GIFT or George H. Kahn, HlUybirtV uBHAKY QEO. H. KAHN s^C*^ THE EYE! 41 ITS DISEASES AND THEIR CURE; COMPRISING A FAMILIAR DESCRIPTION OP THE ANATOMY AND PHYSIOLOGY, Oy THE ORGAN OF VISION: RULES FOR THB PRESERVATION, IMPROVEMENT, AND RESTORATION 01^ SIGHTj WITH REMARKS ON OPTICS, ON NEAR SIGHT AND AGED SIGHT; AND THE USE AND ABUSE OF SPECTACLES, WITH DIRECTIONS FOR THEIR SELECTION. BY JAMES W. POWELL, M.D., CflKB OP THE COLLEGE OF SURGEONS, OCULIST, AURIST ; AUTHOR OF A TEEATMB ON THE ASIATIC CHOLERA, &C., &C. * aijirb (BWion. NEW YORK: PUBLISHED BY THE AUTHOR, AT 261 BROADWAT, AND SOLD BY ALL BOOKSELLERS. 1849. OPTOMETRY Entered according to the Act of Congress, in tlie year 1847, by JAMES W. POV/ELL, M.D., the Clerk's Office of the Dii?tr!ct Court of the Southern District of New York V- S. Bank Note Reporter Printing Office. Da. POWELL'S Hours of Attendance, at his Residence and Officqa, 261 Bhoadway, (entrance 1-^ Warbex-stbeet,) Art from ISine io I'hur. My Dear Doctor, The kindness which you evinced towards me during my studies under your superintendance, from 1828 to 1833. prompts me at this distance of time and place, respectfully to dedicate to you this Treatise, in which I have attempted to popularize the science of Vision — a department of knowledge, give me leave to say, on which your genius has already shed such lustre. I trust that this little work may not be found wanting-in usefulness to those for whose benefit it is intended. I will be ♦' Content, if hence th' unleam'd their wants may view, The learn'd reflect on what before they knew." Ever gratefully, Your Friend and Pupil, J. W. POWELL, Dr. JACOB, Professor of the Diseases of the Eye and Ear, Lecturer on Anatomy and Physiology, Royal College of Surgeons, Dublin. Ntio York, May 15, 1S47. CONTENTS. Dedication, .-.----vii Preface vo First Edition, -xv Preface to Second Edition, -.- xvii 7nlroduction, -- idx Optics — Nature of Light — Its properties — Moon and Stars — Rays of Light — Refraction — Convergence and Divergence of Rays— Lenses — Burning / Glass — Archimedes — BufTon — Parker — Microscope — Magic Lantern— Light-houses— Mirage — M. Monge — French Army — Dr. Vincent— Ramsgate — Dover — Capt. Scoresby — Greenland Sea— Fata Morgana— Straits of Messina— Minasi — City of Reggio — Reflection of Light — Mirrors — Specula — Kaleidoscope — Compound Nature and Divisibility of Light— Sir Isaac Newton— Mother of Pearl— Barton— Iris Ornaments— The Rainbow — Brewster — Heating Power — Colors how formed — Mag- netic Property of Rays— Farraday — Formation of Images — Camera Obscura — Daguerreotype — Mr. M. B. Brady — Telescope — Convex and Concave Lenses - 21 Anatomy of the Eye— Form— Bony Socket— Coats — Sclerotic- Choroid- Retina — Cornea — Humours — Aqueous — Vitreous — Crystalline— White of the Eye— Fishes — Birds — Pigmentum Nignim — Albino — Animals of Prey — Ciliary processes — Jacob's Membrane — Chambers of the Eye- Membrane of the Aqueous Humor— Iris— Pupil— Byron— Eyelids— Mel bomian Glands — Lachrymal Passages and Sac — Oaruncula Lacrymalis — Eye-lashes — Orbicularis Palpebrarum — Levator Palpebrae — Eye-brow — Lacrymal Gland— Tears— Conjunctiva— Muscles of the Eye— Straight — Oblique — Dr. Jacob — Pathetic Muscle — Nerves— Optic Nerves -Fora- men Opticum — Fifth Pair of Nerves — Sneezing — Schneiderian Mem- brane— Blood-vessels— Ciliary Arteries - - - - 38 Physiology of the Eye — Vision — Inverted Image — Eye of an Ox— Impression retained — Circle of Light — Painted Wheel — Thaumatrope — Ocular Spec- trum — Harmony of Colors — Pictures — Supernatural Appearances — In- sensibility to certain Colors — Anecdotes — Edinburgh Tailor— Naval Officer— Priestley— The Artist— Green Moustache— Blue Cheeks— Appa- rent Magnitude — Landscape and Architectural Painting — Sense of Touch— Blind Persons— Reverberation— Singleness of Vision— Delirium —Intoxication — Adjusting Power of the Eye, - - - - 47 CONTENTS. Diseases of the Eye — Ophthalmia — Chronic — Egyptian — Inrantile— Symp- toms — Treatment — Cases — Granular Lids — Treatment — Cases — Ptery- gium — Inflammation of Sclerotic, Cornea, Ulcers — Cases — Nebula?— Opacities — Specks — Cases — Staphyloma — Iritis — Symptoms — Cases — Closed Pupil — Cataract — Catopric experiment — Purkinje of Breslau — Amaurosis- Symptoms— Cases— Fungus Hocmatodes — Cancer - 53 Affections of the Eye-lids — Psorophthalmia — Causes — Symptoms — Treat- ment— Trichiasis — Entropium — Ectropinm — Hordeolum or Stye — Na3vi Materni — Ptosis- -Fistula Lachrymalis — Treatment - - 73 Strabismus or Squinting — Causes — DiefTenbach — Chinese — Descartes- Injuries and Accidents — Dust — Sand--Insects — Railroad Sparks— Emery — Steel-r-Iron Filings— Chips of Wood— Stone— Detonating Caps— Lime — Fused Metals — Scalding Water— Concentrated Acids — Method of Treatment— Cases— Black Eye—" Rowdy's Coat of Arms"— Musquito Bites— Other Insects - - - - - - -80 Artificial Eyes — Beautiful Substitute— Enamel — Gems of Art— Colors of Iris— Brilliancy of Cornea — Difficulty of Detection — Correspondence of Motion— Personal Appearance— Great Advantage — Method of Introduc- tion— Removal — Precautions — Culpable Ignorance — Horrible Operation — Maiame Pluyette — Amusing Trial - - - - - 83 Advice to Patients — Pure Medicines — Personal preparation of them— New- ton— The two Herschells — Farraday— Earl of Rosse— Medical Pro- fession—False Standard of Dignity— Hap-hazard— Doubtful Stock — ' Careless Apprentice — Dangers of Delay — Random Experiments — Spe- cifics— Eye- waters — Ealsams---Experienced Oculist— Public Institutions — Erroneous Practice— Bleeding— Blistering- •Oupping--A PUl at Night — Salts in the Morning — Co-operation of Pati':?nts, - - - 87 Preservation of Vision— Improvement — Prevention of Disease — Blindness — Milton — Influence of the Mind— General Health — Constitutional Causes—" Mens sana incorpore sano" — Temperance— Alkohol — Liebeg — Double Vision— Red and Bleared Eyes— Regular Hours— Old Adage —Journal of Elizabeth Woodvi'le, (iueen to Edward IV. — Clothing— W^ooUcn and Silken Goods— Linen — Cotton — Washing and Bleaching —Frequent Changes — Damp Feet— Tight Dress— Corsets— Ladies' Bonnets — Colors — Flowers— Ribbons — Parasols — Sun-shades— Veils —Fans - - - - > - - - - 91 Tho Bath — Temperature— Test of its '••«;nefit— Insensible Perspiration — Pores, enormous length of, 28 miles— Scarf Skin— Unctuous and Saline Products of Skin— The Skin a Respiratory Apparatus— Miasma— In- fectious Matter — The Shower Bath— Training necessary— Locke's Patent Baths— Plunge Bath— Jet or Douche Bath— SELF-ACTING EYE-FOUNTAIN, I'.s great advantages, immediate relief, jDre»>C:i-vative CONTENTS. power — Vapor and Medicated Baths— Cheap substitute — Temperatni» —Temperate— Tepid — Warm — Hot — Soap — Coarse Towel— Friction Horse Hair Gloves — Dinnelbrd's - - Cummming, Dodge and Co. — Bathing Room— Wet Sponge— Salt Water Bath— Tonic Effects— Time of taking bath- Art of Swimming — Philosophical Facts — Caution — Ap- pearance of depth of water deceptive — Dr. Rabineau — Floating Baths — Hot Salt Water Baths— Astor House - - - - - 98 Exercise — Sedentary Habits — Walking — Exercise without soul — Mind amused — Eye delighted — Country Air — Clear Sky — Green Fields — Cheerful Friend — Roman Poet— French Traveller— Exercise on Horse- back—Cricket — Quoits— Leaping — Running — Gymnastics — Dumb Bells — Skipping Rope — Shuttle-cock— Graces — Kalisthenics — Mode- ration — Regularity — Appropriate Time, - ... 109 Diet — Wholesome and sufficient Food- Animal— Vegetable — Soups— Cooking — Boiled — Roasted — Broiled — Culinary Operations — Requisite skill — Liebeg's letter to Professor Silliman on Cooking — White and young Meats — Beef— Mutton — Aquatic Birds — Baking — Frying — Feelings often the best guide — Idiosyncrasy — Case of a Lady — Generous Diet — Boiled Leg of Mutton — Roast Beef— Broiled Mutton-chop— Back of a Rabbit — Fowl — Sweet-bread — Tripe — White Fish — Oysters — Eggs — Potatoes — Turnips — Asparagus — Tomato-es — Fruit — Pure Croton — W^ine — Ale— Porter — Brandy— Tea — Coffee — Goat's Milk — Asses Milk — Butter Milk— Rain— Spring— Pump and River Water — Animalcules — Vegetable Parasites — Oxyhydrogen Microscope — Jennison's Dia- phragm Filter— Indigestible Food— Salt and Smoked Meats — Salt Fish — Butter — Fatty Substances — Hot Bread---Rich Cakes — Pastry — Lob- sters—Regular Hours for Meals— Proper Intervals— Rest— Abernethey — Gourmand's Motto— Digestive System— Habit of taking Medicine — Mild Apperients — Regularity, - - - - - - HI Tobacco— Habit of Smoking — Dr. Laycock — Quantity consumed — Effects — Mucous Membrane — Stomach — Lungs — Heart — Brain — Nervous Sys- tem — Eyes — Teeth — Sallowness — Consumption — Dr. Wright, - 116 Education — Physical— Mental — Reason of Short-sightedness — Tasks — Over- application— Youth the period of Action — Guide for Physical Education, 118 Houses, Offices and Manufactories — Location — Marshes — Rooms — Modem Windows — Reflected Light — Merchants — Princely Palaces — Back OiBces — Sleeping Apartments — Manufactories — Ventilation— Dirty Streets — Regularity of Light— Wmdow Shades— Walls — Furniture-- Gilding — Position of Bed — Perspective — Wisdom of Providence — Cradle to the Grave — Little "Deary" — Sudden Transition — French Bastille — Robespierre — " Man's Inhumanity to Man " — Dionysius the Tyrant — The Carthagenians — Regulus — Roman Eagles— Battle Field, - 120 Artificial Light— Day-light — Contrast— Increased Heat— Great Desideratum — Good Lamp— Dr. Ure— Mechanical or Carcel Lamp, Objections to — Parker's Hot Oil Lamp— Frenrh Annular Lamps— Cost of Illuminak CONTENTS. tion — Candles — Protection — Shades — Ultra Marine — Refreshing — Glass Chimneys— Ground Glass Shades-Cut of Glass Globe — Ammoniated Copper — Carbonic Acid Gas — Headaches — Eyes — Compositors — Morn- ing Papers — Ventilation — Foul Air — Lyceums — Lecture-rooms — Public Buildings— Arrangement of Lights^ - - - - - 124 GENERAL OBSERVATIONS. Rubbing the Eyes — Bathing the Eyes — Douche — Rose-water — Eau de Cologne — Brilliant reflected light — Unlettered Savage — Yeux a la neige Sandy Deserts — Thompson — Xenophon- Army of Cyrus— Dust--- Smoke— High Wind— Taxing the eyes— Bad Print— Newspapers— Ele- vated Desk — Golden Rule — Cold Feet— Young Persons — Selection of Occupation — Book-keepers — Engravers --- Watch-makers — Tailors — Shoemakers — Sempstresses— Caution — Amaurosis— Milton — Advice — Wet Sponge— Cool Air— Electro-Magnetic Battery— Silk Shades— Cele- brated Comedian — Influence of the Mind — Depressing Passions — Exces- sive Sorrow — "Like Niobe — all tears" — Serenity — Agreeable Society — Innocent Amusements, -----._ 129 Near Sight and Far Sight — Weakness of Sight — Day-Blindness — Night- Blindness — Cuba, - - - - - - -135 Short-Sightedness — Myopia — Perfect Vision — Range — Symptoms— Causes — Conformation-Refractive Media— Adjusting Power— Focal Point— Prom- inent Eyes — Near Objects— Visual Angle— Small Objects— Weak Light — Bright Light — Contraction of Pupil — Habit of Closing the Eye-lids, - 136 Far Sightedness — Presbyopia — Natural Change — Symptoms — Flattening — Adaptation to Distances — Convergence — Arcus Senilis— Distant Objects — Minute Objects — Arms Length — Candle — Density of Refractors — Extreme Old Age,. - - - - - - - - 139 The Use and Abuse of Spectacles— Light — Sight — Addison — Divine Mech- anism — Inestimable Blessing — Discovery of Spectacles— Scholar — Litte- rateur — Artist — Artisan — Simplest of Optical Instruments — Glasses — Their Action — Concave Lens — Purpose — When Requisite — Too Early Use — Age no Guide — Apprehensions — Judicious Selection — Common Error — Double Concave Glasses — Power-Precautions — Vertigo — Aged Sight — Convex Lenses — Little Piece of Glass — Triumph over Nature — Preservers — Change — Lowest Power — Magnifiers — Gradations — Opti- cians' Scale — Individual Selection — Different Focal Power of each Eye- Plate Glass — Purity — Method of Testing — Frames — Exact Centre — Pupil — Bridge — Eye-pieces — Oval — Circular— Octagon— Model of Spec- tacles — Material s — Gold — Silver — Tortoise S hell — S teel — Care- J oints — Pebbles — Periscopic — Dr. Woollaston — Cataract Glasses — Quizzing Glass— Advice— Double Hand Eye-glass— Tip of the Nose— Goggles — Colored Glasses— Neutral Tint— Professional Education— Urgency of Friends — Testimonials — Conclusion, ... - 142 PREFACE TO THE SECOND EDITION. The rapid sale of the First Edition of this Work, within three short months, is a gratifying indication of pubhc approval. The author takes this opportunity to thank his professional brethren for the kind reception they have so liberally accorded to it. To the Public he is also indebted for their favorable acceptance of it ; and to the Press for their valuable recom- mendatory notices. He has endeavoured to render it more deserving of the approbation already bestowed by a careful revision of all its parts, and by the introduction of some fifty pages of additional matter. PREFACE. Many valuable and elaborate work^ have been published on the Eye and its Diseases. These are not generally ac- cessible to the non-medical reader, nor indeed, clothed as they are in the technicalities of the profession, would they be easily understood by him. Hitherto no work of a familiar nature, embracing the subjects specified in the Title Page, has appeared. I have attempted to fill up this hiatus in the popular literature of the day, by giving, in plain and concise language, which all can understand, a description of the Human Eye, the parts of which it is composed, and those that are subservient to it, both in a state of health and when affected by disease, the rules and precautions that are necessary to prevent disease, and the simplest and best means of relief in slight affections, or on the occurrence of an accident. I have confined my observations respecting the curative means, applicable to Diseases of the Eye, to those that can be judiciously used by every person of common understanding, and have avoided alluding to the treatment of more aggravated cases because the most deplorable consequences frequently result from the use of applications, to so delicate an organ, by the inexperienced. I have incidentally touched on the science of Optics, where the connexion was necessary to illustrate the living optical XVI PREFACE. instrument under consideration ; explained the rationale of spectacles, and accounted for their necessity in advanced age, the frequency of their use in youth, the