Science, whose aim and end is to prove the harmony and "eternal fitness of things," also proves that we live in a world of paradoxes; and that existence itself is a whirl of contradictions. Light and darkness, truth and falsehood, virtue and vice, the negative and positive poles of galvanic or magnetic mysteries, are evidences of all-pervading antitheses, which, acting like the good and evil genii of Persian Mythology, neutralize each other's powers when they come into collision. It is the office of science to solve these mysteries. The appropriate symbol of the lecture-room is a Sphinx; for a scientific lecturer is but a better sort of unraveler of riddles.

Who would suppose, for instance, that water—which every body knows, extinguishes fire—may, under certain circumstances, add fuel to flame, so that the "coming man," who is to "set the Thames on fire," may not be far off. If we take some mystical gray-looking globules of potassium (which is the metallic basis of common pearl-ash) and lay them upon water, the water will instantly appear to ignite. The globules will swim about in flames, reminding us of the "death-fires" described by the Ancient Mariner, burning "like witches' oil" on the surface of the stagnant sea. Sometimes even, without any chemical ingredient being added, fire will appear to spring spontaneously from water; which is not a simple element, as Thales imagined, when he speculated upon the origin of the Creation, but two invisible gases—oxygen and hydrogen, chemically combined. During the electrical changes of the atmosphere in a thunder-storm, these gases frequently combine with explosive violence, and it is this combination which takes place when "the big rain comes dancing to the earth." These fire-and-water phenomena are thus accounted for; certain substances have peculiar affinities or attractions for one another; the potassium has so inordinate a desire for oxygen, that the moment it touches, it decomposes the water, abstracts all the oxygen, and sets free the hydrogen or inflammable gas. The potassium, when combined with the oxygen, forms that corrosive substance known as caustic potash, and the heat, disengaged during this process, ignites the hydrogen. Here the mystery ends; and the contradictions are solved; Oxygen and hydrogen when combined, become water; when separated the hydrogen gas burns with a pale, lambent flame. Many of Nature's most delicate deceptions are accounted for by a knowledge of these laws.

Your analytical chemist sadly annihilates, with his scientific machinations, all poetry. He bottles up at pleasure the Nine Muses, and proves them—as the fisherman in the Arabian Nights did the Afrite—to be all smoke. Even the Will-o'-the-Wisp can not flit across its own morass without being pursued, overtaken, and burnt out by this scientific detective policeman. He claps an extinguisher upon Jack-o'-Lantern thus: He says that a certain combination of phosphorus and hydrogen, which rises from watery marshes, produces a gas called phosphureted hydrogen, which ignites spontaneously the moment it bubbles up to the surface of the water and meets with atmospheric air. Here again the Ithuriel wand of science dispels all delusion, pointing out to us, that in such places animal and vegetable substances are undergoing constant decomposition; and as phosphorus exists under a variety of forms in these bodies, as phosphate of lime, phosphate of soda, phosphate of magnesia, &c., and as furthermore the decomposition of water itself is the initiatory process in these changes, so we find that phosphorus and hydrogen are supplied from these sources; and we may therefore easily conceive the consequent formation of phosphureted hydrogen. This gas rises in a thin stream from its watery bed, and the moment it comes in contact with the oxygen of the atmosphere, it bursts into a flame so buoyant, that it flickers with every breath of air, and realizes the description of Goethe's Mephistopheles, that the course of Jack-o'-Lantern is generally "zig-zag."

