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He maintains that matter is infinitely divisible; that the universe is full, and that there is no vacuum in nature; that the world is eternal; that the sun, which has always revolved as it does at present, will for ever continue to do so; and finally, that the generations of men succeed each other without having had a beginning or foreseeing an end.[Pg 53]
He alleges that the heavens are incapable of decay; and that although sublunar things are subject to corruption, their parts nevertheless do not perish; that they only change place; that from the remains of one thing another is made; and that thus the mass of the world always remains entire. He holds that the earth is in the centre of the world; and that the First Being makes the skies revolve round the earth, by intelligences which are continually occupied with these motions.
He asserts that all of the globe which is now covered by the waters of the sea was formerly dry land; and that what is now dry land will be again converted into water. The reason is this: the rivers and torrents are continually carrying along sand and earth, which causes the shores gradually to advance, and the sea gradually to retire; so that in the course of innumerable ages the alleged vicissitudes necessarily take place. He adds, that in several parts which are considerably inland, and even of great elevation, the sea, when retiring, left shells, and that, on digging in the ground, anchors and fragments of ships are sometimes found. Ovid attributes the same opinion to Pythagoras.
Aristotle farther remarks, that these conversions of sea into land, and of land into sea, which gradually take place in the long lapse of ages, are in a great measure the cause of our ignorance of past occurrences. He adds, that besides this other accidents happen, which give rise even to the loss of the arts; and among these he enumerates pestilences, wars, famines, earthquakes, burnings, and desolations, which exterminate all the inhabitants of a country, excepting a few who escape and save themselves[Pg 54] in the deserts, where they lead a savage life, and where they give origin to others, who in the progress of time cultivate the ground, and invent or rediscover the arts; and that the same opinions recur, and have been renewed times without number. In this manner, he maintains that, notwithstanding these vicissitudes and revolutions, the machine of the world always remains indestructible.
If an apology were necessary for the brevity of the above sketch, it might be urged, that it probably contains all that is authentic respecting the life of this eminent philosopher; and that our object is to condense, not to expand; to direct the attention to characteristic features, not to lead the mind to expatiate vaguely upon the general surface.[Pg 55]
Aristotle's Ideas respecting the Soul—His Views of Anatomy and Physiology—Introduction to his History of Animals, consisting of Aphorisms or general Principles—His Division of Animals; their external Parts; their Arrangement into Families; their internal Organs; Generation, &c.
Of all the sciences, it has been remarked, that which owes most to Aristotle is the natural history of animals. Not only was he acquainted with numerous species, he also described them according to a comprehensive and luminous method, which perhaps none of his successors have approached; arranging the facts observed, not according to the species, but according to the organs and functions, which affords the only means of establishing comparative results. It may in fact be said, that besides being the oldest author on comparative anatomy whose writings we possess, he was likewise one of those who have treated that part of natural history with most genius, and best deserves to be taken as a model. The principal divisions which are still adopted by naturalists in the animal kingdom are those of Aristotle, and he proposed some which have been resumed after having been unjustly rejected. If we examine the foundation of these great labours, we shall find that they all rest on the same method,[Pg 56] which is itself derived from the theory respecting the origin of general ideas. He always observes facts with attention, compares them with great precision, and endeavours to discover the circumstances in which they agree. His style, moreover, is suited to his method: simple, precise, unstudied, and calm, it seems in every respect the reverse of Plato's; but it has also the merit of being generally clear, except in some places where his ideas themselves were not so.[C]
In one of his treatises, Aristotle divides natural bodies into those possessing life, and those destitute of that principle,—into animate and inanimate. He considers soul as the vital energy or vivifying principle common to all organized bodies; but distinguishes in it three species. Thus, in plants there is a vegetative, in animals a vegetative and a sentient, in man a vegetative, a sentient, and a rational soul. The functions of nutrition and generation in plants and animals he attributes to the vegetative soul; sense, voluntary motion, appetite, and passion, to the sentient soul; the exercise of the intellectual faculties, to the rational soul.
His ideas of anatomy and physiology were extremely imperfect. Thus, he supposed the brain to be a cold spongy mass, adapted for collecting and exhaling the superfluous moisture, and intended for aiding the lungs and trachea in regulating the heat of the body. The heart is the seat of the vital fire, the fountain of the blood, the organ of motion, sensation, and nutrition, as well as of the passions, and the origin of the veins and nerves. The blood is confined to the veins; while the arteries contain[Pg 57] an aërial spirit; and by nerves he means tendons, nerves, and arteries,—in short, strings of all kinds, as the name implies. The heart has three cavities; in the larger animals it communicates with the windpipe, or the ramifications of the pulmonary artery receive the breath in the lungs and carry it to the heart. Respiration is performed by the expansion of the air in the lungs, by means of the internal fire, and the subsequent irruption of the external air to prevent a vacuum. Digestion is a kind of concoction or boiling, performed in the stomach, assisted by the heat of the neighbouring viscera.
It is perhaps impossible at the present day, when the investigation of nature is so much facilitated by the accumulated knowledge of ages in every department of physical science, by the commercial relations existing between countries in all parts of the globe, by a tried method of observation, experiment, and induction, and finally, by the possession of the most ingenious instruments, to form any adequate idea of the numerous difficulties under which the ancient naturalist laboured. On the other hand, he had this great advantage, that almost every thing was new; that the most simple observation correctly recorded, the most trivial phenomenon truly interpreted, became as it were his inalienable property, and was handed down to succeeding ages as a proof of his talents,—a circumstance which must have supplied a great motive to exertion.
The History of Animals is undoubtedly one of the most remarkable performances of which physical science can boast. It must not, however, be imagined that it is a work which, replete with truth and exhibiting the well-arranged results of accurate[Pg 58] observation and laborious investigation, is calculated to afford material aid to the modern student. To him more recent productions are the only safe guides; nor is it until he has studied them, and interrogated nature for himself, that he can derive benefit from the perusal of the treatise which we now proceed to examine.