Scope And Bearing Of Physics
( Originally Published 1913 )
Physic's, literally the science of Nature, are restricted to what, in ordinary language, is loosely termed Natural Philosophy. As the second of the Fundamental Sciences we have now to examine their position and bearing in Positive Philosophy. Astronomy and Sociology stand as the Alpha and Omega of Science: the one setting forth the laws of heavenly bodies, the other setting forth the laws which regulate the great movements of Humanity. Between these stand Physics, setting forth as much as may be known of the mystery of this earth, and Physiology (or, more accurately, Biology) as much as may be known of Organic Life. In an inner centre, closely, nay inseparably, connected with both, stands Chemistry, or the science of molecular action. Thus is the circle complete.
One need scarcely say that all such divisions are arbitrary. Nature admits of no distinct lines of demarcation. You cannot say, Here ends the inorganic world, and here begins the organic; you cannot say, Here we see the vegetable domain cease, and here the animal commence; but you can and do say, This rose is a plant, This lion is an animal. Therefore, although Chemistry is inseparable from Physics, and Biology is inseparable from Chemistry, when analysis conducts us to ultimate principles, yet demarcations, such as those just hinted, are necessary and convenient.
Physics did not (according to Comte) begin definitely to disengage itself from Metaphysics, and take a truly positive character, until after the great discoveries of Galileo on the fall of heavy bodies ; whereas Astronomy was really positive, under the geometrical point of view, from the period of the foundation of the School of Alexandria. Here, therefore, we ought not only to look for the direct influence of greater complication in the phenomena, but also expect to find the scientific condition of Physics much less satisfactory than that of Astronomy, as well under the speculative point of view, in respect of the purity and the coordination of their theory, as under the practical point of view, in regard to the extent and exactness of the predictions which result from them. In truth, the gradual formation of this science during the two last centuries was owing to the philosophical impulse of the precepts of Bacon, and the conceptions of Descartes, which necessarily made its general progress much more rational, by directly establishing the fundamental conditions of the universal Positive Method. But, however important this great power may have been in accelerating the natural progress of physical philosophy, the long dominion of primitive metaphysical habits was so absolute, and the positive spirit,—which only use could develope, remained so imperfectly characterised, that this science could not in so short a time acquire complete positivism a state not attained by astronomy itself, as respects the mechanical part of it, before the middle of this period.
Thus, starting from the point where our philosophical examination has now arrived, we find, in the different fundamental sciences remaining for our consideration, more and more profound traces of the metaphysical spirit from which astronomy, alone of all the branches of natural philosophy, is completely freed. This ' anti-scientific influence will not be found limited to details of slight importance. We shall find that it notably alters the fundamental conceptions of science, which has not, even in the case of physics, yet taken entirely its definite philosophical character.
And first, as to the extent of the domain of the science of Physics.
Like Chemistry, Physics have for their object the discovery of the general laws of the Inorganic world. The study of these laws is completely distinct from that of the Science of Life, as from that of Astronomy, which is confined to the consideration of the forms and movements of the great bodies of nature. But the distinction (a real and indispensable one) between Physics and Chemistry is less precisely marked, and modern discoveries are rendering it still more difficult. There are, however, three general considerations which, taken together, make the division between the two sciences quite distinct.
The first consists in the characteristic connection between the necessary generality of truly physical questions, and the speciality no less inherent in investigations purely chemical. Even the philosophers of the seventeenth century had some glimpse of this. All the conceptions of physics, properly so called, are more or less applicable to all bodies whatever ; while, on the contrary, every chemical idea necessarily relates to an action peculiar to certain substances, whatever resemblances we may otherwise find between the different eases. This fundamental contrast between the two categories of phenomena is always distinctly marked. Weight, for example, is shown in all bodies; so also are the phesiomena of thermology, acoustics, optics, and even of electricity ; there being only an inequality of degree in their manifestation. The compositions and decompositions of chemistry, on the other hand, show radically specific properties, varying both in elementary and compound substances. The apparent exception to the generality of physical studies, in the case of magnetism, was dispelled by the discovery of its phenomena being only modifications of the undeniably general phenomena of electricity.
The second elementary consideration distinguishing Physics from Chemistry is of less importance, and indeed it rests on less firm grounds than the preceding one, although susceptible of being turned to proper use. It consists in this, that the phenomena considered in physics refer to the masses, and in chemistry to the molecules ; whence the habitual denomination of molecular physics, formerly given to the latter science.
But purely physical phenomena are often molecular. The weight of a mass, for example, is the total weight of all the separate molecules in it. Again, in chemistry, a certain mass is required to exhibit chemical action. Still there is much truth in the distinction. In order to produce chemical phenomena, one, at least, of the bodies between which the chemical action is to take place, must be in a state of extreme division, and even, most frequently, in a state of true fluidity; and without this, the action will not be produced : while, on the contrary, this preliminary condition is never indispensable to the production of any physical phenomena, properly so called, but is even a circumstance always unfavourable to it, although it is not sufficient constantly to prevent it.
