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Light and Its Phenomena

In treating about Light, we must consider it as a fixed means towards a definite end, and not neglect the final cause. The end is to enable animals to feel beyond the extent of their limbs; and the means are the excitement of the universal medium in which the eye and optic nerves are situated. Any fancies or mysteries beyond this, merit but secondary consideration. We find, universally, a convex eye for convergence and increase of action on the nerve, which communicates with the brain. We discover an arrangement of media and forms, which permits concentrated reflections from this outer surface to the retina. And we perceive, that the parallel rays fall with different incidence on every part, so that the continuous convexity being parellel to itself, the rays proceed perpendicularly, and meets the other in a focus common to the whole. This is nature's own adaptation, and it teaches and proscribes our speculations. We have the excited medium, the eye in that medium, and the arrangement to concentrate and multiply the force of the action on the retina, in all eyes of all animated nature; in all which requires feeling or discernment at a distance. We learn, in infancy, to use the eye just as we do the hands and legs. We have a conventional nomenclature for the shades of its impressions, which we call colors; and we learn to distinguish distances, to discriminate forms, and estimate bulks. All these are acquired powers, as much so as the power of playing the violin with the hands. Beyond' light in the abstract, all the rest is art, in which we deal with the most subtle of agencies-first, that of light, and second, the refined discrimination of the nerves.

The science of optics treats of the excitement and its causes, of the powers, properties, and accidents of light, and of the instruments by which we analyse it, and aid the eye in performing more than unassisted nature. In all this we must reason as on other subjects. There is no miracle in the operations; and however subtle, nothing, in point of fact, distinct from matter and motion, and their laws. As the only use of light is to employ the instrument of animal vision, the eye and as the only use of the eye is to concentrate the delicate momenta of light, so we have in this exclusive fitness of each for the other the most unquestionable proof of design in one or both, though nature, in many other instances, affords other proofs as conclusive. Newton supposed light to be a concourse of projectiles, proceeding from the luminous body to that which is illuminated: but this was a mistake of the infancy of enquiry like many other mistakes of that age. According to Huygens, light consists in the undulations of a highly elastic and subtle fluid pervading all bodies, and propagated round the luminous centre in spherical waves. Each point propagates a series of concentric waves, which intersect one another without confusion. In these undulations, the particles, though in continual motion, are not themselves carried along, but receive only such an impulse as they communicate to others, just as sound is propagated through air. But while each particle in which a luminous wave is propagated communicates its motion to the next particle in a straight line, it also communicates a portion of its motion to other particles, so as to create a new spherical undulation of which it is still the general centre; of course also, it assumes that the same medium permeates all bodies, and that their phenomena is their re-action. It should never be forgotten that all light arises from mere combustion or combination of gases. The solar light, in all its properties, so much accords with our lights, that there can be little doubt but the origin of all light is the same. Light, in general, originates in heat, and heat is the first display, while heat is the motion of the radiation of atoms; and, when stopped, heat is created by the transfer of their momenta. When the intensity and flow increases, the radiation affects the medium of space, or substratum of gases; and it then becomes light, and heat and light mingled. In our terrestrial lights, we observe the inflammable principle, hydrogen, combined with some form of carbon, and then the excitement or lighting of this mixture is immediately followed by the fixation of oxygen, and its great heat. The process is accompanied by an extended excitement of the medium in the space, which we call light. The flames of a lamp, candle, coalgas, etc., are exactly of this description. Generally speaking, the color varies with the carbon, the degree of incandescence with the hydrogen, and the intensity with the oxygen. The proportions are definite, for too much or too little of either, renders the result less perfect, An experimentum crucis is afforded by the iron door of a large furnace. As it heats, the flow of heating atoms is at first large, and may be felt as separate blows on the face within 2 or 3 feet. This proceeds till the excitement of the plate creates sub-division enough for red rays, and the door soon becomes red; but before it becomes red all over, the centre being most excited, and producing greater subdivision, passes rapidly through orange and yellow, while the parts around are either red or dark. The yellow, however, spreads, and by the time the whole is red, the centre is white, with a rude display of all the prismatic colors in different parts, till the centre is glowing white, and the whole acquires a color approaching to white. CHEMISTRY.

Chemistry is the science of atoms; it detects their relative powers, their laws of combination, and their means of decomposition. It enables us, in conventional language, to understand the construction of bodies. Beyond all question, the activity of atoms, their actions and reactions, and their astonishing excitements, are derived from the great motions of the earth of 65,000 miles direct, and 1000 deflected and oblique in every hour. We see the effect of the action and reaction of the Moon in the waters, and we may infer, that the great motions have greater power on the divisible solid parts. The action, too, is constant, and has continued for indefinite ages, so that order and system would now characterize every motion and result; and establish a succession of dependence and of activity with perfect harmony. To this primary cause we are also to ascribe correlative actions in the effects which we call electricity, the laws of the diffusion of heat, evaporation, etc., also the definite proportion of kinds of atoms mingled in substances, governed as the whole are by the arithmetic of motion. To the same cause we are also to refer those relative effects on one kind of matter or another, called their antagonist qualities, and all their decomposing and recomposing powers.

The science of Chemistry assumed its modern character in the hands or Beecher and Stahl, residents of Mentz. They first perceived the connection of the atmosphere and of gases, with the production of phenomena, and paved the way for the discoveries of Bergmann and Scheele, two Swedes, who died in 1784 and 1786, and those of Priestley in England, and Lavoisier in France; while Berzelius, another Swede, Fourcroy, Berthollet, and Gay Lussac, in France; Higgins, Dalton, Thompson, Wollaston, Davy, and Faraday, in England, in their days conferred precision on its pursuits, Cavendish, in 1766, discovered hydrogen, Priestley, between 1774 and 1779, discovered oxygen, hydrogen, and nitrous gas. In 1784, Cavendish decomposed water. In 1775, Lavoisier analyzed atmospheric air, combustion, etc. In 1784, the New Nomenclature appeared, and conferred conventional language. The first object is the Nomenclature: Sulphur, by combining with oxygen, produces an acid. But this acid is in two states of saturation, having different properties. It is then requisite to follow all the saline compounds of these two acids, and to attend to sulphur in its other direct combinations, with earths, alkalies, and metals. Five terminations distinguish these five states of the same principle.

1. Sulphur ic acid denotes sulphur in the utmost degree of saturation with oxygen.

2. Sulphur ous acid denotes sulphur united with a smaller proportion of oxygen.

3. Sulph ate is the generic name of all the salts formed by the sulphuric acid.

4. Sulph ite is the name of the salts formed by the sulphurous acid.

5. Sulphur et is the name of all the combinations of sulphur not acidulous.

Combined with oxygen, Carbon is Carbonic acid. The same in gas, is carbonic acid gas. Oxydized, and forming salts with bases of earth, alkali, or metal, it is called carbonate of lime or potash, or iron. Combined without oxygen, it becomes with iron carbur et of iron, etc.