The Senses and the Mind

by Anonymous

2. Its Electrical Condition.—With the electrical changes in the state of the atmosphere are connected various transitions from heat to cold, dew, rain, hail, snow, clouds, winds, thunder-storms, auroræ boreales, haloes, parhelia, etc. In this point of consideration the atmosphere bears upon organic life. The solid globe itself may be regarded as a vast electrical or galvanic apparatus, and all the vital functions of animal bodies involve electric or galvanic phenomena. Magnetism appears to be essentially identical with electricity; both are most intimately connected with light and heat; and not only electric sparks, but all the phenomena of electricity, can be obtained from a common magnet. It is not here our purpose to enter into a philosophical treatise on electricity and galvanism; a little consideration, however, will lead us to infer that the general diffusion of this subtle electric fluid, if the term fluid be at all applicable, is essential to the maintenance of organic life, and that electrical changes are perpetually taking place in organic bodies. This fluid is derived from the earth, or its circumambient atmosphere, and its currents obey definite laws, which have been elucidated by the experiments of some of the most profound philosophers of modern times.

After what we have briefly said respecting the electric condition of our globe, and the electrical phenomena which are involved in the processes of the vital functions, to say nothing of electro-magnetism, it must surely be apparent, that even as the air is in itself necessary to our existence, so the diffusion of that subtle matter, now quick, now slowly acting, now energetic, and now darting from the clouds to the solid earth a vivid flash, creating a momentary light in darkness—is equally essential; this is a point which, by the world at large, is but slightly taken into consideration. Remove this subtle element from the earth, and what would be the result? Perhaps the globe would deviate from her course; perhaps an alteration in her polar axis would take place. Perhaps—but why enter into such speculations? This is certain—animal and vegetable life, as at present constituted, could not exist: but all is ordered aright; the organization of matter, and the senses of living beings, are involved in the presence of an element, variable, it may be, in its phases, but mighty in its effects. Here animals and plants play their part transversely, for each other's benefit; animals produce electricity, by means of the vital operations of their organization, and this produce, given to the earth and air, is abstracted by plants. They antagonize each other, and the result is harmony.

3. Its Illumination.—Light is evolved by and during the combustion of various bodies, as wood, coal, tallow, and spirits, or alcoholic fluids; it is the result of electricity—that is, of the electric spark or flash; it is evolved during many chemical experiments, and by the attrition of two quartz pebbles. The percussion of flint and steel produces luminous sparks; these sparks consisting, as the experiments of Mr. R. Hook have proved, of minute ignited globules of iron, struck off at the moment of percussion. These, and many other sources whence light proceeds, need not here be detailed; our object is with that general light, the light of day, which results from the influence of the solar rays. For the reception of pictures on the retina by means of the rays of light reflected from all things within the scope of vision, the eyes of animals are especially constructed. To some animals a dim twilight suffices, so far as regards their personal maintenance and their enjoyment of life; to a few the little light, which even in the darkest night is not absent, is all that is required for their ordained habits and economy. In such instances, the retina is exquisitely susceptible, and the iris dilates to admit the entrance of every feeble ray reflected from the objects either of their search or avoidance. Often have we seen the owl, when twilight has melted into darkness, skimming over the fields, along the lane, and around the barn, quartering the ground in search of mice or moles, which, had they been at our feet, would to our eyes have been invisible. On the other hand, they would have been nearly, if not quite invisible to the owl in the full glare of sunshine. Yet, be it understood, light is as essential to the night-bird as to men, or the giraffe of the glowing wilds of Africa. We know not what total darkness is, unless perhaps we be walled up in a deep dungeon underground, to which light is utterly denied access; such living tombs have been contrived by the diabolical minds of tyrants, pagan and papistical. In the darkest night, even our eyes dimly discern the "form of things obscure"—things which, to a nocturnal animal, would be boldly conspicuous.

Light is a stimulus both to the animal and vegetable worlds. It is when daylight breaks that "man goeth forth unto his work and to his labour until the evening;" it is when light breaks that the feathered songsters of the grove join in one chorus of—why may we not say so?—instinct-urged thanksgiving. O man, gifted with reason! O man, the heir of immortality! utter, then, thy song of praise, of gratitude, that the light of another day is bestowed upon thee: and then be diligent in all that God has called upon thee to perform, seeing that "the night cometh, when no man can work."

Light is a stimulus, more or less grateful to every living creature. Reader, have you ever wandered along the sea-shore, and explored the masses of rock left uncovered when the tide is fully out; there, adhering to the surface of the stone, in little ponds, mimic bays, may be seen scores of sea-anemonies (actinia.) If the sky be bright, there will they be, with their painted tentacles all expanded, animal flowerets feeling the influence of light; but let the sky change, let clouds obscure the day, and they retract their tentacles and shrink into repose. These animals have no eyes, but yet they are sentient of light. We mention these sea-anemonies merely by way of example; other eyeless, and we may say, apparently nerveless creatures evidently enjoy the influence of light, as the hydra, the medusa, and the polyps of corals.