Who would suppose that absolute darkness may be derived from two rays of light! Yet such is the fact. If two rays proceed from two luminous points very close to each other, and are so directed as to cross at a given point on a sheet of white paper in a dark room, their united light will be twice as bright as either ray singly would produce. But if the difference in the distance of the two points be diminished only one-half, the one light will extinguish the other, and produce absolute darkness. The same curious result may be produced by viewing the flame of a candle through two very fine slits near to each other in a card. So, likewise, strange as it may appear, if two musical strings be so made to vibrate, in a certain succession of degrees, as for the one to gain half a vibration on the other, the two resulting sounds will antagonize each other and produce an interval of perfect silence. How are these mysteries to be explained? The Delphic Oracle of science must again be consulted, and among the high priests who officiate at the shrine, no one possesses more recondite knowledge, or can recall it more instructively than Sir David Brewster. "The explanation which philosophers have given," he observes, "of these remarkable phenomena, is very satisfactory, and may easily be understood. When a wave is made on the surface of a still pool of water by plunging a stone into it, the wave advances along the surface, while the water itself is never carried forward, but merely rises into a height and falls into a hollow, each portion of the surface experiencing an elevation and a depression in its turn. If we suppose two waves equal and similar, to be produced by two separate stones, and if they reach the same spot at the same time, that is, if the two elevations should exactly coincide, they would unite their effects, and produce a wave twice the size of either; but if the one wave should be put so far before the other, that the hollow of the one coincided with the elevation of the other, and the elevation of the one with the hollow of the other, the two waves would obliterate or destroy one another; the elevation, as it were, of the one filling up half the hollow of the other, and the hollow of the one taking away half the elevation of the other, so us to reduce the surface to a level. These effects may be exhibited by throwing two equal stones into a pool of water; and also may be observed in the Port of Batsha, where the two waves arriving by channels of different lengths actually obliterate each other. Now, as light is supposed to be produced by waves or undulations of an ethereal medium filling all nature, and occupying the pores of the transparent bodies; and as sound is produced by undulations or waves in the air: so the successive production of light and darkness by two bright lights, and the production of sound and silence by two loud sounds, may be explained in the very same manner as we have explained the increase and obliteration of waves formed on the surface of water."

The apparent contradictions in chemistry are, indeed, best exhibited in the lecture-room, where they may be rendered visible and tangible, and brought home to the general comprehension. The Professor of Analytical Chemistry, J.H. Pepper, who demonstrates these things in the Royal Polytechnic Institution, is an expert manipulator in such mysteries; and, taking a leaf out of his own magic-book, we shall conjure him up before us, standing behind his own laboratory, surrounded with all the implements of his art. At our recent visit to this exhibition we witnessed him perform, with much address, the following experiments: He placed before us a pair of tall glass vessels, each filled, apparently, with water; he then took two hen's eggs, one of these he dropped into one of the glass vessels, and, as might have been expected, it immediately sank to the bottom. He then took the other egg, and dropped it into the other vessel of water, but, instead of sinking as the other had done, it descended only half way, and there remained suspended in the midst of the transparent fluid. This, indeed, looked like magic—one of Houdin's sleight-of-hand performances—for what could interrupt its progress? The water surrounding it appeared as pure below as around and above the egg, yet there it still hung like Mahomet's coffin, between heaven and earth, contrary to all the well-established laws of gravity. The problem, however, was easily solved. Our modern Cagliostro had dissolved in one half of the water in this vessel as much common salt as it would take up, whereby the density of the fluid was so much augmented that it opposed a resistance to the descent of the egg after it had passed through the unadulterated water, which he had carefully poured upon the briny solution, the transparency of which, remaining unimpaired, did not for a moment suggest the suspicion of any such impregnation. The good housewife, upon the same principle, uses an egg to test the strength of her brine for pickling.

Every one has heard of the power which bleaching gas (chlorine) possesses in taking away color, so that a red rose held over its fumes will become white. The lecturer, referring to this fact, exhibited two pieces of paper; upon one was inscribed, in large letters, the word "Proteus;" upon the other no writing was visible; although he assured us the same word was there inscribed. He now dipped both pieces of paper in a solution of bleaching-powder, when the word "Proteus" disappeared from the paper upon which it was before visible; while the same word instantly came out, sharp and distinct, upon the paper which was previously a blank. Here there appeared another contradiction: the chlorine in the one case obliterating, and in the other reviving the written word; and how was this mystery explained? Easily enough! Our ingenious philosopher, it seems, had used indigo in penning the one word which had disappeared; and had inscribed the other with a solution of a chemical substance, iodide of potassium and starch; and the action which took place was simply this: the chlorine of the bleaching solution set free the iodine from the potassium, which immediately combined with the starch, and gave color to the letters which were before invisible. Again—a sheet of white paper was exhibited, which displayed a broad and brilliant stripe of scarlet—(produced by a compound called the bin-iodide of mercury)—when exposed to a slight heat the color changed immediately to a bright yellow, and, when this yellow stripe was crushed by smartly rubbing the paper, the scarlet color was restored, with all its former brilliancy. This change of color was effected entirely by the alteration which the heat, in the one case, and the friction, in the other, produced in the particles which reflected these different colors; and, upon the same principle, we may understand the change of the color in the lobster-shell, which turns from black to red in boiling; because the action of the heat produces a new arrangement in the particles which compose the shell.