inconceivable injury that is caused by bad and unsuitable glasses, the great comfort * and advantage of those that are properly selected, together with exact rules for the accomplishment of this important object Appropriate collations are made from scientific and standard works for the elucidation of the subject, thinking that "we ought not, like the spider, to spin a flimsy web wholly from our own materials, but, like the industrious bee, visit every store and cull the most useful and the best." In the whole range of medical or philosophical subjects, not one can be named possessing more interest than the Science of Vision ; and where shall we seek for a subject on which the Public are less informed ? It is tnis want of knowledge that renders them so frequently the dupes of the ignorant empiric, who, with audacious effrontery, undertakes the treatment of diseases of an organ so pecuHarly delicate and sensitive as the Eye. But its extreme delicacy and great importance will not deter the unprincipled, whose sole object is gain, from tamper ing with and ruining the eyes of all the unfortunate victims whom they may beguile into their net. " Oh Heaven ! that there were but a mote in theirs, A grain, a dust, a gnat, a wand' ring hair, Any annoyance in that precious sense ! Then, feeling what small things are boisterous there, Their vile intent must needs seem horrible." — Shakespeare. The Diseases of the Eye, and those of other parts of the system have a geueral resemblance to each other. Tliey are PREFACE. XVU influenced b}^ the same laws wliicli govern other diseases, and their treatment is regulated by general jDrinciples. Many of the aflectlons of the eye depend upon constitutional causes; these must be understood and removed before the diseases of which they are the causes can be cured. The disorders of the Eye are indeed so numerous and di- versified, and some of the operations for their relief require so nice a combination of skill and delicacy that they should be attempted only by the experienced Oculist, and no one except the thorough Surgeon can make the complete Oculist. His science enables him to recognize the analogy between the Dis- eases of the Eye and those of other parts. His devotion and attention to this particular branch of his profession enables him to acquire that superiority and perfection, which, in any busi- ness, can be attained only by a sub-division of labor. Shall we then trifle with this precious organ, or submit it to the rash treatment of the unskilled ? How often is the Oculist considted, alas ! when too late, where by neglect or mismanage- ment the sight is irretrievably destroyed? We do not appreciate its inestimable value. We are scarce aware of the privations endured by those in w^hom it is partially or entirely annihilated, until we ourselves are sufferers : then we are ready to exclaim, in the language of the blind Bard, — " Oh, why was sight To such a tender ball as the Eye confined, So obvious and so easy to be quenched ; And not, as feeling, through all parts diffused, . That she might look at will through every pore." '* And here, I hope, it will not be deemed irrelevant, or unbe- coming, if I allude to my own professional career. XVlll PREFACE. My earlier opportunities of acquiring a practical knowledge of the profession were pursued under particularly advantageous cii'cumstances, in certainly one of the best Schools of Anatomy, Physiology and Surgery, in the world — the College of Surgeons in Dublin.* Subsequently, I engaged in extensive general practice as Physician, Surgeon, and Accoucheur. By a concurrence of circumstances I was enabled to retire from those laborious en- gagements, and devote myself to the more congenial branches that my earlier predilections were in favor of. For the extensive practice I have enjoyed in this branch of Surgery I cannot make the Public a more grateful return than by presenting them with this book. If its precepts enable them, in some degree, to understand the Eye, its imperfections, and their prevention, my wishes will be realized, my object accomplished. ♦ I have heard Dr. Mott state, in one of his Lectures, that he considered the DubUn Surgeons were unsurpassed for science and skill, and that if he himself was the subject of an aneurlsmal affection, he would immediately embark for that city and placj himself under the treatment of the Dublin Surgeons. INTRODUCTION All the org-ans appropriated to the senses by which we are connected with the material world, are necessary to our wel- fare and happiness ; but there is none so peculiarly essential as the organ of vision. This, though diminutive in point of size, is, iievertheless, the most important of them all. Nature has lavished all her skill in the formation and protection of this most beautiful and ini- mitable work. Our unbounded admiration must be excited by the contem- plation of the varied and complicated parts of which the Eye is composed ; the surprising adaptation of its mechanism to the office intended to be performed by it in the animal economy ; the celerity of its motions ; its extreme sensibility ; the wonder- ful power by which, in a moment, we can view the most distant or the nearest object, the lofty mountain, the lowly valley, the vast expanse of water, the starry canopy, the charming land- scape, with its rich and glowing colors, all imaged with unerring faithfulness on a surface scarce an inch in diameter. The Eye, as an optical instrument, is unapproachable. No art can ever form its equal. True, by artificial aid, we are fur- JX. INTRODUCTION. ther enabled to penetrate illimitable space, or unravel the mi- nute secrets of nature, but " Why has not man a Microscopic Eye 1 For this plain reason— Man is not a Fly. Say what the use, were finer optics given, T' inspect a Mite, not comprehend the Heaven ! ^ God, in the nature of each being, founds Its proper bliss, and sets its proper bounds." — Pope. The sense of vision ever affords constant and continued sources of gratification and pleasure, past and present. How vividly we remember the scenes and familiar places of our youth ; how lastingly they are depicted " In the mind's eye, Horatio." Be it our study, then, to investigate this brilhant subject, and ascertain the history of this wonderful organization. OPTICS. " Let there be light, and there was light" Hail, holy light, oflspring of heaven first-born, Or of the eternal co-eternal beam, May I express the unblamed 1 since God is light, And never but in unapproached light Dwelt from eternity, dwelt then in thee, Bright efiiuence of bright essence increate ! Or hear'st thou rather, pure ethereal stream, Whose fountain who shall tell ? Before the sun, Befoi-e the heavens thou wert, and at the voice Of God as with a mantle, didst invest, The rising world of waters dark and deep. Won from the void and formless infinite." — Milton. The science of vision and of light, and its properties ia called Optics. The nature of light is still a disputed point. Some assert that it is a fluid pervading all space, in which waves or undu- 22 OPTICS. lations are produced by the sun or luminous body, while others contend that' it consists of material particles, thrown off from the luminous body. There are, however, certain known properties appertaining to light. All bodies are termed luminous, which on being heated or rubbed, possess the property of discharging light. Non-luminous bodies have not this powder ; they only reflect the light which fails upon them. For Example : — If we light a candle in a dark room, w^e not only see the self-luminous body — the candle, but every thing else on which its rays fall. The non-luminous bodies, as the ceiling, walls, and furniture of the room, become luminous for the time, and they in their turn throw off the light again in all directions. Or, if we allow a ray of light to enter a dark room and fall on a sheet of paper, it becomes luminous, and from thence the whole apartment will be lighted. If we extinguish the candle in the former, or stop the entrance of the ray of light in the latter instance, all will be in darkness again. The moon and stars are non-luminous bodies, they but re- flect the light of the sun. Light is sent forth in all directions from every visible point of a luminous body. If we hold a sheet of paper before the sun or a candle, we perceive there is no part destitute of hght ; it is entirely covered with it. All bodies discharge light of the same color as themselves, notwithstanding the light being white which they receive from OPTICS. 23 the sun. A green leaf throws off a green color ; a red piece of cloth a red color. This is beautifully illustrated by the following well-known experiment. If a sheet of white paper is held before a rose bush, the color is as usual white, but if the paper is placed at the end of a box, enclosed on all sides, and then a pin-hole is made in the side opposite to the paper to allow the light to pass from the rose-bush, and we look through another hole at the paper, we see opposite each rose a patch of red light, and oppo- site each green leaf a patch of green light, being an inverted picture of each flower and leaf If we increase the first made aperture the colors will become less visible, if we still further increase it the paper will resume its former whiteness, m Light moves with inconceivable velocity, being at the rate of twelve millions of miles per minute. It travels from the sun to our globe in seven-and-a-half minutes ; from the north to the south pole in the 24th part of a second. Light is composed of separate parts, each independent of the other. If we close the shutter of a room and admit the light only through a small hole, and then close half of this, the rays which have passed will not be affected by their separa- tion from those which have b'een stopped. If we further close the hole, the smallest beam which we then allow to pass, is called a ray of light. Rays of light proceed in straight lines. This would have been evident during the last mentioned experiment if the room had been filled with smoke or dust. Although a ray of light proceeds in a straight line, yet if it be interrupted it can be bent. For instance, a ray of light passing through a bottle, containing fluid or a piece of glass, does not illuminate a sheet of paper placed behind those sub- 24 OPTICS. stances as it did before. This, then, is termed refraction, which will be illustrated by the accompanying diagram. C F&L A. B. O. D. represents a vessel with a hole at S. E. ig a lighted candle within a short distance of it ; then a ray of light E. S. will pass through the aperture S. and go in a straight line toahe bottom of the vessel at F. where it will form a small cncle of light. Mark the point P., now fill with water to the line h. i., then the round spot, before at P., is found at G. ; the ray has been bent at the point K., where it falls into the water, into the line K. G. If we pour in alcohol instead of the water, we will find the beam of light more bent at K. ; but if we substitute a piece of solid glass for the alcohol, we will perceive it still more bent, so as to form the line K. L. The power which thus changes the ray of light is called re- fraction, therefore we say that a ray of light falling in a slanting direction upon a liquid or solid body, through which it can pass, is refracted by them, and by different bodies, in dif- ferent degrees. ') We have all observed that when an oar is immersed in clear water it appears crooked or bent into an angle, where it enters the water. This appearance is caused by the above law of refraction. Rays of light which approach each other, as they advance, are called converging rays. OPTICS. t6 Those which recede from each other as they proceed, are termed diverging rays. The point at which the former con- verge is called its focal point. The distance of the focal point, from the refracting surface, is called the focal distance. •< Glass is the substance generally used in optical instruments, and in experiments for refracting the rays of light. The fol- lowing figures represent the different forms which are used : 1 2 3 456789 1st. A prism. This is a solid, having two plane surfaces in- clined to one another. 2d. A plane glass has two plane surfaces parallel to one another. 3d. A sphere has every point in its surface, equally distant from a common centre. I 4th. A double convex lens is bounded by two convex sphe- rical surfaces, whose centres are on opposite sides of the lens. 5th. A plano-convex lens is bounded by a plane surface on one side, and by a convex one on the other. 6th. A double concave lens is bounded by two concave spherical surfaces whose centres are on opposite sides of the lens. 7th. A plano-concave lens is bounded by a plane surface on one side and a concave one on the other. 26 OPTICS. 8th. A meniscus is bounded by a concave and a convex spherical surface, and these two surfaces meet if continued. 