Finally, we may thus distinguish physical phenomena from chemical. In the former, the constitution of the bodies that is to say, the mode of arrangement of their particles may change ; their nature that is to say, the composition of their molecules remains constantly unalterable. In the latter, on the contrary, not only is there always a change of state as respects some one of the bodies in question, but the mutual action of these bodies necessarily alters their nature: and it is a modification of this sort which essentially constitutes the phenomenon. The greater number of the agents considered in physics are doubtless susceptible, when their influence is very energetic or very prolonged, of effecting, by themselves, some compositions and decompositions perfectly identical with chemical action, properly so called ; and this is the reason why there is so natural and so direct a connexion between Physics and Chemistry. But here the phenomena pass from the domain of the first science, and enter that of the second.
The preceding considerations suffice to furnish a precise definition of the proper object of Physics, when strictly circumscribed within their natural limits. In Physics we study the laws which govern the general properties of bodies ordinarily viewed in their mass, and constantly placed in circumstances capable of maintaining intact the composition of their molecules, and most frequently even their state of aggregation. To act up to the true spirit of philosophy, we always require that every science worthy of the name have for its aim, the establishing, on sure grounds, of a corresponding order of predictions. In order, therefore, to complete the definition, it is indispensable to add, that the ultimate object of the theories of physics is to foresee, as exactly as possible, all the phenomena which may be presented by a body placed in any given circumstances, excluding always those which could alter its nature. It is not to be doubted that this end is rarely attained in a complete and perfectly precise manner; but this is only because the science is imperfect. Were its actual imperfection much greater than it is, such would still be its necessary destination.
From this simple and summary exposition of the general object of physical investigations, it is easy to perceive that they necessarily present greater complexity than astronomical studies. The latter are limited to the two most simple and elementary aspects of the bodies there considered,—namely, their forms and their movements. In Physics, on the contrary, the bodies are accessible to all our senses, the general conditions which characterise their actual existence are considered, and they are studied under a great number of different and mutually complicated relations. Physics must inevitably be less perfect than Astronomy; and were it not for the extension of the means of exploration in the former, in accordance with the law mentioned in a previous section, the increased imperfection of Physics might be conceived, à priori, as rendering a science impossible. The method of Comparison is not more applicable in Physics than in Astronomy; but it is otherwise with Experiment. Observation (no longer confined to that of a single sense) and Experiment have their most complete development in Physics. In Organic Physics, it is impossible to obtain the requisite conditions of a perfect experiment. The freedom of choice of the ex-ample (whether natural or artificial) best fitted to manifest the phenomena, constitutes the chief characteristic of the art of philosophical Experiment ; and this freedom is found more in Physics than in Chemistry. It is to the development of Physics that the creation of the art of Experiment is due.
Next to the rational use of the Experimental Method, the application, more or less complete, of Mathematical Analysis forms the principal basis on which the perfection of Physics rests. It is here that the actual range of this Analysis in natural philosophy finds its limit ; and in the sequel of Comte's work it is shown how chimerical it would be to expect that its domain will be further extended, even to Chemistry, with any real efficacy. The comparative fixity and simplicity of physical phenomena ought naturally to permit an extensive employment of Mathematics, although they are much less adapted to physical than to astronomical studies. This application may occur under two very different forms, the one direct, the other indirect. The first takes place when the phenomena are such as to permit of our immediately finding in them a fundamental numerical law, which becomes the basis of a more or less prolonged series of analytical deductions ; as in the eminent example of Fourier when he created his beautiful mathematical theory of the distribution of caloric, founded altogether on the principle of the thermological action between two bodies being proportional to the difference of their temperatures. Most frequently, on the contrary, mathematical analysis is introduced only indirectly; that is, after the phenomena have been connected with some geometrical or mechanical law by means of a course of experiment ; and then, it is not to Physics, properly speaking, that the analysis is applied, but to geometry, or mechanics. Among other examples, we may cite the theories of reflection and of refraction, as respects geometry; and those of weight or of harmonics, as respects mechanics.
The application of mathematics to physics ought only to take place, and that with extreme circumspection, when assurance has been obtained of the reality of the physical facts from which the mathematical deductions are to be made. The neglect of this rule has occasioned numerous analytical labours founded on wild hypotheses or on chimerical conceptions, and has often converted physical studies into mere mathematical exercises. To avoid these evils, natural philosophers ought themselves to be familiar with as much of mathematics as would enable them to make the proper application of Mathematics to physics, instead of leaving it to mathematicians, destitute of true ideas on the nature of physical inquiry.
Comte—whose language has here been almost verbally employed adds, that the services rendered by Mathematics to Physics have been immense. They have given to Physics that admirable precision and perfect coordination which always characterise their employment. But still, he remarks, they are less applicable to Physics than to Astronomy. In Physics, we have, more or less,to overlook the essential conditions of the problem, and in so far to alter the actual nature of the phenomena, in order to permit the use of analysis; while, to ensure correctness and reality in physical studies, it is necessary to have recourse both to Experiment and Analysis,checking and aiding the latter by the former, without subordinating the one to the other.