With the assistance of water and fire, which have befriended the magicians of every age, contradictions of a more marvelous character may be exhibited, and even the secret art revealed of handling red-hot metals, and passing through the fiery ordeal. If we take a platinum ladle, and hold it over a furnace until it becomes of a bright red heat, and then project cold water into its bowl, we shall find that the water will remain quiescent and give no sign of ebullition—not so much as a single "fizz;" but, the moment the ladle begins to cool, it will boil up and quickly evaporate. So also, if a mass of metal, heated to whiteness, be plunged in a vessel of cold water, the surrounding fluid will remain tranquil so long as the glowing white heat continues; but, the moment the temperature falls, the water will boil briskly. Again—if water be poured upon an iron sieve, the wires of which are made red hot, it will not run through; but, on the sieve cooling, it will run through rapidly. These contradictory effects are easily accounted for. The repelling power of intense heat keeps the water from immediate contact with the heated metal, and the particles of the water, collectively, retain their globular form; but, when the vessel cools, the repulsive power diminishes, and the water coming into closer contact with the heated surface its particles can no longer retain their globular form, and eventually expand into a state of vapor. This globular condition of the particles of water will account for many very important phenomena; perhaps it is best exhibited in the dew-drop, and so long as these globules retain their form, water will retain its fluid properties. An agglomeration of these globules will carry with them, under certain circumstances, so much force that it is hardly a contradiction to call water itself a solid. The water-hammer, as it is termed, illustrates this apparent contradiction. If we introduce a certain quantity of water into a long glass tube, when it is shaken, we shall hear the ordinary splashing noise as in a bottle; but, if we exhaust the air, and again shake the tube, we shall hear a loud ringing sound, as if the bottom of the tube were struck by some hard substance—like metal or wood—which may fearfully remind us of the blows which a ship's side will receive from the waves during a storm at sea, which will often carry away her bulwarks.

It is now time to turn to something stronger than water for more instances of chemical contradictions. The chemical action of certain poisons (the most powerful of all agents), upon the human frame, has plunged the faculty into a maze of paradoxes; indeed, there is actually a system of medicine, advancing in reputation, which is founded on the principle of contraries. The famous Dr. Hahnemann, who was born at Massieu in Saxony, was the founder of it, and, strange to say, medical men, who are notorious for entertaining contrary opinions, have not yet agreed among themselves whether he was a very great quack or a very great philosopher. Be this as it may, the founder of this system, which is called Homoeopathy, when translating an article upon bark in Dr. Cullen's Materia Medica, took some of this medicine, which had for many years been justly celebrated for the cure of ague. He had not long taken it, when he found himself attacked with aguish symptoms, and a light now dawned upon his mind, and led him to the inference that medicines which give rise to the symptoms of a disease, are those which will specifically cure it, and however curious it may appear, several illustrations in confirmation of this principle were speedily found. If a limb be frost-bitten, we are directed to rub it with snow; if the constitution of a man be impaired by the abuse of spirituous liquors, and he be reduced to that miserable state of enervation when the limbs tremble and totter, and the mind itself sinks into a state of low muttering delirium, the physician to cure him must go again to the bottle and administer stimulants and opiates.

It was an old Hippocratic aphorism that two diseases can not co-exist in the same body, wherefore, gout has actually been cured by the afflicted person going into a fenny country and catching the ague. The fatality of consumption is also said to be retarded by a common catarrh; and upon this very principle depends the truth of the old saying, that rickety doors hang long on rusty hinges. In other words, the strength of the constitution being impaired by one disease has less power to support the morbid action of another.

We thus live in a world of apparent contradictions; they abound in every department of science, and beset us even in the sanctuary of domestic life. The progress of discovery has reconciled and explained the nature of some of them; but many baffle our ingenuity, and still remain involved in mystery. This much, however, is certain, that the most opposed and conflicting elements so combine together as to produce results, which are strictly in unison with the order and harmony of the universe.