adhesion, we can also perceive that the particles, when once brought into a common polarization, would be likely to maintain their constrained axial position permanently, provided that the adhesive resistances of the molecules should exceed their magnetic resistances. Such a behav ior we find presented by hardened steel, to which habit the name "specific coercitive power" has been given. There is obviously no transfer of virtue from the magnetizing to the magnetized body. On the contrary, the former is actually strengthened by its evolution of the manifestation in the latter-a result in perfect accord with the supposition of a reaction of mutual preexisting attrac tions. It is familiar that by holding a bar of steel in the direction of the earth's magnetic pole, or rather of its magnetic dip, and giving the end of the bar a few taps with a hammer, we can at once induce the magnetic condition. Here obviously the molecular vibrations from the blow have facilitated the rotations necessary to bring the particles into axial accord. The work expended therefore in developing the magnetism of a steel bar, whether by the mechanical passes of an artificial magnet, the longcontinued induction of the terrestrial polarity, or the molecular disturbance of an eletrical coil, is simply that required to overcome the original resistances to the changed condition. The magnetic force, or dual forces, must be regarded as primitive, constant, unchangeable attributes of the ultimate particles of matter; as incapable of increase, of diminution, or of transfer, as gravitation itself. And the notable discovery of diamagnetism, by Faraday, leads us to believe that all matter has this polar quality indelibly stamped upon it in varying degrees; the molecules of nitrogen possessing it in the smallest degree of any known element. Analogical reasoning would appear to justify the conclusion that electrical attraction and repulsion (capricious, ephemeral, and mysterious as they appear) belong to the same category of original and unalterable molecular properties, although it is by no means easy to give so rational an account of the phenomena observed as in the case of magnetism. The fact that both are polar forces, exhibiting a duplex action; that in both cases similar states or poles repel each other, and opposite states or poles attract each other; that these conditions of attraction and repulsion apply equally or indifferently to either pole; and that an. opposing polarity may be induced by approach in other matter, would certainly indicate a very similar nature and seat of influence. In the apparent transfer, however, of electricity by contact or discharge, and in the neutral equilibrium immediately resulting, there is an action sui generis; as also in its manifestation as a differential of chemical, or of thermal activities. In the mutual reactions of the magnet and the electrical current, still more puzzling phenomena are presented; and without attempting to discuss Ampere's ingenious theory of the "solenoid," the observed fact that each does exhibit a torsional or tangential action upon the other is one which has no parallel or analogue in any other of the known natural forces. In the quasi-magnetic behavior of electrical currents, whatever the vehicle or electrode, occurs a further extension of the same peculiarity. Notwithstanding all these difficulties, and the intimate relations of "dynamic" with so-called "static electricity," a more comprehensive and rational theory of this most abstruse subject may hereafter establish as radical a distinction between the molecular movements constituting electrical currents, and the molecular capacities of polarity, or of electrical attraction and repulsion, as has been found to exist between light or heat and chemical affinities or molecular repulsions. Nor is the inference here suggested affected by the fact that Joule, in 1843, derived his first approximation to the mechanical equivalent of heat from experiments "on the calorific effects of magneto-electricity,' any more than it is by the fact that we accept terrestrial gravity, at the earth's surface, as the standard of comparison for all forms of energy. It was seen at the outset that the conditions of antagonistic molecular attraction and repulsion, such as we find in the actual constitution of matter, were essential postulates to the theory of the conservation or persistence of force. We have been led to the conclusion that these same antagonistic principles constitute equally the real, efficient origin of force. And though we are provided with no general term to embrace these primordial, indestructible, immutable, statical centers of force, and to distinguish them from those other derivative, evanescent, and convertible forms of energy, exhibited either in the potential of constrained position, or in the actual of changing position, yet the two classes appear to be so essentially dissimilar that it may well be doubted whether the language very frequently employed by writers to express the correlations and transformations of material forces is really an accurate statement of the fact. If it be true that all phenomena of energy may be traced back ultimately to molecular attractions and repulsions as their primeval parents, and if these same attractions and repulsions are found to be persistent, ever-present, and unexchangeable, however frequently matter in its protean character may be shifted (so to speak) from the active dominion of the one to that of another, it would seem to be exceedingly improbable that, conversely, any form of molecular attraction or repulsion can be produced or derived from motion, or from the ordinary manifestations of dynamic energy. If this be so, we are not warranted in speaking of the correlations of gravity, of cohesion, of chemical affinity, and of magnetism, in the same sense in which we apply the term correlation to the secondary or convertible forms of force, as among themselves, and as connected with their primaries. Mr. Joule's paper, read before the British Association, August, 1843, was published in the L. E. D. Phil. Mag. of that year, Vol. XXIII, pages 263, 347, and 435. INDUCTION AND DEDUCTION. A DISCOURSE BY JUSTUS BARON VON LIEBIG. (Translated for the Smithsonian Institution.) The ideas of the generality of men respecting the nature of scientific research are so imperfect and erroneous that it will not, perhaps, be without interest to many if I attempt to elucidate and complete the views which I advanced on this subject in a former discourse on Francis Bacon, of Verulam. Philosophers pursue in general two methods of inquiry in regard to the phenomena or laws of nature, induction and deduction; they are in effect but different processes, while their object is the same; the distinction between them depends upon the point of outset; the deductive method sets out from generals, the inductive from particulars; in the combination of the two induction precedes deduction. The nature of induction, according to Aristotle's view of it, may perhaps be best illustrated by the example which he himself gives of an inductive conclusion: Man, the horse, the mule, &c., live long. Man, the