9th. A concavo-convex lens is bounded by a concave and. a convex surface, but these two surfaces do not meet though con- tinued. Each of these various form* has a different refractive power. The refractive power of curved surfaces are those in ost ge- nerally used in optics. The burning glass derives its power from the convex lens refracting parallel rays to a focTis. All the rays of the sun (hat fall on the surface of the glass are col- lected to a point, and intense heat is produced. The rays may also be collected by reflection from concave looking-glasses or specula. The great mathematician Archimedes, when his native city of Syracuse was besieged by the Romans, under Marcellus, it is said, burned their entire fleet by means of mirrors. The naturalist Buffon set fire to planks of wood at 150 feet distance by the same means. In more recent times the celebrated burning-glass of Parker produced so great a heat that iron plates were melted by it in three seconds, and gold exposed to its influence was almost instantly rendered fluid. It is by the property of a convex lens which refracts rays proceeding from its focus into parallel directions that light- houses throw a strong light to great distances. The microscope is simply a convex lens, in the focus of which minute objects are held ; the object is placed near the eye, its apparent magnitude is increased, and the rays flowing from each of its points are refracted into parallel rays, and the eye is thus enabled to see small things with great distinctness. The magic lantern is formed by a plano-convex lens being fixed in the tube which projects from its front. Behind and within the lantern is a lamp, the light from which passes OPTICS. # through the lens and powerfully illuminates objects painted on slips of glass which are placed before the lens in an inverted position, and these images are received on a white sheet or surface arranged for the purpose. This little machine affords to young persons a good deal of pleasure and amusement. The extraordinary phenomenon of the mirage or looming^ by which ships, coasts, and mountains seem elevated aboT« their proper level, is caused by an unusual refractive power of the atmosphere, produced by vapors and dense exhalations. M. Monge, in the Memoires sur VEgypte^ states that when the French army was marching through the sandy deserts of Lower Egypt, they saw various phenomena of unusual re- fraction to which they gave the name of mirage. When the surface of the sand was heated by the sun, the land seemed to be terminated at a certain distance by a general inundation. The villages situated on eminences appeared to be so many islands in the middle of a great lake, and under each village there was an inverted image of it. As the army approached the boundar}^ of the apparent inundation the imaginary lake withdrew and the same illusion appeared around the next village. A most interesting case of mirage w^as observed and de- scribed by Dr. Vince. From Ramsgate the tops of the turrets of Dover Castle are just visible over a hill between Ramsgate and Dover. Dr. Vince, however, on one occasion saw the whole of Dover Castle as if it had been brought over and placed on the Ramsgate side of the hill. The image of it was so strong that the hill itself was not seen through the image. Captain Scoresby, while sailing in the Greenland Sea, recog- nised his father's ship when below the horizon, from the in- verted image of it which appeared in the air. He stated that 28 OPTICS. it was so well defined he could distinguish with his telescope every sail, the general rig of the ship, and its particular cha- racter, insomuch that he confidently pronounced it to be his father's ship, the Fame, which it afterwards proved to be. In comparing notes with his father he found that their relative position at the time gave a distance from one another of nearly thirty miles, being about seventeen miles beyond the l^lprizon, and some leagues beyond the limits of direct vision. The fata morgana, which is seen in the straits of Mes- sina, and which for ages puzzled philosophers, and con- founded the vulgar, is now well known to be but another instance of this peculiar refraction. Minasi, in his glowing description of it, states that an individual standing on an emi- nence in the city of Reggio, with his back to the sun, and face to the sea, when the rising sun throws his rays at an angle of 45^^ on the sea of Reggio, can perceive upon the water numberless series of pilasters, arches and castles, well de- lineated; regular columns, lofty towers, superb palaces with balconies and windows, villages and trees, plains with herds and flocks, armies of men on foot and horseback, all passing rapidly in succession on the surface of the sea. These same objects are in particular states of the atmosphere seen in the air though less vividly, and when the air is hazy they are seen on the surface of the sea brilliantly fringed with the prismatic colors. OPTICS. REFLEXION OF LIGHT. Hitherto we have spoken only of transparent bodies. "WW have ascertained that the greater part of light is transmitted through them according to certain definite laws — a small por- tion only being reflected. But when light falls on a bright or polished body, the greater part of it is reflected or driven back, the remainder is lost within the body. The bodies which are generally used for this purpose are mirrors, or specula, commonly made of metal or glass, having their surfaces highly polished. Those of glass aie usually quick-silvered on one side, so as to reflect more light. The principle of the formation of images by mirrors is precisely the same as by lenses. When two plane mirrors are combined in a particular man- ner, and placed in a particular position relative to an object, or series of objects and the eye, they constitute the kaleidoscope. In order to give variety to the figures formed by the instrument, the objects are placed in a narrow cell between two circular pieces of glass, leaving them just room to move about while the cell is turned round by the hand. The pictures thus presented to the eye are, beyond all description, splendid and beautiful. We have as yet only described light as a simple substance ; but the white light which is derived from any luminous body is, in reality, composed of seven different kinds of light, of different colors. ^ 30 OPTICS. Sir Isaac Newton exemplified this wonderful discovery in this way — Y C"'' In a window shutter H. G., of a dark room, Newton made a hole F. one third of an inch broad, and he placed behind it a glass prism A. B. C, so that the beam of ligiit, S. F., might enter and leave the prism at equal angles. Be- fore the prism was so placed, the beam, S. F., proceeded in a straight hne to Y., where it formed a white spot ; but being now refracted by the prism, it will form on the screen, M. N., an oblong image P. T., containing seven colors, as enumerated. The oblong image is called the solar or prismatic spectrum ; and these rays which have been thus separated can be again collected by a lens, and white light reproduced. The compound nature of white light can also be demon- strated by painting the rim of a wheel with the seven pri^ matic colors, and making it revolve rapidly about its axis the colors will disappear, and white will alone be perceptible. The beautiful prismatic colors that are seen in rnother of pearl, have their origin in a particular configuration of its sur- face. Brewster, while making some interesting experiments on this subject, was surprised to find that mother of pearl had OPTICS. m the power to communicate its colors to other substances on which it was impressed, as black wax, isinglass, gum arable, balsam of tolu, fusible metal and lead, thus conclusively prov- ing that the colors are caused by the peculiar grooves or eleva- tions and depressions on the surface of the pearl. Barton very ingeniously applied the principle of the pro- duction of color, by grooved surfaces, to various substances. He contrived a machine that was capable of cutting grooves upon steel at the distance of from the 2000th to the 10,000th of an inch. He afterwards manufactured imitation jewels, buttons, and other ornamental articles of surpassing beauty and splendor. To these he gave the name of Iris ornaments from their resemblance to the varied colors of the rainbow. Nothing in nature or art can surpass their brilhant display of colors. In ordinary light these colors are scarcely distinguish- able, but in strong light, particularly that of the sun or gas, the colors shine with surprising briUiancy, and the play of tints which flit about with every luminous image are rivalled only by the matchless hue of the diamond. The Rainbow. — This beautiful phenomenon which we see when the sun is shining, and the ram falhng between us and the part of the horizon where the bow is seen, is caused by the decomposition of the v* hite light of the sun by the refraction of the drops of rain and their subsequent reflection within the drops. It consists of two bows or arches, extended across the sky, and glowing w ith all the colors of the prismatic spectrum. " Now, overhead, a rainbow bursting through The scattering clouds, shone, spanning the dark sea, Resting its bright base on the quivering blue : And all within its arch appear'd to be Clearer than that without, and its wide hue Wax'd broad and waving like a banner free, Then changed like to a bow that's bent. SZ OPTICS. It changed of course ; a heavenly chameleon, The airy child of vapor and the sun, Brought forth in purple, cradled in vermillion, Baptized in molten gold, and swathed in dun, Glittering like crescents o'er a Turk's pavilion, And blending every color into one, Just like a black eye in a recent scuffle, (For sometimes we must box without the muffle.)" Brewster reduces the seven prismatic colors to three prim- itive colors, red, yellow and blue. Each of the colors formed by the spectrum has different heating powers, independently of those of light ; the blue and green being the coolest. TKermometrical observations have determined the relative heating powers of these three primitive colors, as shown in the annexed scale : Blue rays Yellow - - 62 V Fanrenheit. Red The varied tints and colors of objects that we behold are not inherent in them as is generally supposed. It is the action of matter upon light, decomposing it, attracting certain of the prismatic colors, and reflecting others, that produces color. Most bodies act, as w^e have seen the prism, by dividing white light into its component paijts ; they then absorb, or they transmit, certain rays, and throw back the remainder. If we assert a body is of an orange color, we mean to say it reflects the orange ray. Objects that are black absorb all the colors, while those that are white, reflect them all. Green cloth ab- sorbs all the colors but green, which it throws back. So blue cloth absorbs all the colors but blue, which it reflects. OPTICS. 33 Recent investigations have established the fact that certain of tlie prismatic rays possess the property of communicating magnetism. A needle having been exposed to the violet rays for two hours acquired north polarity. The indigo, blue and green, produced the same effect, but in a less degree. The yellow, orange, and red rays appeared to be destitute of this power. Professor Farrada}^ is now engaged in a series of ex- periments on this curious and interesting subject. FORMATION OF IMAGES. If we make a hole in the shutter of a room, and hold a sheet of paper a short distance from it, an image of the objects on the outside will be depicted on the paper. This is the simplest way in which images can be produced. Or, if we take a box with a hole in one end of it at A., as re- presented in the Figure we will perceive that an inverted image of the object B. C. will be formed at the back of the box b. c. The ra3^s from the object B. C. pass in straight lines through the hole A. to form the image. It is evident the image must be upside down, because the rays from the upper end B., of the object cannot be bent to the upper end of the image at c. If we now en- ' large the aperture A., and place a double convex lens in it, we shall have the image brighter and more distinct. 3 34 OPTICS. -^ , When the image b. c. is received on a smooth white surface at the back of the box, the apparatus is termed a camera-oh- scura, but when the eye is placed behind the lens and sees the image in the air, the instrument is called a telescope. The principle of the telescope is this : the object glass forms in its focus a distinct image, which though smaller than the object, is yet seen under a much greater angle, or magnified, and the image so magnified is seen under a still greater angle, or still farther magnified by the eye-glass which enables the eye to see distinctly at a less distance than six inches. The Daguerreotype, one of the most remarkable and beau- tiful discoveries of this age of inventions, enables us to fix on metal plates the images derived from the camera obscura. This ingenious process has been brought to great perfection in this country. The portraits exhibited by Mr. M. B. Brady, at his gallery 205 Broadway, are especially deserving of atten- tion. They attract and command the admiration of the artist and connisseur. He seems to be particularly happy in creating beautiful and life-like pictures, entirely obviating the ghastly appearance presented in some impressions. The modus ope- randi is very curious: a piece of copper, plated with silver, is cleansed and polished with dilute nitric acid, after which it is exposed to the vapour of iodine, which gives it a yellow color, and upon this surface the rays of light of the object are im- pinged by the camera obscura ; the plate is then subjected to the action of the vapour oi mercury ; it is next washed with a solution of hypo-sulphate of soda and then with boiling water. When dry we have a perfect picture of the object intended to be delineated, but without color, further than degrees of shade. By the introduction of Bromine and other chemicals, a great improvement has recently been effected in the ait of taking perfect pictures, and the time of sitting]? now reduced to a few seconds. OPTICS. 35 These preparations greatly increase the sensibility of the plate to light, consequently the contrast between the white and dark places is more marked. The application of Bromine causes the rapid reception of the image on the plate, and pro* duces the deep black shades of an object. This is a very de- cided advantage, as the countenance preserves its natural ap- pearance for a short period only, and becomes constrained and unnnatural if the time of sitting is much extended. A long sitting has also the effect of rendering the picture bluish where it ought to be w^hite, and brown where it should be dark. Chloride of gold is ver}^ successfully used to fix and enliven the tints of a picture. By the apphcation of various pigment powders to Daguerreotype pictures, the appearance of colored miniatures has been closely imitated. The best pictures, it is said, are taken from an hour after the sun rises till he comes within 45^ of the meridian, and again after he has, passed the meridian by 45^. Photography, Calotype, Chrysotype, and Cyanotype, are various modifications of the art of making pictorial impressions of objects by the action of fight upon paper. The ray of light which is perpendicular, passes straight through the lens, while the lateral rays, passing obliquely, are converged by the lens to their focal point at P. The more convex the lens is the nearer will be its focal point, and the flatter it is the greater distance off will be the focus. 