ters of such motions in verse. The rule of natural Principium tepeat, medium cum fine calebit. Principium fervet, medium calet, ultima friget. It appears to have been considered by Aristotle a difficult problem to explain why a stone thrown from the hand continues to move for some time, and then stops. If the hand was the cause of the motion, how could the stone move at all when left to itself? if not, why does it ever stop? And he answers this difficulty by saying, "that there is a motion communicated to the air, the successive parts of which urge the stone onwards; and that each part of this medium continues to act for some while after it has been acted on, and the motion ceases when it comes to a particle which cannot act after it has ceased to be acted on." It will be readily seen that the whole of this difficulty, concerning a body which moves forwards and is retarded till it stops, arises from ascribing the retardation, not to the real cause, the surrounding resistances, but to the body itself, to which the common forms of language attribute it, as the nominative of the verb "move." One of the doctrines which was the subject of the warmest discussion between the defenders and 13 Alsted. Encyc. tom i. p. 687. 14 Phys. Ausc. viii. 10. opposers of Aristotle, at the revival of physical knowledge, was that in which he asserts 15" That body is heavier than another which in an equal bulk moves downward quicker." The opinion maintained by the Aristotelians at the time of Galileo was, that bodies fall quicker exactly in proportion to their weight. The master himself asserts this in express terms, and reasons upon it". Yet in another passage he appears to distinguish between weight and actual motion downwards". "In physics, we call bodies heavy and light from their power of motion; but these names are not applied to their actual operations (eveрyears) except any one thinks momentum (poжη) to be a word of both applications. But heavy and light are, as it were, the embers or sparks of motion, and therefore proper to be treated of here." The distinction just alluded to between power or faculty of action, and actual operation or energy, is one very frequently referred to by Aristotle; and though not by any means useless, may easily be so used as to lead to mere verbal refinements instead of substantial knowledge. The Aristotelian distinction of causes has not any very immediate bearing upon the parts of physics of which we have here mainly spoken; but it was so extensively accepted, and so long retained, that it may be proper to notice it. "One kind of 15 De Cœlo, iv. 1, p. 308. 16 De Cœlo, iii. 2. 18 Phys. ii. 3. cause is the matter of which any thing is made, as bronze of a statue, and silver of a phial; another is the form and pattern, as the cause of an octave is the ratio of two to one; again, there is the cause which is the origin of the production, as the father of the child; and again, there is the end, or that for the sake of which anything is done, as health is the cause of walking." These four kinds of cause, the material, the formal, the efficient, and the final, were long leading points in all speculative inquiries; and our familiar forms of speech still retain traces of the influence of this division. It is my object here to present to the reader in an intelligible shape, the principles and mode of reasoning of the Aristotelian philosophy, not its results. If this were not the case, it would be easy to excite a smile by insulating some of the passages which are most remote from modern notions. will only mention, as specimens, two such passages, both very remarkable. I In the beginning of the book "On the Heavens," he proves" the world to be perfect, by reasoning of the following kind: "The bodies of which the world is composed are solids, and therefore have three dimensions; now three is the most perfect number; it is the first of numbers, for of one we do not speak as a number; of two we say both; but three is the first number of which we say all; moreover, it has a beginning, a middle, and an end." 19 De Cœlo, i. l. The reader will still perceive the verbal foundations of opinions thus supported. "The simple elements must have simple motions, and thus fire and air have their natural motions upwards, and water and earth have their natural motions downwards; but besides these motions, there is motion in a circle, which is unnatural to these elements, but which is a more perfect motion than the other, because a circle is a perfect line, and a straight line is not; and there must be something to which this motion is natural. From this it is evident," he adds, with obvious animation, "that there is some essence of body different from those of the four elements, more divine than those, and superior to them. If things which move in a circle move contrary to nature, it is marvellous, or rather absurd, that this, the unnatural motion, should alone be continuous and eternal; for unnatural motions decay speedily. So that from all this, we must collect, that besides the four elements which we have here and about us, there is another removed far off, and the more excellent in proportion as it is more distant from us." This fifth element was the quinta essentia" of after writers, of which we have a trace in our modern literature, in the word quint 66 essence. Sect. 3.—Technical Forms of the Greek Schools. WE have hitherto considered only the principle of the Greek Physics; which was, as we have seen, to deduce its doctrines by an analysis of the notions which common language involves. But though the Grecian philosopher began by studying words in their common meanings, he soon found himself led to fix upon some special shades or applications of these meanings as the permanent and standard notion, which they were to express; that is, he made his language technical. The invention and establishment of technical terms is an important step in any philosophy, true or false; we must, therefore, say a few words on this process, as exemplified in the ancient systems. 1. Technical Forms of the Aristotelian Philosophy.We have already had occasion to cite some of the distinctions introduced by Aristotle, which may be considered as technical; for instance, the classification of causes as material, formal, efficient, and final; and the opposition of qualities as absolute and relative. A few more of the most important examples may suffice. An analysis of objects into matter and form, when metaphorically extended from visible objects to things conceived in the most general manner, became an habitual hypothesis of the Aristotelian school. Indeed this metaphor is even yet one of the most significant of those which we can employ, to suggest one of the most comprehensive and fundamental antitheses with which philosophy |