This arrangement in the present state of our knowledge is excellent, particularly as it separates the certain from the doubtful, the known from the unknown, the established truths of science and generalizations of facts from speculative views and analogical reasonings.

It is not our intention to enter into a minute analysis of this work, but to consider the striking features which give it character, and the new and general doctrines which it contains., When we compare what chymistry is at present with what it was fifty years ago, we are filled with astonishment. The German philosophy was then the fashion of the times, and the German school was at the height of its glory. A few substances only were known, and those very vaguely; the number of the ancient metals was indeed somewhat enlarged, but the chymises of those days had not learnt to distinguish the different kinds of earths, and they were not at all acquainted with the different kinds of gasses. They called all the airs they met with factitious airs, and conceived them to be all merely different modifications of the air of the atmosphere. Statics had not been brought into the laboratory. The great agent was fire; and the "philosophers by fire" let the gasses, or spirits, as they were called, escape in their experiments, and rejected the fixed residue, the "caput mortuum," as useless. By means of a few elements borrowed jointly from the Greeks and the alchymists, with the assistance of their main spring phlogiston, they were able to explain in a manner satisfactory to themselves all the changes in art, and all the grand operations in nature-and they were contented. Such nearly was the state of the science when Dr. Black discovered the existence of carbonic acid gas; a discovery which may be truly said to have given wings to chymistry. It at once demonstrated that prevalent opinion to be erroneous which supposed the existence of only one species of elastic fluid, and rendered it more than probable that what had been neglected under the title of factitious airs, were distinct and peculiar gasses. The light which from this one discovery burst upon all departments of chymistry, rosed the zeal of inquirers in this country to the investigation of gaseous bodies, and their were rewarded with the most brilliant success. Cavendish, by the discovery of hydrogen, and of the composition of water and nitric acid, and Priestley, by the discovery of nitrous gas, nitrous oxide, and the composition of the atmosphere, obtained, as it were, the keys of nature's laboratory. Black, Cavendish, Priestley, were the founders of pneumatic chymistry, and may with propriety even be called the founders

labours

of the science of chymistry; inasmuch as these active inves tigators, and pre-eminently among them Mr. Cavendish, first introduced weights and measures, and applied them for the establishment of chymical truth. The development of the doctrines of latent heat by Black, the analytic labours of Scheele and Bergmann, and the generalization of facts by Lavoisier, constituted the first stage of modern chymistry.

Let us pause a moment to consider the character of the last-mentioned philosopher, who formed a party and a school, and left a proud name behind him in this department of science. The merit of Lavoisier was that of a sound logician, not of a discoverer. He was strongly impressed with the importance of keeping the imagination under the discipline of experiment; that nothing must be taken for granted, nothing admitted to exist that is not made evident to the senses; that occult causes, and unknown bodies, and all the remains of scholastic trifling and alchymical mysticism should be banished from the new philosophy; that truth was to be reached by the road of induction, and that scientific principles must be acquired from the comparison and expansion of individual facts. To make one proposition of the whole, that all bodies are to be considered as simple substances, which have not yet been decompounded. The defective part of his great design was the French nomenclature, which, though admirably adapted to a perfect science, was not at all suited to one in its infancy. It was a tight garment that did not admit of enlargement, well fitted to the man, but very unfavourable to the growing child.

After the discovery of the Leyden phial, in 1746, electricity became a subject both of popular and scientific attention. It was next to a miracle that an invisible power of such an extraordinary nature, as to be capable of melting the hardest metals, producing all the phenomena of light and fire, and destroying even animal life itself, should be confinable in a glass vessel, and subject to be arrested in its progress by silk. Neither was the interest in electricity diminished by the labours of Franklin, who identified it with the lightning of heaven, and by the simplest means, by a school-boy's kite, realized the fable of antiquity respecting the Promethean theft. In the progress of inquiry, fresh wonders were added to electricity. The lightning of the thunder-storm was found to be wielded by some of the inhabitants of the deep: the gymnotus, the silurus, the torpedo, were proved to be armed with this power, and capable of voluntarily employing it as a weapon of attack or defence. But still electricity was

unconnected with chymistry, and remained an insulated science, being analogous to nothing but magnetism.

In 1800, the first step was taken to connect the two sciences by the great discovery of the pile of Volta. This instrument, whilst in action, might be compared with an inexhaustible Leyden phial, always capable of giving shocks, of producing the phenomena of heat and light, and of operating various chymical changes of an extraordinary kind. It decomposed water and acids, and metallic salts, and, what is very remarkable, the separated elements of water were not evolved together, but maintained their distinct places; the hydrogen at the part determined to be the negative extremity, and the oxygen at the positive end. The power, too, was found identical with common electricity, differing merely in degree, not in kind, and just the same as that possessed by the torpedo. Like common electricity, it gave the shock, produced heat and light, melted metals, and passed imperceptibly over their surfaces; was stopped by glass, silk, and similar substances, and might be transferred to a glass jar, and there confined. We need not state that common electricity was found capable of producing similar chymical changes.