86 OPTICS. A double concave leus refracts rays in the contrary di- rection, that is to say, instead of coming to a focus, they diverge as they proceed. Hereafter we shall see the close connexion that exists be- tween the laws of optics on which we have touched and those which govern vision, and we shall thereby be the better enabled to understand the causes of near sight and far sight, and tlie reason why those imperfections are reUeved by the use of con- cave or convex glasses. It would be foreign to the plan of this little work to have en- tered more deeply into this part of our subject, but thus much was necessary for its elucidation. VERTICAL SECTION OF THE EYE. EXPLANATION, 1. Conjunctiva covering the cornea, 2. Cornea, or clear part of the eye. 3. Sclerotic, of white of the eye. 4. Membrane of the aqueous humour, or inner lining of the chamber. 5. Choroid, or vascular coat. 6. Retina, or nervous expansion. 7. CiUary processes. 8. Iris, or colored curtain of eye with pupil in csntre, 9. Crystaline lens, or principal magnifier. 10. Vitreous humour, forming principle bulk of eye. 11. Optic nerve. 12. Anterior chamber. 13. Posterior chamber. 38 ANATOMY OF THE ElE. THE EYE. Previous to making any application to vision of those op- tical principles at which we have thus briefly glanced, it be- comes necessary to give a short description of the Human Eye, and the parts composing and connected with it. The Eye is nearly round in shape, with a slight projection in front — hence commonly called the eye-ball or globe of the Eye. This particular form is the very best that could be con- trived to enable it to move about with the greatest facility and rapidity. The Eye consists of three orders or classes of parts ; — the first admit and modify the rays of light ; the second receive and carry the impressions to the brain ; and the third keep those organs in a fitting state to fulfil their functions. The Eye is protected on all sides by the bony socket, in which it is lodged, except in front, and here we have the eye- • lids like watchful sentinels, ever on the alert, to guard and protect it from approaching danger. The Eye is composed of four coats: — the Sclerotic, the Choroid, the Retina, and the Cornea, and three humours — the Aqueous, the Vitreous, and the Chrystalline. ANATOMY OP THE EYE. 39 These humours or lenses are transparent and very delicate, and require to be protected and supported by some strong sub- stance. For this purpose we have the outer coat or case, termed the Sclerotic^ or the "white of the Eye." It is a strong and dense substance, and extends, surrounding the eye, from the optic nerve behind to the Cornea in front. Here it is cut off and bevelled, so as to allow the Coraea to fit into it, as a watch glass into its case. The Sclerotic is opaque, it being necessary not to admit any light except through the pupil, just as the optician finds it essential to make the case for his telescope impervious to hght, and it is cut off before to allow a space for the transparent membrane — the Cornea. We shall hereafter see that the muscles which give motion to the ball are attached to this case. The Sclerotic in fishes is veiy dense and strong ; and in many birds it consists of three layers, the middle one being formed of bony plates. The Cornea is the clear, poHshed and brilliant substance that forms the front of the Eye. It is very tough and strong, so as to protect the parts within ; and yet it is perfectly trans- parent to admit the rays of light, which are here first refracted. Within the Sclerotic Ues the Choroid, which, like the former is wanting in front. It is very fine and delicate, and full of blood vessels. These secrete a dark coloring matter, the Pigmentum Nigrum, with which its entire inner surface is coated or painted. This dark substance absorbs all the superfluous rays of light. It is wanting in the Albino and in animals of prey. These cannot see distinctly in a bright, strong Hght, but in darker situations their eyes concentrate and reflect the light, and their power of vision is then much more acute. The eyes of cats, aud such animals, appear in the dark to glow with a particular ferocity : this is not owing to the animals being excited, but is occasioned by the want of this dark pigment. The Choroid, externally, seems to termi- W ANATOMY OF THE EYE. nate in front, where the Sclerotic and Cornea are joined to- gether ; and where it is connected with a white ring or hga- raent, but it extends inwards in the form of 60 or 70 beautiful folds, or processes, called the Ciliary. These are arranged in a radiated manner around the lens, on the front of the vitreous humour : each of these folds is covered with the dark pigment, similar to the choroid itself. Interior to the Choroid is the Retina : this is an expansion of nervous matter connected with the optic neiTe. It is a thin and delicate hiembrane, which commences at the optic nerve, and extends around the sides of the vitreous humour, nearly as far forward as the lens. It can be divided into three la5^ers. The external or serous was discovered by my old preceptor, Dr. Jacob, and called after him the memhrana Jacobi, or membrane of Jacob. It is extremely delicate and fine. The second, or nervous, is soft and gray ; and the internal is vas- cular. The retina is, as we have observed above, the nervous expansion, and on it the inverted image of the object we look at is depicted, just as we have seen in the camera obscura. We have said the humours of the Eye are three in number — the Aqueous, Vitreous, and Crystalline. The Aqueous humor is a clear watery fluid, as its name implies ; it is situated immediately behind the cornea, which it distends and supports. This fluid passes from the front to the back chamber of the eye through the pupil ; it aids slightly in refraction. There is a beautiful provision made (the mem- brane of the aqueous humor) whereby if it is lost through a wound of the cornea, it is again renewed within a few hours. The Aqueous humor is also of great use in supporting and en- abhng the iris to float about with perfect freedom. The Iris is the colored curtain which we see on looking into ANATOMY OF THE EYE. 41 the eye. It derives its name of iris or rainbow from the variety of colors it presents. It is a flat membrane, circular in foiTO, with a round aperture in the centre : this is the black spot, termed the pupil, or sight of the eye. The iris divides the eye into a front and back chamber, and these communicate through the central aperture — the pupil. The iris is very important to vision ; it acts as a curtain, regulating the quantity of light that is admitted to the eye, so that the pupil contracts in bright light, and enlarges in darkness or in moderate light. This can be observed by sitting opposite to a mirror and closing the eyes for a few seconds ; then, suddenly opening them, we will see that, in the interval, the pupil has become much en- larged and now quickly diminishes. The color of the iris varies in diiferent individuals. There are some persons who have one of their eyes blue and the other black, and instances have occurred in which the upper half of the iris has been gray while the lower part was brown. Occasionally the fibres assume an irregular shape so as to give an appearance remotely resembling the letters of the alphabet. A child was some time ago exhibited in France and England, on whose iris it was stated the words " Napo- leon Empereur" could be plainly discerned. A strong ima- gination, or a little credulity, perhaps, was necessary to ena- ble the wonder-loving and the curious to decipher the magic words. It is to the Iris that the eye owes its greatest attraction. Poets have sung of the beauty of the black, the blue, and the gray. Lord Byron says, — " Blue eyes, or gray, The last, if they have soul, are quite as good, Or better as the best examples say : Napoleon's, Mary's (Q,ueen of Scotland) should Lend to that color a transcendent ray ; And Pallas also sanctions the same hue— Too wise to look through optics black or blue." 42 ANATOMY OF THE EYE. The Chrystalline humour or lens is a transparent body of considerable firmness, having the form of a double convex lens, and is placed perpendicularly behind the pupil : it is im- bedded in the forepart of the vitieous humor. The lens is the principal magnifier of the eye. The third, or vitreous humor, forms the main bulk of the globe of the eye, filling its two posterior thirds; it is thin and watery, but is contained in numerous cells which prevent its running out when cut or woundp/^ ANATOMY OP THE EYE. 43 We will now consider what provision nature has made to preserve and keep this beautiful organ in order. We have already alluded to the protection which the eye receives from the bony cavity in which it is lodged. Our attention is next attracted to the eye-lids. These vigilant guardians protect the eye from danger, con- trol the quantity of light that is admitted, and by their link- ing motion keep it moist and bright, and wipe away dust or any extraneous matter. A thin plate of cartilage, the tarsus^ is added to the other textures that compose the eyelids ; this gives them a proper degree of firmness, and as it is thicker towards the margin of the lids it assists in supporting the eye- lashes. Near the edge of each lid, at the root of the hairs, are a number of small glands, the meibomian, which secrete a semi- fluid substance that assists in lubricating the surface and pre- venting the tears from running over on the cheeks. There is a minute hole at the inner angle of each eyelid : these lead by small passages into the lacrymal sac, and this communicates with the nose. When the eyelids are closed they form at their margin a channel through which the tears pass into these little openings and from thence into the nose. At the inner angle of each eye is a small reddish body, termed the caruncula lacrymalis ; it secretes a fluid which aids in keeping the eye moist. 44 ANATOMY OF THE EYE. The eyelids are beautifully fringed with the Cilia^ or eye- lashes ; those of the upper lid curve upwards, those of the lower lid downwards. The eye-lashes defend the eye from dust, and also modify the rays of light ; they add much to the expression of the eye — " In whose silk shadow lies Deepest attraction, for when to the view Forth-from its raven fringe the full glance flies, Ne'er with such force the swiftest arrow flew." — Byron. The eyelids are closed by a muscle which surrounds the eye, the orbicularis palpebrarum^ and are opened by the levator palpebrcB, a muscle which stretches from the bony socket, and is connected with the upper lid ; by its contraction the lid is elevated. We perceive that the eye-brow is also provided with hairs ; these are placed in an oblique direction, and prevent the per- spiration from the brow running into the eyes. The lacrymal gland is placed under the fore part of the upper eye-lid ; it secretes the tears which are poured out by a number of small ducts over the surface of the cornea. This preserves the part in a moist state, removes dust, or any thing which may accidentally enter the eye, and prevents the friction of the lids on the baU. By the motion of the lids the tears are constantly diffused over the surface of the eye. Next we observe a mucous membrane or skin lining each lid, and covering the front of the globe, and continued through the tear passage into the nose. This, which is termed the Con- junctiva^ joins the eye-lids to the eyes, supports and confines the eye-ball in its several motions, and closes the orbit against any foreign substance. ANATOMY OF THE EYE. 45 MUSCLES OF THE EYE. We have now to speak of the arrangement for moving this instrument in all directions. There are six muscles to eacli eye, four named from their form and position straight, and two oblique. The four straight muscles are attached behind to the bone around the entrance of the optic nerve, and before to the sclerotic coat of the eye, one above to elevate, one below to de- press ; one on each side to direct the eye outwards or inwards. The upper oblique muscle arises from the bone behind, and passing forward ends in a round tendon which plays through a pulley and then bends back and is inserted into the sclerotic. Its use is to rotate the eye. From the peculiar expression of countenance which the action of this muscle produces, Dr. Jacob very appropriately termed it the pathetic. The lower oblique commences at the front and lower part of the orbit, and ascending backwards and outwards, is attached to the sclerotic ; this also assists in the rotary motion. By means of these muscles we are enabled to move the eye in all directions with the greatest facility and correctness. The muscles derive all their motive power from the nerves, without which they would be utterly impotent. The optic nerves, or the nerves of vision, take their origin from the lower part of the brain, and pass forward, convergmg towards each other till they meet, where they decussate or cross each other ; 46 ANATOMY OF THE EYE. they then separate, and each proceeds forwards aad outwards to the back of the orbit, which they enter through a round hole in the bone {the for amen opticum), and piejcing the sclerotic and choroid coats, terminate in the cup-shaped expansion — tbe thin and dehcate retina. The optic nerves are not the only neiTes connected with vision, for the eye and its surrounding parts are abundantly supplied with nerves derived from other sources. These serve to give the muscles voluntary motion, and some to assist in the various functions of the organ. The branches of the fifth pair of nerves, which are distributed to the nose, are also connected with the respiratory system. When, therefore, these are irritated, sneez- ing is produced. We sometimes, on looking suddenly at the sun, sneeze. This is owing to a small branch of the fifth pair of nerves, which connects with the lacrymal gland and the Schneiderian membrane or the lining of the nose. From the same cause, if the tip of the nose is pulled, or irritated, the eye sheds tears. The eye is also very freely supplied with blood-vessels. The middle, or choroid coat, is almost exclusively formed of a tissue of blood-vessels ; these secrete the dark pigment, of which we have already spoken. The tortuous course which the ciliary arteries pursue, in passing forward to the ciliary processes, is very remarkable, as by this arrangement no obstruction is offered when the crystalline lens is brought forward in its ad- justment to different distances. PHYSIOLOGY OF THE EYE. 47 PHYSIOLOGY OF THE EYE. Having now seen the parts that compose this instrument, we will briefly point out how vision is produced. The convexity of the cornea and the lens, and the density of the different hu- mours, is such that when parallel rays of Hght fall upon the cornea and pass through the pupil they are brought to an exact focus on the retina, where an inverted image is depicted of the object towards which the eye is directed. This can be proved by cutting or paring away a portion of the sclerotic coat of the eye of an ox, and holding it up at the window, when we will behold an inverted picture of whatever object we direct the eye towards. We may now perceive that the organ acts altogether me- chanically, the rays of hght being affected by the humours through which they pass, exactly in the same manner as if they had been transmitted through a convex lens. But the eye is greatly superior to any optical instrument, in- asmuch as it is entirely free from spherical and chromatic ab- erration. 