SPECTACLE SECRETS.CHAPTER I.
SPECTACLE SECRETS.
“Science should be stripped of every thing that tends to clothe it in a strange and repulsive garb, and especially every thing that, to keep up an appearance of superiority in its professors over the rest of mankind, assumes an unnecessary guise of profundity and obscurity, should be sacrificed without mercy.”—Sir I. F. W. Herschel.
“Science should be stripped of every thing that tends to clothe it in a strange and repulsive garb, and especially every thing that, to keep up an appearance of superiority in its professors over the rest of mankind, assumes an unnecessary guise of profundity and obscurity, should be sacrificed without mercy.”—Sir I. F. W. Herschel.
Spectaclesand side-saddles, we are quaintly informed, became common in England in the reign of Richard the Second. The ancients, however, knew the power of burning-glasses, and one cunning rogue, we are told, discovered a new way to pay old debts, by means of a round stone or glass used in lighting of fires, with which he melted the bond, written, as usual in those days, on wax. Their burning glasses were spheres, either solid or full of water, their foci were consequently very short and confused. A long interval occurred before spectacles were constructed, and three hundred years elapsed between the invention of spectacles and telescopes.
Our eyes should have our nicest and most tendercare, since it is by them we are familiarized with objects of the most exquisite interest and beauty, abounding on the earth we inhabit, and in the starry firmament above us:—
“My soul, while Nature’s beauties feast mine eyes,To Nature’s God contemplative shall rise.”—Dodsley.
“My soul, while Nature’s beauties feast mine eyes,To Nature’s God contemplative shall rise.”—Dodsley.
“My soul, while Nature’s beauties feast mine eyes,To Nature’s God contemplative shall rise.”—Dodsley.
“My soul, while Nature’s beauties feast mine eyes,
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 itmaysometimes 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 suchcases 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 conclusiveand 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 withone of our most sensitive and easily deranged organs. The human eye is composed of a series of humours and membranes: the outer coating, called thesclerotica(a), seePlate, 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. Thecornea(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 thechoroides(c); it has no muscular motion except at its extremities, near the front of the eye. Theiris(d) is next apparent; it attaches itself to the sclerotica by a cellular substance called theciliary 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 thepupil(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 thepigmentum nigrum. The last coating of the eye is theretina(g), a delicate and most important membrane in the construction of this noble instrument; it is an expansion of theoptic 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., theaqueous(i), thechrystalline(k), and thevitreous(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, fillingnearly 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.
Fig.2.represents the eye at the time when spectacles are required, the cornea, or the chrystalline, or both, having lost a part of their natural convexity, consequent upon age or constitutional weakness. An object placed at the same distance from the eye as in the perfect eye, (Fig.1), has the focus carried beyond the retina. A convex lens applied to the eye compensates for this loss of capacity, and, converging the rays, corrects the focal distance, and the image is now imprinted naturally on the retina. The reverse of this takes place in the case of the short-sighted; the humours beingmoreconvex than in the perfect eye, the rays converge in a focusbeforethey reach the retina. A concave lens carries the focus further on, and, by its aid, an object will be depicted perfectly on the retina.
No. 4 represents a plano convex lens—5, a double convex—6, a plano concave—7, a double concave—8, a periscopic or meniscus lens.
What grandeur and sublimity of contrivance is here blended with simplicity of action and power of expression! How indispensable to a full appreciation of the bounties of nature and the beauties of art by which we are surrounded! To be deficient of this heavenly gift is truly to have “wisdom at one entrance quite shut out.”
Surely every consideration should influence us to treat this invaluable faculty with judicious care, instead of allowing it to be tortured and trifled with by the ignorant and unprincipled.
Having surveyed the general construction, and glanced at the inimitable mechanism of those windows of the soul, we shall be better prepared to understand the reasoning, and to comprehend the principles upon which the science of optics is based. Those of my readers who have leisure to pursue this subject, will find new light, and more convincing illustrations attend their enquiry at every step. It is a subject abounding in beauty and interest, introducing us to new regions of sublimity and grandeur, where the contemplative mind will assuredly find “ample scope and verge enough” to gratify its most exalted anticipations. We have seen the admirable, yet at the same time delicate contrivances by which the functions of the eyes are performed. It cannot fail to have occurred to us, that a machine so beautiful and complete is liable to derangement and improper treatment by the wayward and the ignorant. If it is desirable that a person possessed of a well-constructed watch should understand its general action, and know what treatment it should have to keep it in sound and underanged order, still more essential is it that every individual should possess a clear and familiar knowledge of the nature of vision, and understand the requirements of the eyes. I cannot forbear indulging a sanguine hope that the circulation of this little manual will open the eyes of its readers to the simple facts of the case, and animate them to think and judge for themselves, instead of giving a ready ear to the marvellous and ridiculous tales, which, though, like the sailor’s tough yarn, so often told that the cheat believes them himself, are nevertheless utterly devoid of truth.
FOOTNOTES:[1]In the month of August, 1838, the solicitor to the Duke of Wellington waited upon Sir Frederick Roe, at Bow-street, in reference to the use which had been made of his grace’s name by “The London Equitable Loan Company.” A gentleman, who was desirous of purchasing shares in the company, seeing the Duke of Wellington mentioned as patron, and that the account of the company was kept with the Bank of England, wrote to the Duke to ascertain if it were true that he was connected with the concern? The duke never had consented to become a patron, but, on the contrary, when asked to do so, answered that he was so situated that he could not comply with their request. On receiving the communication the duke wrote to Sir F. Roe, to see what could be done to guard the public against any transaction which might be entered into in consequence of the use made of his name; and in answer to a letter written by him to the Bank of England, he was informed “that no such company was known there, nor had they any account of the London Equitable Loan Company.” The publicity given to this manœuvre has no doubt saved many a family from enthralment and destitution.
[1]In the month of August, 1838, the solicitor to the Duke of Wellington waited upon Sir Frederick Roe, at Bow-street, in reference to the use which had been made of his grace’s name by “The London Equitable Loan Company.” A gentleman, who was desirous of purchasing shares in the company, seeing the Duke of Wellington mentioned as patron, and that the account of the company was kept with the Bank of England, wrote to the Duke to ascertain if it were true that he was connected with the concern? The duke never had consented to become a patron, but, on the contrary, when asked to do so, answered that he was so situated that he could not comply with their request. On receiving the communication the duke wrote to Sir F. Roe, to see what could be done to guard the public against any transaction which might be entered into in consequence of the use made of his name; and in answer to a letter written by him to the Bank of England, he was informed “that no such company was known there, nor had they any account of the London Equitable Loan Company.” The publicity given to this manœuvre has no doubt saved many a family from enthralment and destitution.
[1]In the month of August, 1838, the solicitor to the Duke of Wellington waited upon Sir Frederick Roe, at Bow-street, in reference to the use which had been made of his grace’s name by “The London Equitable Loan Company.” A gentleman, who was desirous of purchasing shares in the company, seeing the Duke of Wellington mentioned as patron, and that the account of the company was kept with the Bank of England, wrote to the Duke to ascertain if it were true that he was connected with the concern? The duke never had consented to become a patron, but, on the contrary, when asked to do so, answered that he was so situated that he could not comply with their request. On receiving the communication the duke wrote to Sir F. Roe, to see what could be done to guard the public against any transaction which might be entered into in consequence of the use made of his name; and in answer to a letter written by him to the Bank of England, he was informed “that no such company was known there, nor had they any account of the London Equitable Loan Company.” The publicity given to this manœuvre has no doubt saved many a family from enthralment and destitution.