The theoretical views which one generation of discoverers establishes, become the facts from which the next generation advances to new theories. As men rise from the particular to the general, so, in the same manner, they rise from what is general to what is more general. Each induction supplies the materials of fresh inductions; each generalization, with all that it embraces in its circle, may be found to be but one of many circles, comprehended within the circuit of some wider generalization.

This remark has already been made, and illustrated, in the History of the Inductive Sciences; and, in truth, the whole of the history of science is full of suggestions and exemplifications of this course of things. It may be convenient, however, to select a few instances which may further explain and confirm this view of the progress of scientific knowledge.

The most conspicuous instance of this succession is to be found in that science which has been progressive from the beginning of the world to our own times, and which exhibits by far the richest collection of successive discoveries: I mean Astronomy. It is easy to see that each of these successive discoveries depended on those antecedently made, and that in each, the truths which were the highest point of the knowledge of one age were the fundamental basis of the efforts of the age which came next. Thus we find, in the days of Greek discovery, Hipparchus and Ptolemy combining and explaining the particular facts of the motion of the sun, moon, and planets, by means of the theory of epicycles and eccentrics;-a highly important step, which gave an intelligible connexion and rule to the motions of each of these luminaries. When these cycles and epicycles, thus truly representing the apparent motions of the heavenly bodies, had accumulated to an inconvenient amount, by the discovery of many inequalities in the observed motions, Copernicus showed that their effects might all be more simply included, by making the sun the center of motion of the planets, instead of

2 Hist. Inductive Sciences, b. vii. c. ii. sect. 5.

the earth. But in this new view, he still retained the epicycles and eccentrics which governed the motion of each body. Tycho Brahe's observations, and Kepler's calculations, showed that, besides the vast number of facts which the epicyclical theory could account for, there were some which it would not exactly include, and Kepler was led to the persuasion that the planets move in ellipses. But this view of motion was at first conceived by Kepler as a modification of the conception of epicycles. On one occasion he blames himself for not sooner seeing that such a modification was possible. 'What an absurdity on my part!' he cries; 'as if libration in the diameter of the epicycle might not come to the same thing as motion in the ellipse.' But again; Kepler's laws of the elliptical motion of the planets were established; and these laws immediately became the facts on which the mathematicians had to found their mechanical theories. From these facts, Newton, as we have related, proved that the central force of the sun retains the planets in their orbits, according to the law of the inverse square of the distance. The same law was shown to prevail in the gravitation of the earth. It was shown, too, by induction from the motions of Jupiter and Saturn, that the planets attract each other; by calculations from the figure of the earth, that the parts of the earth attract each other; and, by considering the course of the tides, that the sun and moon attract the waters of the ocean. And all these curious discoveries being established as facts, the subject was ready for another step of generalization. By an unparalleled rapidity in the progress of discovery in this case, not only were all the inductions which we have first mentioned made by one individual, but the new advance, the higher flight, the closing victory, fell to the lot of the same extraordinary person.

The attraction of the sun upon the planets, of the moon upon the earth, of the planets on each other, of the parts of the earth on themselves, of the sun and

3 Hist. Inductive Sciences, b. v. c. iv. sect. 3.

moon upon the ocean;-all these truths, each of it a great discovery, were included by Newton in higher generalization, of the universal gravitation matter, by which each particle is drawn to every ot according to the law of the inverse square: and t this long advance from discovery to discovery, fir truths to truths, each justly admired when new, then rightly used as old, was closed in a worthy consistent manner, by a truth which is the most wor admiration, because it includes all the researches preceding ages of Astronomy.

We may take another example of a succession this kind from the history of a science, which, tho it has made wonderful advances, has not yet reac its goal, as physical astronomy appears to have d but seems to have before it a long prospect of fut progress, I now refer to Chemistry, in which I s try to point out how the preceding discoveries affor the materials of the succeeding; although this su dination and connexion is, in this case, less familia men's minds than in Astronomy, and is, perhaps, n difficult to present in a clear and definite shape. vius saw, in the facts which occur, when an acid an alkali are brought together, the evidence that t neutralize each other. But cases of neutralization, acidification, and many other effects of mixture of ingredients of bodies, being thus viewed as facts, ha aspect of unity and law given them by Geoffroy Bergman, who introduced the conception of the Ch cal Affinity or Elective Attraction, by which cer elements select other elements, as if by prefere That combustion, whether a chemical union or a ch cal separation of ingredients, is of the same nature acidification, was the doctrine of Beccher and St and was soon established as a truth which must for part of every succeeding physical theory. That rules of affinity and chemical composition may inc gaseous elements, was established by Black and Ca dish. And all these truths, thus brought to ligh

chemical discoverers,-affinity, the identity of acidification and combustion, the importance of gaseous elements,-along with all the facts respecting the weight of ingredients and compounds which the balance disclosed, were taken up, connected, and included as particulars in the oxygen theory of Lavoisier. Again, the results of this theory, and the quantity of the several ingredients which entered into each compound— (such results, for the most part, being now no longer mere theoretical speculations, but recognized facts)were the particulars from which Dalton derived that wide law of chemical combination which we term the Atomic Theory. And this law, soon generally accepted among chemists, is already in its turn become one of the facts included in Faraday's Theory of the identity of Chemical Affinity and Electric Attraction.

It is unnecessary to give further exemplifications of this constant ascent from one step to a higher;-this perpetual conversion of true theories into the materials of other and wider theories. It will hereafter be our business to exhibit, in a more full and formal manner, the mode in which this principle determines the whole scheme and structure of all the most exact sciences. And thus, beginning with the facts of sense, we gradually climb to the highest forms of human knowledge, and obtain from experience and observation a vast collection of the most wide and elevated truths.

There are, however, truths of a very different kind, to which we must turn our attention, in order to pursue our researches respecting the nature and grounds of our knowledge. But before we do this, we must notice one more feature in that progress of science which we have already in part described.

CHAPTER II.

OF TECHNICAL TERMS.

I.

T has already been stated that we gather knowledge from the external world, when we are able to apply, to the facts which we observe, some ideal conception, which gives unity and connexion to multiplied and separate perceptions. We have also shown that our conceptions, thus verified by facts, may themselves be united and connected by a new bond of the same nature; and that man may thus have to pursue his way from truth to truth through a long progression of discoveries, each resting on the preceding, and rising above it.

Each of these steps, in succession, is recorded, fixed, and made available, by some peculiar form of words; and such words, thus rendered precise in their meaning, and appropriated to the service of science, we may call Technical Terms. It is in a great measure by inventing such Terms that men not only best express the discoveries they have made, but also enable their followers to become so familiar with these discoveries, and to possess them so thoroughly, that they can readily use them in advancing to ulterior generalizations.

Most of our ideal conceptions are described by exact and constant words or phrases, such as those of which we here speak. We have already had occasion to employ many of these. Thus we have had instances of technical Terms expressing geometrical conceptions, as Ellipsis, Radius Vector, Axis, Plane, the Proportion of the Inverse Square, and the like. Other Terms have described mechanical conceptions, as Accelerating Force and Attraction. Again, chemistry exhibits (as do all sciences) a series of Terms which mark the steps of our