4B PHYSIOLOGY OF THE EYE. The impression made by the rays of light on the retina is conveyed along the optic nerve which meets and interlaces with the one of the opposite side, as exhibited in the engraving. They then separate, and each proceeding to the brain, vision is produced. The retina retains the impression of light made on it for some time after the cause has been removed. This is proved if a burning body is rapidly whirled around, for the eye per- ceives a complete and unbroken circle of light. Prom the same cause the seven prismatic colors, as we have seen, when painted on a wheel, and rapidly revolved, assume a white color. No separate color will be seen, but the eye will receive the general sensation of whiteness from the combined impression of the whole. This pecuUarity of the eye has been ingeniously used in the construction of the Thaumatrope and other toys. On a round piece of Card is painted a carriage, and on the reverse side the driver ; to the circular card is attached two silk strings, when twisted with the fingers so as to revolve with great velocity we see the coachman in the attitude of driving, in other words, we see at the same time what is drawn on both sides of the card. PHYSIOLOGY OF THE EYE. 49 There is a curious phenomenon appertaining to the eye, by which it sees accidental colors. If we close one eye, and look steadily for some time at a red wafer on a sheet of white paper, and then turn the same eye to another part of the paper, we shall see a green wafer : this green image is termed an ocular spectrum. If we use different colored wafers, the following will be the result : — Black. White, White, Black, Red, Blueish Green, Orange, Blue, Yellow, Indigo. This peculiarity is caused by the retina being unable to per- severe in the same kind of action beyond a certain period, and the spectral color is always that which would result from a union of all the prismatic colours except the one to which the eye had been previously exposed, and to the action of which it had consequently become more or less insensible. Doubtless, as an intelligent writer observes, the harmony of colors and the richness of effect, as exhibited in pictures, or in the arrangement of drapery or furniture, depends in a great de- gree on these ocular spectra, or accidental or opposite colors, the brilliancy of the colors being much increased by the position in which they stand opposite to each other. By means of pressure on the eye-ball, ocular spectra may be produced. In particular states of the stomach, the pressure of blood-vessels on the back of the retina often produces spectra ; in slight affections these resemble lioating masses of blue light, appearing and disappearing ; in some cases they become green a^d occasionally yellow. These sometimes may have given rise to the behef in supernatural appearances, even after the 50 PHYSIOLOGY OP THE EYE. exciting cause is removed the spectrum will often still remain visible, and the mental powers themselves being perhaps also weakened, render them peculiarly susceptible of being affected by superstition and credulity. If the e}^e is steadily directed to objects illuminated by a feeble light, it causes as much pain as is produced by an excess of light, a kind of remission takes place in the conveyance of the impressions along the nervous membrane, the object actually disappears, and the eye is agitated by the recurrence of im- pressions which are too feeble for the performance of its func- tions. Brewster says that this may serve to explain some of the phenomena of the disappearance and re-appearance of ob- jects, and the change of shape of inanimate objects, which have been ascribed by the ignorant to supernatural causes, and by philosophers to the activity of the imagination. If in a dark night, for example, we unexpectedly get a glimpse of any ob- ject, either in motion or at rest, we are naturally anxious to ascertain what it is, and our curiosity calls forth all our powers of vision. This anxiety, however, serves only to baffle us in our attempts. Excited by feeble illumination, the retina is not capable of affording permanent vision of the object ; and while we are straining our eyes to discover its nature, it will entirely disappear and afterwards re-appear, and vanish alternately. The same phenomenan may be observed in day-light by the sportsman when he endeavours to mark on the monotonous heath the particular spot where game has alighted. Availing himself of the slightest difference of tints in the adjacent heath, he keeps his eye steadily fixed upon it as he advances, but whenever the contrast of illumination is feeble he invariably loses sight of his mark, and if the retina is again capable of taking it up it is only to lose it a second time. A singular affection of insensibility to certain colors, ha» been observed in several cases, where vision w^as otherwise PHYSIOLOGY OP THE EYE. 0| peifectj and it would seem to be hereditary. Some can only distinguish white and black. There is a curious case related in the Edinburgh Transactions, of a tailor who could only dis- tinguish with certainty white, yellow, and gray. On one occa- sion he repaired an article of dress with ciimson instead of black silk, and at another time he patched the elbow of a blue coat with a piece of crimson cloth. Another case is recorded where a naval officer purchased a blue uniform coat and waistcoat, with red breeches to match the blue coat. And a well authenticated anecdote is told somewhere, by Dr. Priestley, if I remember right, of an artist, who was en- tirely unable to distinguish some colors. He was therefore obhged to keep them in a certain series or order, as the only means by which he could discriminate between them. His companions sometimes amused themselves by disarranging this order, and the unconscious artist would thus give a gentleman a green beard or moustache, and adorn a beautiful young lady with a pair of blue cheeks. With regard to the apparent magnitude of objects at a dis- tance, there is no doubt we judge of them by experience and association. We calculate their apparent size from what we know to be their real size, the distinctness with which they are seen, the vividness of their colors, the number of intervening objects, and our supposed knowledge of their distance. The arts of landscape and architectural painting, and still more remarkably the science of perspective, depend entirely upon the principle that we judge of the size of objects by their distance. If the artist is able to convey to our minds a correct conception of the position in which the different objects are sup- posed to stand with respect to each other, we immediately con- 52 PHYSIOLOGY OF THE EYE. ceive of them as presenting the size that they actually possess, without any relation to the space which they occupy on the canvass. In blind persons the sense of touch supplies many of the im- pressions which, under ordinary circumstances, are produced by sight. The bHnd will sometimes estimate, with considerable correctness, the size of apartments. This knowledge the}^ ac- quire by attending to the force of the reverberation which is produced from the walls, and it depends upon their comparing the effect thus produced upon the ear, in the case under consi- deration, with their previous experience in similar circum- stances. With regard to Singleness of Vision^ we observe that when both eyes are directed to an object, a separate image is formed upon each retina ; yet the mind forms only the conception of one object. This is invariable, except where disease or acci- dent prevents the eyes from moving in concert — as in delirium and intoxication. When the usual train of associations is in- terrupted, double vision is sometimes produced. In such cases the eyes do not move in a parallel direction, and consequently, the impressions are not made on corresponding parts of the retina. The eye, when in a state of repose, is adjusted to remote ob- jects. When we wish to view near objects, we use a volun- tary exertion, by which we bring forward the crystalline lens, and thus we perceive how admirable is the organization by which the eye instantaneously adapts itself to every degree of distance. DISEASES OF THE EYE. We shall now proceed to give a short description of the Diseases of the Eye. Ophthalmia^ which is derived from the Greek ^ xmx'zx.G-r 10,1x1 ili-h x or Vioion. human suffering. How toucliingly has Milton depicted his melancholy condition under this sad privation : " With the year Seasons return : but not to me returns Day, or the sweet approach of even or mom, Or sight of vernal bloom, or summer's rose, Or flocks, or herds, or human face divine ; But cloud instead, and ever-during dark Surrounds me, from the cheerful w^ays of men Cut off, and for the book of knowledge fair Presented with an universal blank Of nature's works, to me expunged and razed, And wisdom, at one entrance, quite shut out. It cannot he too clearly understood that the influence of the \ mind, the general health of the system, constitutional causes. \ the state of the blood, stomach and digestive powers, have an \ intimate and important bearing on the condition and well-being of the organs of vision. To preserve the " mens sana in corpore sano," a sound mind in a sound body, is then a matter of the first consequence. We will therefore suggest what we deem most likely to accomphsh BO desirable a purpose. TEMPERANCE. The first great rule is temperance in all things. I need scarcely enumerate the train of ill consequences attendant on drunkenness, at such a tale as this even death himself grins horribly/ a ghastly s?nile. Death lies concealed in the tank- ard that waits beside the drunkard ; and death has taken up his abode in the glass that sparkles in the hand of the dram drinker. And if some persons will be so fool-liardy as to devour death, they must abide the dreadful consequences. The in- PRESERVATION AND IMPROVEMENT OF VISION. ^5 temperate not only, however, shorten their own days, but by transmitting a morbid stamina to their descendants subject them to disease and untimely dissolution. Alcohol, when taken into the stomach, is absorbed and gets into the circulating system; a portion of it escapes by the lungs and is recognised by its odor in the breath. Liebcg asserts that it is burnt in the lungs and thereby converted into carbonic acid and water. Alcohol, therefore, is a fuel in the animal economy, by the combustion of which caloric is evolved, but it is a most obnoxious and dangerous fuel. Its volatility and the facility with which it permeates membranes and tissues enables it to be rapidly absorbed, and when it gets into the blood it exerts a most injurious operation on the brain and the liver. But if temperance is desirable for the general benefit of the system, it is eminently so with regard to the organs of vision, for no where are the effects of intemperance more strongly marked than in the eyes, from the period when the sometime inebriate sees all objects double, to that of the red and bleared eyes of the confirmed and habitual drunkard. REGULAR HOURS. " Early to bed and early to rise, Makes a man healthy, wealthy, and wisQ. may be a trite, but is a veiy true adage. To retire at a proper hour, rest a sufficient period, and rise betimes, produces a salu- tary influence on the delicate eye ; but he who converts night into day, sitting up in crowded and badly ventilated apart- 94 PRESERVATION AND IMPROVEMENT OF VISION. ments, surrounded, perhaps, by glaring lights, will probably soon perceive the red and weakened appearance presented by this sensitive organ, and thus be admonished of the injury he is inflicting on it. Retiring early to rest, breathing a free air in the night, with- out the interruption of bed curtains ; rising early in the morn- ing as soon as nature is refreshed, and getting out, if possible, into the country, or outskirts of the town to inhale the pure air. contributes to give elasticity to the springs of life and renovates the entire system. Nothing is more weakening than the habit of laying in bed after nature has been refreshed by invigorating sleep. The following extract from the Journal of the celebrated Elizabeth Woodville, afterwards married to Lord Grey, and subsequently Queen to Edward IV. which was extracted from an ancient manuscript, preserved in Drummond Castle, nlay surprise, amuse, and perhaps profit some of my young readers : Monday Morning. — Rose diifour o^ clock, and helped Cathe- rine to milk the cows ; Rachel, the other dairy-maid, having scalded her hand in so bad a manner the night before. Made a poultice for Rachel, and gave Robin a penny to get some- thing from the apothecary. Six 0^ clock. — The buttock of beef too much boiled, and beer a little of the stalest. Mem. To talk with the cook about the first fault, and to mend the second myself by tapping a fresh barrel directly. Seven. — Went to walk with the lady my mother in the court-yard, fed 25 men and women ; chid Roger severely for expressing some ill will at attending us with the broken-meat. Eight. — Went into the paddock behind the house with my PRESERVATION AND IMPROVEMENT OP VISION. 96 maid Dorothy ; caught Thump, the little poney, myself, and rode a matter of six miles without saddle or bridle. Ten. — Went to dinner. Eleven. — Rose from the table, the company all desirous of walking into the fields. John Grey would Uft me over every stile. Three. — Poor farmer Robinson's house burnt down by acci dental fire; John Grey proposed a subscription among the company, and gave no less than four pounds with this bene- volent intent. Mem. Never saw him look so comely as at that moment. Four. — Went to prayers. Six. — Fed the hogs and poultry. Seven.—Su^^QX on the table ; delayed till that hour on ac- count of farmer Robinson' s misfortune. jVme.