence. But, when we consider who it was who formed us, it would in truth be more wonderful if the mind had been so differently constituted, that the belief had not arisen; because, in that case, the phenomena of nature, however regularly arranged, would have been arranged in vain.

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Mr. Hume, indeed, has attempted to show, that the belief of the similarity of future sequences of events, is reducible to the influence of custom, without the necessity of any intuitive expectation; but he has completely failed in the reasoning with which he has endeavoured to support this opinion. Custom may account for the mere suggestion of one object by another, as a part of a train of images,