If light waken up some animals from their repose—if it rouse the cock, and bid him sound his "clarion shrill," it warns others to retire to their obscure dormitory, and slumber till twilight recalls them into activity. The moth now flits abroad, and the bat and the fern-owl are on the wing, giving chase to their insect prey. The hedgehog is all alert, searching for slugs, worms, and various creeping things, which revel in the dews of sunset. It is then, too, that the fierce prowlers of the forest issue from their lair, eager for blood; but when "the sun ariseth, they gather themselves together, and lay them down in their dens."

Light is not only a stimulus to animals, in the sense above noticed; it appears to be essential to health and vigour. Of this we are the less aware, because, under ordinary circumstances, we are always subject to its influence. Men have been confined for years in dark dungeons, and have reappeared upon the stage of life, pallid, meagre, weak, and emaciated beings, like breathing corpses; confinement, bad food, ill ventilation, and mental agony, had no doubt done their work; but want of light also had part in the sad devastation of the animal frame. Look, for example, at those parts of our bodies which are usually clothed, and compare the colour of the skin with that of the hands and face; strip the arm bare—the skin is acted upon by atmospheric air, but yet how much whiter than that of the hand, delicate as that hand may be. It may be said that heat, that is, solar heat, produces the difference. Partly so, no doubt, but not altogether. The face and hands of the Esquimaux are darker than his chest; moreover, suppose a severe and extensive cut happens, and that the wound thus inflicted is bound up for weeks by adhesive plaster, what do we see on removal of the straps and bandages?—a singular whiteness of the skin, the result, as it appears to us, of the exclusion of light from the covered portion. Plants, as all must have noticed, have their leaves and flowers drawn towards the light, and become pallid when kept in dark places. Thus, for example, some flowers open only when the sky is clear, as the little pimpernel, the index of fair weather; others, as the sunflower, turn to the sun in his course from east to west; the eyes, or germinating stalk of the potato, though they shoot vigorously in the dark, are blanched; so are the covered leaves of endive, and the covered stalks of celery and sea-kale. Light is a chemical agent; light, as the apothecary well knows, greatly impairs the activity of the dried and powdered leaves of foxglove, and blanches castor oil. Light, therefore, is found to effect both chemical combination and chemical decomposition.

In nothing, perhaps, is the chemical agency of light more clearly shown than in the photogenic drawings, which are the fac-simile representations of objects delineated by the action of light on a thin sensitive layer of ioduret of silver. The following is the mode of preparing the plates for the reception of photogenic drawings, given in the Penny Cyclopædia:—These drawings "are produced on plates of copper, coated over with silver, which are found to answer better than such as are entirely of the last-mentioned metal. After being washed with a solution of nitric acid, the plate is put into a well-closed box, where it is exposed to the action of iodine, a small quantity of the latter being placed at the bottom of the box, with a thin gauze between it and the plate. A layer of ioduret of silver is thus formed on the surface of the plate, and manifests itself by the yellow hue produced on the silver, which shows that the process of giving the plate the sensitive coating on which the action of the light delineates objects is completed. Thus prepared, the plate is placed within a camera obscura, of particular construction, and the delineation of the object is then effected in a very short space of time; but has to be afterwards brought out and rendered distinct by another operation, namely, submitting the plate to the action of vapour of mercury. Even then the process is not completed, for the plate has to be plunged into a solution of hyposulphate of soda, and afterwards washed in distilled water, which being done, the impression is fixed, and the plate may be exposed to light with perfect safety."[4] With reflection, refraction, and polarization of light, we have here no concern; therefore, interesting as the subjects are, we must pass them by.

[4] For further details, see the Handbook of Heliography, London, 1840; and (for preparing-paper) the Visitor, 1839, p. 290.

Light radiates from the sun with almost inconceivable velocity; that is, at the rate of nearly 200,000 miles in a second. Hence it is about eight minutes in traversing the intermediate space between our globe and its starting point or origin. But here comes a question not easily answerable. What is light? Is it matter? It is imponderable—can we conceive of matter without weight? Again, whence does it derive its velocity? The term radiation from the sun is convenient; but, then, what is radiation? Is there light, (and is there heat,) above the limits of our atmosphere? We cannot tell what the nature of the mysterious emanation of light and heat from the sun is, nor whether there are such phenomena as light and heat in empty space. Again, by what process is this enormous manufactory of solar emanation kept up? We may here lose ourselves in vague conjectures: He alone knows who said, "Let there be light: and there was light."