— The company fast asleep. These late hours very disagreeable ! CLOTHING. Comfortable and suflScient clothing, adapted to the seasons, is of vast importance, especially to childien and aged persons. It is a very mistaken notion to endeavor to make children hardy by exposing them to cold, or depriving them of warm clothing. Such a course is much more hkely to engender 96 PRESERVATION AND IMPROVEMENT OF VISION. dfeease than to promote health. Above all things it is neces- sary to keep the feet dry and warm. Damp feet are a prolific source of many of the various ailments to which the eyes are liable. Clothing in itself has not the power of communicating warmth, it prevents the escape of the natural caloric of the body, and thus a stratum of warm air is retained between the clothes and the body. This explains the cause of loose gar- ments being warmer than tight ones, because the loose dress, if closed at its upper and lower part, encloses a thin stratum of warm air which the tight one cannot. Every extra article of clothing which we put on creates an additional layer of warm air, the outer layer being cooler than the inner; there- fore when v/e are about to go out into the cold air, we ought to put on our outside garments a little before leaving the warm room, so as to heat the outer layer of air, as otherwise the heat will be withdrawn from the body itself The materials used for clothing should be bad conductors of heat and of sufficient permeability to allow free transpiration of the skin. Woollen and silken articles of attire cause in some persons of sensitive skin cutaneous irritation and even eruptions. Linen is very agreeable next the skin, but it absorbs the perspiration, and instead of the stratum of dry air. there is one of moisture, and this being a good conductor of heat, rapidly chills the body. Cotton, though not so pleasant to the skin, is preferred in warm weather, as it does not absorb moisture to the same extent as linen. Great attention should be paid to frequently exchanging foul linen and flannels for those that are cleanly washed and well dried, and this part of advice respects both body and bed- clothes. Nothing renders clothes purer or sweeter than good country washing and bleaching. It would not be an excess of cleanliness but tend greatly to the preservation of health, if in PRESERVATION AND IMPROVI<:MENT OF VISION. 97 addition to the rule of never using- the same inner garments by day and night, those persons who wear flannel vests would change them every day. This may be done without much trouble or expense, by having two vests in use at the same time, and wearing them alternately, hanging up the one that was last worn to air during the time it lemains unused. So much has been said and written relative to the injurious effects of tight clothes, especially the deformity-creating corset, that I will add nothing more than to protest against folly so absurd. I believe most persons now understand the misery that those instruments of torture entail to the third and fourth generation ; but so despotic is the empire of fashion that they kiss the tyrant hand which smites them. " They know the right, and they approve it too, Condemn the wrong, and yet the wrong pursue !" With regard to colors, it is very important that persons who have a tendency to weakness of the sight should select those of soft and refreshing hues, and not such as reflect the bright and heating rays. Ladies' bonnets, under such circumstances, should be blue, green, grey, or black, particularly the lining. Bright and glaring flowers, or ribbons, on the inside of the bonnet are very trying to the eyes, as well as similar colors in parasols, sun- shades and fans. Veils are decidedly objectionable, they pre- vent the free circulation gf air, and from their constant waving to and fro vision is rendered confused and indistinct. 7 98 PRESERVATION AND IMPROVEMENT OF VISION THE BATH. Next is the cardinal virtue of cleanliness and frequent ab- lutions of the entire person. Water conduces, in an eminent degree, to health and happiness. A bath every morning in the year, of warm or cold water, the latter if the constitution is not too feeble, will be found the beet preservative against colds and inflammations of the eyes. The temperature of the water ouglit to be regulated by the feehngs of the individual. The great test of its benefit is if after the bath a delightful glow is felt to pervade the whole body. We know that in a state of health insensible perspiration is continually taking place. We are told that each cuticular pore that exhales this secretion has a little tube attached to it of about a quarter of an inch in length, and that there are 3,258 of these in a square inch on the palm of the hand or a length of tube equal to 73 1-2 feet. But even estimating the number of pores in each at 2,800, anc^ calculating the number of square inches of surface in an ordinary sized man at 2,500, it follows that if these little tubes were extended out in a con- tinuous line, they would reach the enormous length of 28 miles ! And it has been calculated that eight grains in ^veight of perspiration are exhaled by the skin through these pores in the course of a minute. PRESERVATION AND IMPROVEMENT OF VISION. 99 We also know that the outer or scarf skin is constantly thrown off from the body in the shape of small powdery scales. These become mixed with the unctuous and saline products of the skin, and when united together they form a thin pellicle to which dust and dirt adhere. This concretion blocks up the pores, prevents free transpiration, irritates the skin, and keeps it damp and cold. The insensible perspirafion being thus checked in its egress, the destructive fluids and impurities which ought to pass off in this way are again taken up into the sys- tem, giving origin to various maladies of the different organs and tissues, and this is oftener than is generally supposed the cause of diseases in the eye. The skin likewise performs in the animal economy an im- portant part as a respiratory apparatus ; but if the pores are stopped by these accumulated secretions, the blood cannot be oxidized on the surface of the body by the air. neither can it here discharge its carbon, thus suspending or annulling over so great an extent of surface a function of such vital importance. The incrustation is, also, a nucleous, where miasma and in- fectious matter may lodge until it is absorbed into the system, producing not unfrequently death and destruction. Siuely no argument is necessary after this statement of facts to enforce the absolute necessity of the bath, for this effectually removes incrustations, frees the pores from obstructions, and by its habitual use we are enabled at all times to secure a free transit to the natural exhalation, promote a copious discharge of insensible perspiration, prevent the blood from being poi- soned by the re-absorption of impurities, and essentially add to the health and happiness of the individual. Those that have used this salutary process for any time could not easily be in- duced to relinquish a prac.tice that tends to render the body indurate against cold, and is fraught with so many other ad- 100 PRESERVATION AND IMPROVEMENT OF VISION. vantages. In fact nothing is more refreshing or hixurious after fatigue and exhaustion than the bath, or more speedily revives and restores the drooping energies, exiiihrating the spirits and giving renewed tone and vigor to the entire system. The shower bath possesses in some cases many advantages, and from its portabihty and general utihty is fast becoming a sine qua non in every dwelHng. The gentle shock to the ner- vous system, and the concussion of the skin, caused by the fail of the water, produces a highly salutary effect. Reaction quickly follows the first sensation of cold, for this is speedily succeeded by an agreeable feeling of warmth. The shower bath is particularly useful in diminishing the sensibility of the skin to the impressions of our changeful climate. But this, like all other baths, ought not to be used violently, that is to say, the shock ought not to be too severe either in quantity or tem- perature. A gradual course of training from tepid to cold is ob- viously the most prudent method. Some invalids bear the cold shower bath much better by having their feet immersed in warm water while taking the shov/er. Many persons having asked my opinion relative to the merits of the various shower baths now before the public, I took par- ticular pains to examine the peculiarities of each. The resu-lt is that I most decidedly give the preference to " Locke's Pa- tent " (31 Ann street) I unhesitatingly recommend it as the ne plus ultra of baths. It combines economy, durability, sim- plicity and portability, and superadded to those requisites are some remarkable advantages. It can be used as a Douche, vapor, or hip bath, and, also, it may be said to obviate the necessity of the cumbersome batliing tub. At my suggestion Mr. Locke has further added to its usefulness by having a fine tube connected with the reservoir, and in this way a beautiful jet of water is formed which answers an excellent purpose as an eye fountain. Locke's shower bath is the best that has yet PRESERVATION AND IMPROVEMENT OF VISION. 161 been invented for enabling the beginner to undergo the gradual course of training that I before alluded to, as he can control the quantity of water and the elevation from which it falls. The cold plunge bath is somewhat similar in its effects to the shower bath, but not always so efficacious. The Douse or Douche-bath, is a contrivance for applying water locally, and combining with effusion more or less con- cussion of the skin. As the remedy for local disease, this form of bath has been used from time immemorial. A jug of water poured from a height on a part of the body is a Douche bath, and a more complete one is a stream from a pump — the popu- lar treatment for a sprain. No embrocation, lotion, or other remedy is as effectual in such cases as cold water thus applied. The concussion of the skin caused by the blow of the water against the surface is a feature of importance in this form of bath, and where a sufficient height of column or force could not be obtained the blow has sometimes been applied arti- ficially by a little wooden hammer with which the skin is beaten as the water falls. The jet of water, or the Douche-bath, is one of the most invaluable and appropriate remedies that can be used for strengthening and preserving the visual organs. Through all time water has been highly esteemed as the most useful and natural agent in various infirmities of the eyes, but in no way is its application so beneficial and invigorating as when a con- tinuous shower is allowed to play on the closed eye and sur- rounding parts for five or ten minutes at a time. I have succeeded in constructing a self-acting Eye Fountain, on sJmple hydrostatic principles. Tn this little machine, by means of pneumatic pressure, a considerable impetus is given to the water. The onlv trouble required before commencing 1V 102 PRESERVATION AND IMPROVEMENT OF VISION. its use is to charge it with pure water, either warm or cold, or with rose wat^r, which is sometimes agreeable and proper ; then hold the flexible tube opposite the closed eye^ turn the stopcock, and a fine continuous shower or stream issues from the pipe, which may be caused to strike against the outside of the eyelids, and the brow and temple, with increased or di- minished force as required, this being regulated by turning the faucit. The Fountain is exceedingly simple in its mechanism, and not liable to get out of order. The disputed point as to whether the application of water to the open eye is beneficial or otherwise, is, I think, very plainly solved by nature herself; for in this, as in many other Hygean rules, we must be governed by individual idiosyncracy or pecu- liarity. Many persons make it a daily practice to bathe their open eyes in a basin of water every morning, which strengthens and preserves their vision. In others, of sensitive eye or constitution, water, thus applied, would be too powerful a stimulant, and prove not only injurious but, perhaps, de- structive to the sight. So also with regard to the temperature of the water, to some, water at its lowest temperature would be appropriate and refreshing, while to others such a degree of cold would be not only painful but absolutely hurtful. In all cases we must appeal to our judgment and experience ; and, as I have elsewhere remarked, the feelings of the individual and the effects produced by such applications, are the surest and most unerring guides. Whatever discussion may arise as to the effects of water applied to the open or naked eye, there can be no question as to the great and unqualified advantage of its application ex- ternally, that is to say, to the integuments of the eye-lids and the adjacent parts, by means of the Self- Acting Eye Fountain, in a continuous and modified, but soothing stream, for it occa- PRESERVATION AND IMPROVEMENT OF VISION. sions neither contusion, chilliness, nor the slightest uneasiness, but on the contrary, a refreshing and invigorating coolness, 3oeedily followed by an agreeable glow, which imparts anima- tion to the countenance and increased energy to the visual, as well as muscular powers of the organ. The apparatus will be found eminently serviceable, not only to ladies who are in the habit of devoting a large portion of their evenings to reading, drawing, or fine needlework, but, also, to every description of artists, artizans and mechanics, such as miniature painters, engravers, watchmakers, jewellers, embroiderers, sempstresses, and all other persons whose avocations protracted frequently to late hours, compel them to long-continued inspection of iielicate, shining, or diminutive objects under the stimulating and exhausting influence of gas or other strong and reflected light. Whenever the eyes, in consequence of such unintermitt ;d and inordinate exertions experience a sensation of heat, we xk- ness, and tensive uneasiness, accompanied with unsteady ind confused vision, the eye-fountain aflbrds immediate reliefs and, by removing the inflammatory and relaxed condition of the organ prevents that impairment or total loss of sight, in which these symptoms, if neglected or improperly treated, are other- wise apt to terminate. The eye-fountain constitutes likewise a valuable and orna- mental appendage to the dressing-room ; the use of which for a few minutes before encountering boisterous winds, cold night air, or those atmospheric changes inseperable from attendance, in the evening at the houses of legislature or congress, at cha- pels, lectures, theatres or other places of public amusement, proves a ready and agreeable preservative against the occur- rence of a suffused, watery and painful state of the eyes, and occasionally worse functional derangements, which, without its assistance, such exposure is hable to induce. 