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the whole with exact references to the original works, in which the discoveries have been registered.

"A System of Chemistry, by J. Murray," in 4 vols. 8vo. To which there is added a very valuable Supplement, containing a view of the recent discoveries in the science. The leading feature of this system, is the attention shewn to the general doctrines of chemistry, which the author has reviewed and illustrated in as ample a manner as possible, under the conviction, that the most important object to which the attention of those undertaking its study can be directed, is that relating to the principles by which its individual facts are connected and arranged, because, without an intimate knowledge of these, the science is not acquired; and the acquisition of such knowledge, at once facilitates, and renders more interesting the prosecution of its minute details and applications.

On a smaller scale is "A System of theoretical and practical Chemistry," in 2 vols. by Frederic Accum. In these volumes, the author assumes that the reader is unacquainted with the science, and has accordingly been very minute in his directions for the repetition of experiments.

"Elements of Chemistry, &c." by M. Lavoisier, translated into English by Mr. Kerr. Notwithstanding the various improvements and important discoveries which have been made since the death of the illustrious author of these Elements, his work will afford much satisfaction to every person who makes this science his pursuit.

To these may be added, and which ought to have been noticed under the article Electricity:

"Elements of Electricity and Electro-Chemistry, by George Singer."

"Practical Electricity and Galvanism, containing a Series of Experiments, calculated for the Use of those who are desirous of becoming acquainted with that Branch of Science, by John Cuthbertson." Both these works are illustrated with plates, and are extremely well adapted for the purposes expressed in the titles.

CHAP. VIII.

NATURAL HISTORY.

Natural History-Method of Classification-The three kingdoms of nature. MINERALOGY Connected with Chemistry-Different systems, viz. that of Pott-Gmelin-Cronstedt-Werner-Brochant-Hauy-BrongniartRome de Lisle, Explanation of Werner's method-Authors: Jameson

-Kirwan-Hany-Brochant-Klaproth-Aikin.

and Neptunian Theories. Bakewell.

GEOLOGY-Plutonic

NATURAL HISTORY, taken in its most extensive sense, signifies a knowledge and description of the whole universe, and of the several parts of which it is composed. According to this definition, the science is as extensive as nature itself; but in a more appropriate and limited sense, and to this we must necessarily confine ourselves, it treats of those substances of .which the earth is composed, and of those organized bodies, whether vegetable or animal, which adorn its surface, soar into the air, or dwell in the bosom of the waters. In this restricted sense, natural history may be divided into two heads: the first teaches us the characteristics, or distinctive marks of each individual object, whether mineral, vegetable, or animal; the second renders us acquainted with all its peculiarities, in respect to its habits, its qualities, and its uses. To facilitate the attainment of the first, it is necessary to

adopt some system of classification, in which the individuals, that correspond in particular points, may be arranged together: hence, in the artificial system of Linnæus, and other writers on the subject, we have species, genera, orders, classes, and kingdoms.

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The grand division of natural objects commonly adopted, is into three kingdoms, the mineral, vegetable, and animal kingdoms, because it is thought to be perfectly consistent with nature, and because, at first sight, some writers have thought it so clear and distinct, as to be almost impossible to make a mistake in referring any particular object to its proper kingdom. This arises from their having noticed only such objects as bear evident marks of the division to which they belong; but on more accurate observation, it will be found, that there are not only individuals, whose real characteristics it is difficult to ascertain, but that there is likewise one whole class of productions, called zoophytes by naturalists, which seem, indeed, to form the connecting links between the different kingdoms. They are animals of the polypus kind, mostly covered with a calcareous crust, differing little in composition from the shells of lobsters, shrimps, and other shell-fish, and formed like them from an exudation, or secretion, on the surface of their bodies. These polypi are connected together by thousands, or even millions, and assume a great variety of appearances according to their arrangement: the same species, however, always assuming the same, or very nearly the same appearance. Some are connected together in form of a stem and branches, as the flustræ, sertulariæ, corallines and others; many of which have their offspring in the egg-state attached to them, and so situated as to bear an exact resemblance to the seed-vessels of plants. These are altogether so like to many of the sea-plants, as to be generally confounded with them, under the title of sea-weeds; but the attentive naturalist may, by examining them in their natural state, perceive the tentacula or feelers of each polypus extended in its search for food, and hastily retracting within its shell upon the least alarm. Many

of this description are found attached to oysters or other shellfish; and often to stones and pebbles, which are covered, or occasionally wetted by the sea.

"Other zoophytes assume less regular figures, and are much more firm and solid, resembling the productions of the mineral kingdom. Madrepores and millepores, called often brainstones, are of this kind. At first sight they look very like stones and pebbles, or like pieces of chalk or marble; but on an accurate inspection, any one may perceive marks of an organic structure; and when they are in a recent state, may detect the inhabitants of their numerous cells."

Of the three grand divisions of nature, the animal kingdom stands highest in the scale; then the vegetable; and, lastly, the mineral kingdom. We shall begin with the lowest, and ascend to the highest; and we may observe, that minerals differ from vegetables and animals, in being produced fortuitously, growing by external secretion, and being only capable of destruction by mechanical or chemical force; while the other two are produced by generation, grow by nutrition, and are destroyed by death. While animals and vegetables thus agree in their general characters, they also possess features of marked distinction; but they both agree in an origin by generation, growth by nutrition, and a termination by death. In an organized structure, and an internal living principle, they differ in the power with which the living principle is endowed, and the effects that it is capable of exerting. In vegetables it is limited, as far as we know, to the properties of mere irritability and contractility: in the animal it superadds to these properties those of muscularity, sensation, and voluntary motion.

Mineralogy is that science which teaches us the properties of mineral bodies; and by which we learn to characterize, distinguish, and class them into a proper order. It seems to have been in a manner coeval with the world. Precious stones of various kinds appear to have been known and valued among the Jews and Egyptians in the time of Moses, and the most rude and barbarous nations seem to have had some

knowledge of the ores of different metals. Mineralogy, as a science, is connected with chemistry, and must advance with that to perfection. The practical mineralogist will not content himself with classing the substances connected with his study, merely by inspecting the outward appearance; but will dive deeper, by decomposing them according to the rules of chemistry. This method was carried a considerable way towards perfection, by M. J. H. Pott, a celebrated German chemist; whose works, "De Sulphuribus Metallorum," and "Observationes circa Sal," published about the middle of the last century, were very highly esteemed. Pott arranged earthy minerals according to their proportions of ingredients; but his four great classes, are the Alkaline, Siliceous, Argillaceous and Gypseous. An early death prevented this philosopher from extending his inquiries to the metals.

Cronstedt, the Swedish mineralogist, who was some years posterior to Pott, greatly improved upon his method. The system of Cronstedt was published in 1758, and for twenty years was generally received by the scientific world. In 1780, a translation of Cronstedt's mineral system appeared in Germany, accompanied with notes, by Werner, the Professor of Mineralogy, at Freyberg, in Saxony. Six years before, the professor had published a separate treatise on the classification of minerals, in which he exhibited much skill in a method of describing them by means of external characters. Cronstedt divided all mineral substances into four classes, viz. Terræ, Salia, Phlogistica, and Metalla. One of the most striking excellencies of Cronstedt's system, is the strict adherence to a fixed principle as the basis of classification; it is throughout chemical; and the principles on which the orders and genera are founded, are still much followed by chemical mineralogists. The compound rocks and petrifactions, which had been included in the mineral system of Linnæus and others, were by Cronstedt described in an appendix.

The system of Linnæus, just alluded to, was first published in 1736, and in an improved edition in 1768; but this is

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