To no one is Voltaic electricity so much indebted as to Sir H. Davy for the discovery of its principles of action, and for the application of it, as an instrument of research, to chymical analysis. He detected the errors of Pacchioni and Sylvester, who had asserted that, by the operation of electricity, muriatic acid and fixed alkali were formed on the decomposition of water; and he exploded their notions, that the muriatic, oxymuriatic, and nitric acids, as well as the volatile and fixed alkalies were all of similar origin, and merely different oxides of hydrogen. He proved that the alkalies and acids they had supposed to be generated, were previously existing in the substances employed in the experiments, and only produced. He proved, at the same time, that the decomposing powers of the Voltaic battery are so energetic, that the firmest rocks, the hardest minerals, and most vehement chymical affinities, are incapable of resisting them, and that the smallest quantities are within the scope of its power. He thus drew out from rocks and salts, from animal and vegetable substances, their constituent parts, and detected some of their minutest ingredients. He determined various laws respecting electrical action and chymical decomposition; as, that inflammable and metallic substances, that earths, alkalies, and metallic oxides, are attracted by the negative extremity or pole of the battery, being themselves positive; that oxygen, chlorine, and acids, are attracted by the positive pole, because they themselves are

negative; that chymical attractions are put to rest or destroyed by superior electrical attractions; and that bodies may be transferred, without interruption, from one pole to another even through fluids, having naturally a strong chymical attraction for them. These views, which first appeared in his publications in the Philosophical Transactions, are again developed and illustrated in his "Elements of Chymical Philosophy," together with the theory of the action of the Voltaic battery; which action he does not attribute primarily to chymical changes, but to the contact of the different metals and fluids.

The more clearly to convey a notion of his theory, we shall have recourse, as he has done, to the common electrical machine. When a body that is a non-conductor is brought into the neighbourhood of the prime conductor, it acquires two electrical states, or "polarities," as our author expresses it: the negative one is that nearest the positive conductor; the: positive one is that most remote. The same occurs in respect to the Voltaic battery, when pieces of steel wire are placed in water; connected with a powerful combination, they separately acquire polarities, as if they were influenced by a powerfulmagnet; they arrange themselves with their positive poles farthest from the positive pole of the battery, and the negative nearest, and they acquire similar powers of chymical decomposition. These facts are readily applicable to the action of the battery. The battery does not differ from the electrified wires, but in having within itself the source of its own electricity, instead of possessing a borrowed power. Each pair of metals is analogous to one wire; one of the pair is positive, the other negative. Sir H. Davy supposes the water to be capable. of becoming electrically polar, and one part of it, viz. that extremity of a particle which is nearest the positive metal acquires negative polarity, and the other part, in consequence, acquires positive polarity; while the different series of metals so influence each other, that the power of the whole combination increases with the number and surface of the plates.

Though electrical action is not primarily dependent on chymical changes, as the early inquirers imagined, yet are they intimately connected, as appears from the impossibility: of preserving a permanent action of the battery without the assistance of chymical agents, and from the circumstance that those substances excite the battery most powerfully which act on the metals most rapidly. The explanation offered by Sir H. Davy is, that the tendency of electrical action is to return to its equilibrium; and that the tendency of chymical action is to destroy this equilibrium. Thus, when a commu

nication is made between the negative and positive cylinders of a common electrical machine, there is an immediate rest, or cessation, of all action; and in a similar way the Voltaic battery would cease to act when its extremities are joined, were it not for the chymical changes taking place: oxygen and chlorine, and acids themselves negative bodies, are attracted by the positive metallic surfaces, and hydrogen and alkalies themselves positive, are attracted by the negative metallic surfaces; those individuals capable of entering into combination with the metals, unite with them, and the electrical equilibrium is momentarily restored; but the combinations formed being soluble in the water, are removed from the metals; and the gasses evolved, being thus disengaged, the equilibrium of electricity is again disturbed, and the electrical action continued.

Our author, in a satisfactory manner, accounts for the fact, that the action of a battery, on imperfect conductors, such as water, the human body, and similar substances, increases with the number of plates; whilst its action on perfect conductors increases with the size of the plates. Those imperfect conductors, it is said, can only discharge a very minute quantity of electricity, probably not more than the smallest battery possesses; therefore, they are only affected by a difference of intensity, and the greater the intensity of the electricity is, the more they are affected; but the intensity or the energy of the electrical polarities is independent of quantity of surface, and is proportionable only to the number of pairs of plates. On the other hand, the perfectly conducting metals are capable of discharging large quantities of electricity, consequently, they are affected by the quantity; and as the quantity is proportionable to the surface, the effect of a battery, on perfect conductors, will be proportionate to the surface. These important principles Sir H. Davy has explained at length in his Elements, and proved and illustrated the hypothesis by a series of happy experiments. He has endeavoured to deter mine the exact ratio in which the intensity of the battery, and the quantity of electricity, increase with the number of similar plates, and also the ratio of increase of quantity, with the increased size of the plates. And from experiments apparently admitting of much accuracy, he concludes, that the intensity of the battery is as the square of the number;—that the quantity of electricity is as the number of equal plates;

but that the quantity or power of acting on perfect conductors is in a very high ratio with the increased surface, probably higher than even the square.

Sir H. Davy observes, that "electrical effects are exhibited VOL. I. New Series. 30