horse, the mule, &c., have little gall. Therefore, all animals that have little gall live long. This mode of conclusion, if so we must call it, is a very easy one to the inquirer; but what is here styled a conclusion is only the observation of the juxtaposition of two phenomena; scarcity of gall is a fact which accompanies long life; it is part of a whole, and the conclusion no syllogism, including in itself the reason of the dependence of longev ity on the paucity of the secretion in question. We need only substi tute in the middle term, instead of gall, any other simultaneous fact peculiar to certain animals, for instance: in order at once to perceive that the connection of these with longevity is purely arbitrary and rests on no operation of the understanding The philosopher, for the explanation of a phenomenon of nature or of a process, seeks to assign a connection between the parts thereof which have come under his observation, and first of all sets out with the supposition, as regards two facts which constantly accompany the phenome non or process, that they postulate one another, or that one is dependent on the other; but this is merely an idea having no real basis for its support, but simply a perception which may or may not arise in the mind of any one. Aristotle denoted induction as being the passage from particulars to generals, since, in physical inquiry, our first concern is with the knowledge of the phenomenon and afterward with its explanation; but in this sense it is clear that he regarded induction not as a method, but as a rule of investigation. It is plain that if all the forces of nature and their laws were known to us, if we knew all things in their nature, action, and properties, the investigation of a particular process and its explanation would be a simple deductive problem; each single case would then be soluble through a conclusion of the understanding. Suppose, for instance, that the rusting of iron in the air were the point to be explained; the previous examination of rust has determined that it contains iron, oxygen, and water; the composition of air is also known; the elements, therefore, for explaining the process of rusting are before us, but further inquiry shows us that iron in oxygen in the presence of the vapor of water does not rust; there must, then, be some constituent principle of the air, besides oxygen and vapor, in order that iron should undergo the process of rusting; now we know that the air actually contains a very small portion of carbonic acid, and examination shows that a mere trace of carbonic acid suffices, with sufficient access of oxygen, to convert a large mass of iron into oxide; but the rust itself contains no carbonic acid. The question then is: What part does this acid play in the process? Another known fact now suffices to complete the explanation; this is the action of the oxidulated carbonate of iron; in damp air it attracts oxygen and is converted into the higher oxide which enters not into combination with carbonic acid; it is by the rusting of the metal that the lower oxide first originates, and this combines with carbonic acid, which through the passage of the oxidulate into free oxide becomes capable of exerting in a hundred fold degree its original action on the metal, so that gradually the whole piece is throughout converted into iron-rust. Inquiry further establishes that there is a special case where iron in damp air, even without the presence of carbonic acid, is thus rusted, when the air, namely, contains ammonia; but that in that case the rust does not extend, and that, lastly, an electrical process is coöperative with the rusting. To this class of investigations belongs also that of the production of dew by Dr. Wells. That dew is a watery precipitate produced by refrigeration admitted of no doubt, nor that the modes of refrigeration were only two. The problem only turned upon the question, whether the conditions of the cooling were dependent on conduction or on radiation, which point was susceptible of determination by experiments guided by known laws. To inquiries of this sort no exterior difficulties oppose themselves, and, for conducting them, knowledge and the correct appreciation of relations abundantly suffice; they rarely occur, because the physical inquirer, for most of his problems, does not find ready prepared the thought-material requisite for his mental process; it should also be remarked that by these our insight into the nature of phenomena is indeed rendered clearer and more thorough, but that the boundaries of science are not thereby enlarged. In the great number of other inquiries, the inquirer is confronted by obstacles which, with the whole stock of knowledge furnished by science and with the most perfect powers of discrimination, he cannot remove, and these are new facts or phenomena which pertain to unknown laws, which are not accessible to the understanding from a deficiency of the intervening facts necessary to his ideas. For this class of inquiries there must coöperate, in the case of the philosophical inquirer, something which essentially characterizes his mind, and that is the force of imagination. The sum of what we know respecting nature and its forces is, in fact, so small when compared with what we do not know respecting them, that the physicists of our times find themselves, in a majority of cases, precisely in the condition of those of the sixteenth century as regards those things which to them were unintelligible but to us are easy; there is for us, as there was for them, a defect of clearly comprehensible facts essential to the deductive process; in the failure of a single one of these the intellect stands before a chasm which it cannot fill up; in that earlier time the force of imagination was called in aid to an extent which we regard now as wholly inadmissible. The advantage we have over the early inquirers rests therefore not on increased intellectual powers or on the superior delicacy and penetration of our senses, but on a greater affluence of facts or experiences, that is, on an accumulation of materials for the operations of the understanding. Hence there is no doubt to be raised respecting our relative position; and yet there are but few who have a clear idea of the sources from which the constantly increasing store of these materials for thought is derived. If we cast a glance backward on the history of the so-called inductive sciences, we at once recognize that for centuries they had the character of an art. Until Newton, astronomy and mechanics were arts; the same were physics until the time of Galileo; and chemistry up to that of Bergmann. Boerhaave defines chemistry as the ars docens exercere certas. physicas operationes. Art and science are essentially distinguished from one another by their different aims.* That of art is the search for or the finding of facts; that of science is the explanation of them. By art, of course, we do not here mean any of the fine arts. The artificer seeks to attain an object; the experimental artificer seeks a thing. From particu *The aim of art is the discovery of facts; that of science the discovery of principles and laws.-J. H. |