To Nature’s God contemplative shall rise.”—Dodsley.
The faculty of sight should be estimated and regarded by us with more than ordinary care, when we reflect that it is the medium through which the most exalted and gratifying impressions are received; and our watchful regard to its healthful preservation and agreeable exercise is the more required from the consideration, that while to its admirable organization and delicate sense of perception we stand so much indebted, those very qualities render it extremely sensitive to injudicious treatment.
It would be a wholesome, fair, and proper regulation, to restrain all from practising as opticians but those practically conversant with the production and application of lenses for the purpose of aiding the exercise of sight. It is considered indispensable for the surgeon and medical practitioner to prepare for his profession by a course of study, reading, and practical operations, and to be subjected to an ordeal where his capabilities are examined and tested. Such an arrangement, though it may sometimes be abused, guarantees to us practitioners who understand their duties; and thus are the many “ills which human flesh is heir to” alleviated and subdued, while those unfortunates who are practised upon by the empiric and miracle-monger, have their calamities aggravated, and their sufferings increased.
It is a question often mooted, how far it is the duty of a just and equal government to interfere in such cases for the protection of its subjects: this, however, is evident, that whatever restrictive laws are framed, if they are attempted to be enforced while a want of information prevails upon the subject, the very people for whose benefit and protection they are introduced, will, likely enough, view them with distrust and suspicion, and, until the imposition has been unmasked, will look upon those who have assumed characters not their own, as persecuted individuals, entitled to their sympathy rather than their detestation. It is by diffusing information, and clearing away obscurity, that we shall erect the best safeguard against delusion. Those who are ignorant are consequently credulous, superstitious, and undefended against the tricks and subtleties of the artful and designing.
If a book is published, our opinion is almost insensibly influenced by what the reviewers say of it. If a new association, a company, or enterprise of any kind is projected, we look to the list of directors, committee, and patrons. Our education and universal custom induces us to pay deference to those whom we suppose to be possessed of superior information, to be men of character and reputation, and entitled, from their position in society, to be regarded with respect.
These legitimate feelings have been so poisoned and tampered with by those who have designedly entered into a conspiracy to hoodwink the people, and share the plunder; and again by the hardly less criminal apathy of others, who, without dividing the spoil, have suffered the trickery to pass unexposed; that professional and literary men cannot but perceive distrust and want of confidence in their decisions, now becoming general among the reflecting and intelligent classes of society, who see that they have been trifled with, and treated as credulous dupes, and that they really have no guarantee for the merits of a production, the purity of a proposal, or the honesty or propriety of any measure to which distinguished names and lofty patronage are appended. The exposé of the practices of the railway, mining, and other bubble schemes illustrates this truth; and the secrets elicited during the discussion on Mr. Serjeant Talfourd’s Copyright Bill, clearly demonstrate how infamously the confidence of “a generous public” has been abused.[1]
The great and benevolent men who existed before us, and devoted their time and contemplations to the interesting science of optics, have fully and clearly demonstrated the laws which regulate the action of light, the cause and effect of luminous phenomena, and the principles upon which vision depends. We have the conclusive and unvarying results of their numberless experiments, performed under every modification of circumstances, to guide us in establishing principles and rules of action, which the studious and practical opticians of our own times have tested, and, ascertaining them to be free from error, now adopt and act upon them.
The captious and consequential may complain of this admission, as tending to detract from the importance with which they might otherwise be regarded; but the optician, who deserves that name, is not anxious to array himself in borrowed plumage, nor to appropriate as his own that which rightfully belongs to others. Granted that we act upon settled and incontrovertible philosophical principles, is it not infinitely more gratifying to have the assurance of a correct result, than to be for ever experimentalizing without arriving at a satisfactory conclusion? The skilful surgeon and the talented engineer are guided in their operations by certain fixed and universal laws, yet no one will dispute that to perform the duties of either of those professions requires much application, skill, and expertness. Precisely so with the optician of the present day. He has fixed, universal, and certain data for his operations; and it is upon his intimate knowledge of these, and the careful and judicious application of them, that his success depends.
When the healthy powers of vision begin to fail, we feel a tender and anxious concern to perpetuate the enjoyment we find to be so intimately dependent upon the uninterrupted exercise of sight, and are instinctively led to seek for a remedy. Much mischief will be avoided, and misapprehension removed, if we consider that in applying artificial aid to the eye, we have to do with one of our most sensitive and easily deranged organs. The human eye is composed of a series of humours and membranes: the outer coating, called the sclerotica (a), see Plate, Fig. [1], is exceedingly strong, and the muscles which move the eye are attached to it; the white of the eye is a portion of this coating. The cornea (b) arches out or projects from the eye-ball; it is transparent, and of a circular form. The next coating to the sclerotica is called the choroides (c); it has no muscular motion except at its extremities, near the front of the eye. The iris (d) is next apparent; it attaches itself to the sclerotica by a cellular substance called the ciliary circle (e). According to the colour of the iris the eye is termed black, blue, hazel, &c. It is composed of two sets of muscular fibres, the one tending, like radii, towards a centre, the other forming a number of circles concentric with the same centre. The aperture in the iris is called the pupil (f); it is always round, but varies in diameter as the radial or the circular fibres of the iris are contracted or expanded, according to the quantity and quality of light it is required to admit, acting like a watchful centinel to regulate the amount of rays requisite to transmit a perfect and well-defined image of objects onwards to the brain, which, without its agency, would appear one undistinguishable mass of confusion. The chamber of the eye is darkened by the posterior surface of the choroid membrane having a lining of dark-coloured mucus, called the pigmentum nigrum. The last coating of the eye is the retina (g), a delicate and most important membrane in the construction of this noble instrument; it is an expansion of the optic nerve (h), directly emanating from the brain; and is spread like a net of exquisite delicacy all over the surface of the choroides, terminating at the ciliary ligament. It receives the images of objects by means of the rays of light that enter at the pupil; it is transparent, but appears black on account of the dark pigmentum behind it. The optic nerve passes through a small aperture in the “architectural dome” containing the eye, and it conveys the impressions made on the retina into the depository of the brain, where the “very form and spirit of the scene is now conceived.” It is situated a little on one side of the centre of the eye, inclining towards the nose.
To describe more minutely the various fibres, humours, and ciliary processes of the eye, or to enter more fully into its anatomical arrangement, would be incompatible with the design of this publication, which is intended for the “general reader,” and therefore so simplified as that it is hoped he cannot fail to understand. The three transparent humours enclosed by the coats of the eye, viz., the aqueous (i), the chrystalline (k), and the vitreous (l), are, however, too important to be passed over without some notice. The aqueous (i) humour it is which gives a protuberant figure to the cornea (b); it has a refractive power, similar to that of water, which it also resembles in appearance. The chrystalline (k) humour is more transparent than the purest chrystal; its form is that of a double convex lens, which it also resembles in its use, as it converges the rays which pass through it, from every visible object to its focus on the retina. It is suspended in a fine transparent sheathing. The shape or convexity of this natural lens alters occasionally, and shifts a little backwards or forwards in the eye, so as to adapt its focal distance from the retina to the different distances of objects. The vitreous humour is situated at the back of the chrystalline, filling nearly three-fourths of the globe of the eye; it is surrounded by a thin capsule, which sends off a number of membranous processes into the vitreous substance, where they form cells, which, communicating with each other, give a high degree of firmness and tenacity to the whole.