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i. In the first place then a man may regard himself alone, and isolate the laws of limitation under which his impressions are received from the objects which stimulate his senses. The ideas

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of time and space, of succession and extension, when once apprehended in their most simple and absolute form become the sufficient foundation for wide and complicated conclusions. When the ideas have once been called into play, there is no longer any need that the inquirer should turn a single thought to phenomena. An experiment may illustrate one of his results, but it is impossible to conceive any experiment which could either confirm his legitimate deductions or shake them. The utmost developments of the relations of number and figure are absolute for man. facts with which he deals in them are not only assumed to be constant: for him they are constant. Nothing, as long as he is what he is, can interfere with the certainty of his deductions. But we must observe that we are not justified in extending the limitations of our perceptions to any other order of beings. Obviously we cannot extend them to an Infinite Being. They may be shadows or fragments of something larger, grander, immeasurably more comprehensive, into which they are capable of being taken up and resolved. But however this may be, we cannot give definiteness

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Physical truth.

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to such thoughts; and we come back to the marks of our primary group of sciences. The sphere is man himself. The subject is the characteristic limitations of his perceptions. The method is deductive. The verification of the results lies in the possibility of their resolution into elements of which the opposite is unthinkable.

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ii. But man cannot rest here. strained to look continuously without. He regards self, and he regards the world. And however much he may be tempted to mould the phenomena of the world into some preconceived shape, he is soon compelled to abandon the attempt. Prior to observation he is utterly unable to predict the laws which represent the action of the various forces about him. To the last he has no complete assurance that he has detected all the forces which are at work and ready to reveal themselves. But by the accumulation of experience he can do much in grouping vast series of phenomena under adequate formulas; and just as he isolates the abstract conditions of observation (conditions of time and space) from the concrete facts through which they are made known to men, he can isolate also in imagination the operation of each force; and when he has done so, but not till then, the method of deduction can be applied to data which

are treated separately as absolute. The assumed conditions are, of course, in this case imaginary; but where the actual phenomena are resolvable into the resultants of few elements the recurrence of the phenomena can be predicted with an assurance proportioned to their simplicity. But the certainty obtainable in this region is separated by an impassable chasm from the certainty which belongs to the former group of facts.

It reposes on a twofold assumption, which from the nature of the case can never cease to be an assumption. It is assumed that the observed law is constant, and it is assumed that no force hitherto unperceived will hereafter interfere with the observed manifestation of the law. Now even as things are, late physical researches as we have already seen suggest grounds for believing that the present state of the world could not have come about from the uniform action of the forces which

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we can now observe; and the fact that energy being constantly dissipated, that is, I imagine, stored up though not used, seems to indicate that provision is being made for some hitherto unknown revelation of being. Perhaps indeed, if I may venture on a conjecture, the phenomena of physics may be conceived of best as falling under some vast progressive periodic cycles, an ascending

III.]

in Physical law.

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spiral as it were, though for the infinitesimal fragments of their course during which we can observe them, no appreciable error is made by assuming the constancy of the laws which express their general form.

However I have no right to enter further on this field, and all that I desire to indicate is that we have within it a new kind of phenomena, subject to new conditions only partially discoverable in their relations to ourselves, a new method of inquiry, a new test of verification. The sphere is external nature: the method is inductive: the verification is experiment and prediction: while at the same time the former sphere, the former method, the former test underlie these, and is unmodifiable by them. Physical Truth, in a word, is not homogeneous with mathematical Truth, but all physical results involve a mathematical foundation. They rest, that is, in their expression upon the limitations of succession.

But we must go further. Hitherto we have considered only the manifestation of inorganic being. All investigation tends to confirm the instinct which separates physical force from life. Omne vivum ex vivo is a principle which brings us face to face with a new series of

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phenomena. And even if future researches should shew that there is, or make it probable that there has been, an evolution of life from matter, the region of life will still remain clearly distinct. We have here to deal with the fullest development of phenomena and not with their inchoate stage. In the case of living bodies then all the observed laws of inorganic being hold good so far as these bodies can be considered simply as inorganic, but no further. All the laws which limit our observation hold good in the deductions which can be drawn from them. But life itself is an element wholly different in order from those with which we have dealt hitherto. The variety, the complexity, the cumulative transmission of its manifestations, render experiment and prediction for the most part nugatory. This is true both of the single life and of the sum of being. We cannot here, except in the broadest generalizations, assume permanence in the conditions of the problem: we cannot assume permanence in the mysterious energy of life itself: we cannot affect to leave out of consideration the interference of individual influences, which, from whatever source they spring, are at least incalculable. We find ourselves in the presence of a movement due to an immeasurable combination of concurrent or conflicting powers. It is a grand truth that 'the

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