104 PRESERVATION AND IMPROVEMENT OF VISION. The plain vapor and medicated vapor bath are excellent remedial measures in particular affections. By means of the latter the volatile principles of various medicinal substances can be introduced into the system. A cheap substitute for the vapor bath has recently been recommended. Take a piece of quick-lime about half the size of the hand, wrap around it a wet cloth sufficiently wrung to prevent water running from it, wrap a dry cloth several times around this ; prepare a second one in the same way : place one of the packets on each side of the patient when in bed. An abundant humid heat is soon developed by the combination of the lime with the w^ater, which quickly induces copious transpiration. The effect will last for two hours at least. When perspiration is fully established withdraw the lime which is now reduced to powder. With regard to temperature we must be governed in each instance by the nature of the case, the peculiarities of the pa- tient and the particular effect we are desirous of accomplishing. The temperate and the tepid bath produce a quieting or seda- tive effect on the system. The hot bath stimulates, and the warm bath has an intermediate action. The range of the several baths is by Fahrenheit's thermometer, as follows : Temperate from 75^ to 80^ Tepid from 85^ to 95^ Warm from 95^ to 98^ Hot from 98^ to 105^ The free use of soap to remove the accumulated oily matter secreted by the skin is absolutely requisite. After the bath, whatever it may have been, the body must be thoroughly dried and rubbed with a. coarse towel until a genial glow is diffused over the entire person. PEESERVATION AND IMPROVEMENT OF VISION. 105 Friction with the horse-Iiair gloves 'or straps will also be found singularly advantageous in determining the blood to the surface, and promoting a healthy reaction of the skin. The proper way to use them is, after the body has been thoroughly dried, to rub them briskly over the entire surface, but not too severely, for considerable injury may be inflicted on the skin by their unmerciful application. The glove ought not to be hard and unyielding. Those manufactured by Dinneford, and im- ported by Gumming, Dodge & Co., 43 Fulton street, and sold by all respectable druggists, are immeasurably superior to all others. In those gloves the points of the hair are perpendicu- lar to the surface, like a brush ; they are very soft and agree- able, and at the same time efficacious, and are not likely to in- jure the tenderest skin. There are some very beautiful ones expressly prepared for the use of ladies. The apartment in the house where the bath is taken should be airy and comfortably warm in winter. When a complete bath cannot be conveniently obtained, a wet sponge or sheet may be substituted ; this, though not so efficacious, is nevertheless very beneficial. The wet sponge should be quickly rubbed over the body, which must be as quickly dried. In many cases salt may be added to the water with good effect. The salt- water bath in the open sea, in pleasant weather, is superior to any other form of cold bath. The topical action of the salt-water is more stimulant than fresh water, from the na- ture of the saline particles that it contains, and from its greater weight, being about one-thirtieth part heavier it produces a greater degree of concussion. The reaction is almost immediate and certain, and conse- quently it may be indulged in a little longer than common water, and persons are less lively to take f old after it. 106 PRESERVATION AND IMPROVEMENT OF VISION. The tonic effects of the salt-water, the fine fresh air, and the exercise of swimming and moving about, combine to make it both exhilirating and^ invigorating. These good effects are, however, frequently diminished, or, indeed, positive evil is often produced, by remaining too long in the water. Prudence should, therefore, be exercised in this respect, as well as in choosing the most proper time for bathing. A bath ought not to be taken either immediately before or for several hours after any meal, and early in the morning is decidedly the most healthful time. The art of sv/imming is one of the most useful accomplish- ments a youth can acquire, for by it he may be enabled, in case of emergency, to save his own life or rescue that of a fel- low-creatuie from an untimely end. I will, therefui'e, say a few words on the subject. The principal thing required in learning to swim is confi- dence ; I therefore wish to impress upon the mind of the learner one or two philosophical facts. All bodies that float on the surface of the water, displace as much fluid as is equal in weight to the weight of the bodies ; therefore, in order that a vessel may keep above water, it is necessary that the vessel and its cargo should be of less weight than the weight of a quan- tity of water equal in bulk to the part of the vessel which is immerged in the water. Now, by actual experiment, it has been ascertained that the mean specific gravity of the human body is one-ninth less than that of common water, so that as we are specifically lighter than water, it only requires a little skill to enable us to float like a piece of wood, and this principally consists in occupying a proper position in the water ; the great desideratum is to lay perfectly extended, the whole body and limbs being kept under the water except the face, because the head, legs, and arms are heavier than the water, though the body is not, and consequently, if they are kept above the water they sink the body, just as too large a cargo would sink a ship. PRESERVATION AND IMPROVEMENT OF VISION. 107 A person who has not learned to swim endeavors to keep his head too much out of the water, and loosing his presence of mind throws his arms upwards, and by his efforts and struggles raises himself so high above the water that his body does not displace so much of the water as is equal to its weight, and he immediately sinks ; he takes water in by the mouth and nos- trils, which soon renders him as heavy as the surroimding ele- ment ; the coldness of the water, and, perhaps, his own fears have a tendency to contract the entire body, and, of course, to increase its weight in proportion to its bulk, and all these things combined causes a person to sink. But if the beginner will only recollect the fact of his body being in reality lighter than the water, the very knovvledge of this natural buoyancy ought to be sufficient to give him full confidence in his next attempt at sw^imming, and by trying to avoid all effort and laying flat with only his face above water he will soon be enabled to strike out gently with his hands and feet, and be gratified to find that he has already conquered what hitherto appeared to him almost an insurmountable difficulty. Young persons who cannot swim ought to be careful to as- certain the real depth of the w^ater before venturing to plunge in, for if the water be clear it appears less deep than it really is, because, according to the law of reflection, of which we before spoke, w^hen explaining the cause of an oar appearing to be crooked w hen immersed in clear water the image of the part or bottom lies above the object, hence the depth of a stream is one-fourth part greater than it appears to be ; in other w^ords, suppose the water to be six feet deep, on looking at the bottom it appears to be only four and-a-half from the surface. Those persons, who from want of time and opportunity can- not avail themselves of bathing in the open sea, can find a most admirable substitute in the excellent floating salt water baths of that respected and experienced veteran in the art of bathing, 108 PRESERVATION AND IMPROVEMENT OP VISION. Dr. Rabineaii ; indeed, I believe I will be doing good service by extracting a leaf from the Doctor's directions to his bathers : " While particular care should be taken never to go into the water in a state of extra perspiration or great heat, it is equally necessary to have a strict regard to a proper temperature of the body, so that being cautious of too great heat, we should be equally so of too much coolness. " If one rule should be urged upon the attention of bathers more strongly than others, it is that in coming to the bath, and being in a perspiration, they should never take off their coats or dresses, and remain sitting for a time to get cool, but rather remain with them on until they are in a proper temperature for the water, and that should ever be above the heat of the water, to have the most desirable effect. The best effect is lost in getting too cool before going in, and most certainly no good can be obtained by staying in too long." In connexion with this subject I may mention that hot salt water baths, so decidedly effectual in some cases, can only be procured in this city at Dr. Rabineau's establishment at the foot of Desbrosses street, and here they can be had throughout the entire year ; while at the Astor House, his warm, cold and shower baths, of the pure and limpid Croton, are attended with all the appliances and comforts that really make the bath not alone desirable but positively luxurious and truly healthful. PRESERVATION AND IMPROVEMENT OP VISION. 109 EXERCISE. Exercise is essential for the promotion and enjoyment of good health, whilst, on the contrary, sedentary habits are the fruitful source of numerous maladies, especially of the eyes. Exercise is a powerful means of strengthening sight and pre- venting disease. The experienced practitioner quickly dis- covers, by the peculiar unhealthy appearance of a patient, if his disease arises from want of proper exercise, and often, by inducing regularity in this respect, is enabled to remove the disease, or at least render it much more easily influenced by curative remedies. As a mode of exercise, w^alking is equal to any, and fortu- nately is accessible to all, whether poor or rich. In walking all the muscles are brought into play, and the dormant energy of nearly all the organs aroused ; the blood circulates with free- dom, the countenance is radiant with the tinge and glow of health, and the eyes sparkle with renewed lustre. But, walk- ing to be thus beneficial must not be pursued as a task, or taken with the spirit of martyrdom witli which we swallow a dose of salts, for the sake of the good to be accomplished ; nor yet will the daily pilgiimage from home to business, and from '• down town " and back again, secure this object. — Too well the care-worn visdge and hurried gait of the slaves to mammon demonstrate the inutility of exercise without 50?^/. This then, is the great desideratum ; the mind must be amused and the eye delighted with varying and novel scenes ; fresh country air clear sky, and green fields, particularly if enjoyed in the society 110 PRESERVATION AND IMPROVEMENT OF VISION. of a valued and cheerful friend, combine to render walking at- tractive, desirable and healthful. Every one has observed how much the pleasure of a pedes- trian excursion is increased if it be enlivened by the conversa- tion of an agreeable companion. The old Roman poet under- stood how much the wearisomeness of even a toilsome walk is beguiled by the society of a kindred sphit, when he wrote — " Comes jucundus pro vehiculo est." A pleasant companion is better than a carriage. Somewhat similar Avas the feeling of the French traveller who pathetically bewails the sad fate which compelled him to "wend his solitary way" through verdant meads and blooming landscapes. " O, ^quiH est triste de voir un beau jpays sans avoir personne a qui dire ' voila un beau pays P " Exercise on horseback possesses superior advantages in some cases, as it can be enjoyed by the invalid for a longer period without fatigue or weariness. Exercises which employ both body and mind in the open air, such as the manly and scientific game of cricket, throwing the quoit, leaping, running, and ascending heights, may be deemed the most effectual means of expanding the chest and promoting sound health. As many persons engaged in busi- ness or sedentary occupations cannot take all the exercise abroad that is necessary for their health, they ought, if possible, to visit a gymnastic establishment and there exercise mode- rately every day ; also use the dumb bells at home every morn- ing and evening, and walk about in their own stores or houses for at least an hour every da}^, for although such proceedings will not compensate for the loss of exercise out of doors they are the best substitute for it that under the circumstances can be resorted to. For young ladies the use of the skipping rope, PRESERVATION AND IMPROVEMENT OP VISION. Ill exercise with the shuttle-cock and battle-door, playing the graces, singing and reading aloud, dancing, and daily practice at the Kalisthenic Institute, will be found of great advantage, and, indeed, is absolutely necessary to promote the growth and preserve the health of those who have not the opportunity and inducement to exercise that is afforded in rural life. Most as- suredly the elegance of the female frame will be better attained by walking in the open air, reading their books in the green fields, under some umbrageous shade, riding on horseback and using the cold bath (other circumstances permitting) than by the pernicious habit of confinement all day to the house so frequently indulged in, and afterwards walking out in the night air in thin attire. Exercise, to be beneficial, should be regular, and not exces- sive, and, like bathing, should not be engaged in immediately before or after meals. I need scarcely add that in this climate the mornings and evenings are the most desirable periods dur- ing the warm season, and mid-day in the winter. DIET. The necessity of attention to diet for the preservation of the general health is so obvious as to render superfluous any preli- minary observations for its enforcement, but as many affections of the eyes are produced by improper diet, we shall briefly con- sider the subject. Wholesome and sufficient food, composed of a due admixture of animal and vegetable substances, is the proper subsistence of man; indeed the constituent elements of animal and'vege- 112 PRESERVATION AND IMPROVEMENT OP VISION. table matter are identical. The former contain a larger amomit of the nutritive principle ; the latter take a longer time to di- gest, and are more likely to sour on the stomach. SoHd food is more easily digested than Hquid, and therefore invalids ought to partake sparingly of soups and fluids. The cooking of food is extremely important. Boiled, roasted and broiled, are the most proper modes of cooking for delicate persons, but even these simple cuhnary operations require skill and experience to be executed aright ; to render some articles digestible considerable cooking is necessary, vi^hile a similar pro- ceeding with others would produce the opposite effect. Professor Liebig, of Germany, has recently written a letter to Professor Silliman, a portion of which is taken up with exam- ining the relative advantages of boihng and roasting meat : " The method of roasting is obviously the best to make flesh most nutritious. But it does not follow that boiling is to be interdicted. If a piece of meat be put in cold water, and this heated to boiling, and boiled till it is " done," it will become harder and have less taste than if the same piece had been thrown into water already boiling. In the first case, the mat- ters grateful to the taste and smell go into the extract — the soup ; in the second the albumen of the meat coagulates from the surface inward, and envelopes the interior with a layer which is impregnable to water. In the latter case, the soup will be indifferent, but the meat delicious." As a general rule white and young meats, as lamb, veal, pork and fowl, ought to be well di-essed, while beef, mutton and aqua- tic birds are better underdone. Baking and frying are decidedly the most injurious methods of cooking, as food thus prepared is very indigestible. PRESERVATION AND IMPROVEMENT OF VISION. 