LIMITS OF INVESTIGATION. 15 mensurable with scientific truths. We will therefore abide by the words of Goethe: Whoso has art and science found, Religion, too, has he; Who has nor art nor science found, And now, having provisionally averted uncalled-for objections and conflicts with ambiguous ideas, we may quietly consider the limits of natural science. Let us first pause at the address delivered with general approval by the physiologist Dubois-Reymond, at the fiftieth assembly of German Naturalists and Physicians. He made reference to a passage in the classical works of Laplace, in the Introduction to the Theory of Science, which we cannot refrain from quoting in full. The author of the "Mechanism of the Heavens," says: "Present events are connected with the events of the past by a link resting on the obvious principle that a thing cannot begin to exist without a cause which produces it. This maxim, known by the name of the Principle of Sufficient Cause, extends likewise to events with which it is not supposed to come in contact. Even the freest will cannot evoke them without a determining impulse." "We must, therefore, regard the present condition of the universe as the consequence of its former, and the cause of its future, condition. A mind, for a given moment acquainted with all the forces which animate Nature, and the reciprocal relations of the entities of which it is * Wer Wissenschafft und Kunst besitzt, Hat auch Religion; Wer jene beiden nicht besitzt, Der habe Religion. composed-possessed, moreover, of powers of comprehension sufficient to submit all these facts to analysis, would be able to reduce to a single formula the motions of the largest heavenly body and of the lightest atom. To such a mind nothing would be uncertain, and the future, like the past, would lie open before it. The human mind in all the perfection which it has been able to give to astronomy, offers but a faint image of such a mind as this." "All efforts of the human intellect in the search for truth tend to approach the mind above portrayed, but will always remain infinitely removed from it." The Prussian physiologist then quotes the "Thou art like the Spirit whom thou comprehendest" of Faust;* and is of opinion that, in the abstract, the formula of the universe is therefore not impenetrable to the human intellect. But we own we are cordially indifferent to an abstract perfection which never comes to light, and regard the unattainableness of this vague formula of the universe as a very endurable limit to human inquiry. But independently of the dubious consolation of the formula of the universe, we must agree with DuboisReymond, when he considers that the limits, before which the highest conceivable intelligence must pause, are also insurmountable to man. In accordance with the views now prevailing among physicists and biologists, Dubois-Reymond has thus specified the only limit given to the investigation of nature3: “The knowledge of natural science, more closely defined above, is no real knowledge. In the attempt to comprehend the constant, to which the mutations in * Du gleichst dem Geist, den du begreifst. ATOMS IDEALLY REPRESENTED. 17 the material world may be traced back, we stumble on insoluble contradictions. An atom contemplated as a minute, indivisible, inert mass, from which forces emanate, is a chimera. In the impossibility of comprehending the nature of matter and force lies the only limit to the knowledge of natural science." These propositions require some elucidation. Beyond the subdivision mechanically possible, we must think of substance or matter as consisting of particles ultimately indivisible. Of these atoms, according to the present. standpoint of science, we are obliged to admit as many different species as are not chemically reducible to more simple elements. Now there is no doubt that these atoms are, in the actual sense of the word, imaginary, hypothetical quantities; and theory seems to indicate. that all matter, in the most different phenomena in the material world, is based on a single species of atom. Every manual of physics or physiology will show that, in order to understand and calculate the properties of these atoms and their combinations into the ingredients of compound bodies, susceptible of chemical analysis, they are ideally represented under various material forms, spherical, cubical, &c.; furthermore, that in their combinations and co-operations as bodies, they must be contemplated as surrounded by a rarefied atmosphere of an universally diffused ether. But the atom itself, and therefore the nature of matter, is something incomprehensible, unattainable. In these atoms, forces are inherent, which display themselves in attractions and repulsions, and in motion in general. But the final cause of these motions, and how far these motions are, as it were, identical with the existence of the atoms, is likewise included in the incomprehensibility of matter. "If we pass over this," says Dubois-Reymond again, “the universe is approximately comprehensible. Even the appearance on the earth of life in the abstract does not render it incomprehensible. For life in the abstract, contemplated from the standpoint of the theoretical investigation of nature, is merely the arrangement of molecules in a state of more or less stable equilibrium, and the introduction of an exchange of material, partly by their own elastic force, partly by motion transferred from without. It is a misapprehension to see anything supernatural in this." This is the point which is usually contested with the greatest vehemence. If all the motions and states of quiescence of the inanimate world can be thoroughly explained, the inexplicable must commence with the basis of life. The imputation cast upon the reasoning powers by this assumption may be formularized as follows, in the question put by another sound and thoughtful physiologist, A. Fick:* "Are the characteristics of such a particle, as already explained, applicable and effective during the period of its sojourn in an organism? Thus, for instance, will the motions of a particle of oxygen be affected and altered by a neighbouring particle of hydrogen, in accordance with the same laws, when one or both form part of an organism, as when they are out of it?" To reply in the negative is to avow the vitalistic conception of life, that is, to take refuge in unknown forces quite extraneous to matter, and to admit that the self-same particle can vary its nature, according HEAT, A MODE OF MOTION. 19 to whether it be internal or external to an organism, is, in other words, to affirm a miracle. If this is weighed against the physical view, "which in its perfection reduces every organic process to a problem of pure mechanics," it may be done in the certainly impartial words of the naturalist just quoted: "I am of opinion that the mechanical view of organic life is demonstrated only when all the motions in an organism are shown to be the effects of forces, which at other times also are inherent in the atoms. But similarly I should regard the vitalistic view as proved, if in any case a particular motion actually observed to take place in an organism were shown to be mechanically impossible. At present, neither is to be thought of. Nevertheless, if a decision must be made without full proof, I provisionally profess myself unequivocally in favour of the mechanical view. Not only does it recommend itself à priori by its superior probability and simplicity, but the progress of scientific development raises it almost to a certainty. When it is seen how certain phenomena-such as the evolution of animal heat, which it was formerly believed could be explained only by vital force-are now ascribed, even by those who in general assume the existence of a special vital force, to the universally active forces of the material particles, we find ourselves almost forced to the conviction that by degrees all the phenomena of life will become susceptible of mechanical explanation." For the elucidation of the example just given of animal heat, let us observe that modern physics have learnt to know heat as a peculiar mode of motion. The motion. of the hammer as it falls upon the anvil is not lost, but |