113 Our feelings are often the best guide as to what we ought to eat and what abstain from. Many persons have an idiosyn- cracy, or pecuUarity of constitution in respect to food, the sim- plest things as mutton, fish, hone}', (fee, acting on them as poisons, and this is not from caprice or whim on their part. Within the circle of my own acquaintance is a lady, who, having on one occasion partaken freely of oysters, to which she was very partial, was seized with violent and alarming pains in the stomach. The oysters were probably in an unhealthy state for it was then the summer season. This occurred several years ago, and as the taste for oysters still continues she has several tunes ventured to indulge slightly. They have also been dis- guised and given to her, but in either case the result is alike — she is invariably attacked with the most excruciating and di-eadful pains. Some patients require a generous diet : to such, boiled leg of mutton, roast beef, broiled mutton-chop, the back of a rabbit, boiled fowl and chickens, nice sweet-bread and tripe, are most suitable. White fish, and raw oysters, eggs lightly cooked, good dry potatoes, turnips, asparagus and tomatoes, and fresh and ripe fruit, are also appropriate, and for beverage, the pi#e Crotoii, although, in some cases of debility, it becomes necessary to prescribe a little wine, ale, porter, or even weak brandy and water. Good black tea or a limited quantity of coffee, neither too strong, are refreshing and beneficial. Goats and asses milk and butter-milk, also agree well with some valetudinarians. Water, the natural drink of man, next to the air we breathe, is the most essential element of vital existence. It therefore be- comes a matter of the first importance to obtain it of the utmost purity. Rain water procured in the country, free from the con- taminations of large towns, is the purest water, but nevertheless it contains a considerable quantity of carbonate of ammonia. 8 li'l PRESERVATION AND IMPROVEMENT OF VISION. Spring and pump water are impregnated with various saline ingredients Avhich they dissolve in peicolating through the rocks and earth, they are, therefore, not suitable for dyspeptic per- sons. River water is a mixture of rain and spring water, but from whatever source it is derived it always contains more or less decomposed organic matter in suspension or solution which is formed mostly of the exuviae of vegetable and animal substances. By means oi the solar or oxyhydrogen microscope myriads of animalcules can be observed inhabiting the minutest quan- tity of river water. These aquatic animals, as also vegetable parasites, [ciitojjhyta^ and eniozoa.) it is not at all beyond the range of probability to suppose may produce disease in the hu- man system, and various cases have been cited where such apparently was the case. The engraving exhibits a magnified i wm view of some of these little animals. IS'ow by filtration, these as well as all other suspended impurities can be removed, and this is most thoroughly accomplished by Jennison's Diaphragm Filter, a most admirable £,nd excellent contrivance, the result of skill and science and a fresh contributor to human happi- ness and comfort. These filters ou2:ht to be used in everv PRESERVATION AND IMPROVEMENT OF VISION. 116 family where health, cleanliness and purity are really appre- ciated. They can be procured in most of the large cities of the Union, and in this, at 349 Broadway. The invalid must avoid all indigestible food, as salt and smoked meats, salt fish, butter and fatty substances, hot-bread, rich cakes, pastiy, pan-cakes, fried dishes, lobsters, (fcc. The periods for eating ought to be fixed, with an interval of four or five hours between each meal. We should always rest before and after each repast, and retire from the table with some ap- petite still remaining. Most persons have seen the quaint dis- tich of the able but eccentric Abernethy — "If you wish the gourmand's motto to follow, Eat, digest, masticate, and swallow." The state of the bowels and of the digestive system is of the utmost consequence, and demands unremitting and regular attention. The practice of constantly taking medicine to pro- duce order in this respect cannot be too forcibly objected to. An occasional mild aperient may be necessary, but habitual purgatives are destructive to the, well-being of the general econ- omy, nor do they accomplish or induce the desired exactitude ; as after their operation has ceased the bowels become more con- stipated. To effect regularity the great secret is to set apart a precise hour, and never to defer, or allow any interruption to, the methodical daily attention to this point at that particular period. This plan, if perseveringly pursued, will be ultimately crowned with complete success, particularly if attention be paid to diet, and when requisite a proper selection made of such articles as have a laxative tendency — sucli as vegetables and fruits. 116 PRESERVATION AND IMPROVEMENT OF VISION. TOBACCO. The wide spread habit of smoking has not yet had due me- dical attention paid to it and its consequences. The effects pro- duced by the immoderate use of tobacco have been recently so clearly pointed out by the eminent Dr. Laycock, that I cannot, I think, do better than avail myself of his description of them — premising that my own observation fully confirms its justice and accuracy. It is only by two or three years' observation that Dr. Laycock has become fully aware of the great changes induced in the system by the abuse of tobacco, and of the varied and obscure forms of disease to which especially excessive smoking gives origin. Some of these he met with in the pharyngical mucous membrane, the stomach, the lungs, the heart, the brain, and the nervous system. The tobacco consumed by habitual smokers he estimates from half an ounce to twelve ounces per week, the usual quantity from two to three ounces. Inveterate cigar smokers will consume from four to five dozen per week. The first morbid result is an inflammatory condition of the mucous membrane of the lips and tongue ; then the tonsils and pharynx suffer — the mucous membrane becoming dry and con- gested. If the thorax be examined well, it will be found slightly swollen, with congested veins meandering over the surface, and here and there a streak of mucous. Action ascends upwards into the posterior nares, and there is a discharge from the upper part of the pharynx, and irritation is felt w^ithin the anterior nares. PRESERVATION AND IMPROVKMENT OF VISION. 117 The eye htconies affected with heat ; slight redness, lachry- tnatlon, and a pecidiar spasmodic action of the orhicidaris viuscle are experienced, together with intolerance of light on awakening from sleep in the morning. The frontal sinuses do not escape : there is a heavy dull ache in their region. Descending down the ahmentary canal to the stomach, the results, in extreme cases, are symptoms of gastritis. Pain, tenderness, and a constant sensation of sickness and a desire to expectorate, belong to this affection. The action of the heart and lungs is impaired by the influ- ence of the narcotic on the nervous system ; but a morbid state of the larynx, trachea, and lungs results from the direct action of the smoke. The voice is observed to be rendered hoarser, and with a deeper tone. Sometimes a short cough results ; and a case of ulceration of the cartilages of the larynx came under the doctor's notice. The patient was such a slave to the habit that he hardly ever had the pipe out of his mouth. Similar sufferings have been caused by similar practices in other instances. Another form is a slight tickling low down in the pharynx or trachea ; and the patient coughs, or rather hawks up a grumous looking blood. It is so alarming as to be mistaken for pulmo- nary haemoptysis. The action of tobacco smoking on the heart is depressing; and some individuals who feel it in this organ more than others complain of an uneasy sensation about the left nipple — a dis- tressing feeling, not amounting to faintness, but allied to it. The action of the heart is observed to be feeble and irregular. An uneasy feeling is also experienced in or beneath the pectoral muscles, and oftener on the rio^ht side than on the left. 118 PRESERVATIOx\ AKD IMPROVEMENT OF VISION. On the brain the use of tobacco appears to diminish the ra- pidity of cerebral action, and check the flow of ideas through the mind. It differs from opium and henbanCj and rather ex- cites to wakefulness, Kke green tea, than composes to sleep — induces a dreaminess which leaves no impression on the memory, leaving a great susceptibility, indicated by a trembling of the hands and irritabihty of temper. Such are the secondary re- sults of smoking. So are blackness of the teeth and gum- boils : there is also a sallow paleness of the complexion, an ir- resoluteness of disposition, a want of hfe and energy, and, in constant smokers who do not drink, a tendency to pulmonary phthisis. Dr. Wright, of Birmingham, in a communication to the author, fully corroborates these opinions ; and states that smoking hot only is very hurtful to the organs of vision, but produces gastric affections and lowness of spirits ; and, in shorty is very injurious to the respiratory, circulating, alimen- tary and nervous system. EDUCATION, Train up a child in the way he should go and when he is old he will not de- part from it." — Proverbs. This is a very impressive command combined with a solemn assurance of an ultimate reward for the trouble, anxiety and perseverance necessary for the instruction of youlh. But pa- rents and others entrusted with so grave a responsibility as the education of the rising generation ought to know that it is not enough to inculcate sound moral and religious principles in the PRESERVATION AUD IMPROVEMENT OF VISION. 119 Qiiiids of their young charge, or to have them perfected in every grace and accomphshment of modern times ; there is yet another duty to be performed, often too much neglected- -physical edu- cation — for while constant and untiring mental efforts are ever required to furnish and adorn the interior, the substantiality of the structure or tenement where all is to be lodged, meets with but little consideration and less care. Indeed these attainments are sometimes purchased by a dreadful sacrifice. All this might be amended or prevented by a happy combination of mental and physical education. I do not for a moment under-estimate the value of parental and early mental culture, and the advantage of training up children to habits pf obedience and industry, for I recollect the terrible judgment attendant on disobedient and undutiful chil- dren, according to that awful scriptural denunciation — "The Eye that mocketh at his father and despiseth to obey his mother, the ravens of the valley shall pick it out and the young eagles shall eat it." But I would endeavor to impress upon the mind of the reader that the severe studies in some schools are indeed tasks whereas, they should be regulated in proportion to the tender age and strength of constitution of each pupil. Early over-application to books has caused in many persons obscurity of vision and even entire blindness, rendering the balance of their days miser- able and unhappy. This early over-use of the organs of vision before the system is perfected is one reason why so many stu- dents and young persons among the wealthier classes are short- sighted and compelled to wear glasses. Indeed many a student would be relieved from the lassitude which he feels while pour- ing over his books, would he but give a portion of his precious time to the improvement of his health, and if he cannot be persuaded to do this he will prove to his sorrow that " much study is a weariness to the flesh." 120 PRESERVATION AND IMPROVEMENT OP VISION. Childhood is the period of exuberant and indeed vehement activity, and nature requires almost unhmited and constant exercise. If at this youthful and joyous period of existence we prohibit the full and free enjoyment of muscular exertion we are acting contrary to the dictates of nature and this we can- not do with impunity. 1 have elsewhere alluded to the various kinds of exercise ; of course, in selecting the mode of exercise proper for either sex, nature and our own sense of propriety must be our guide. — though both "Not equal, as their sex not equal seemed, For contemplation he, and valor formed; For softness she, and sweet attractive grace.^ HOUSES, OFFICES AND MANUFACTORIES. When we have an opportunity of making a selection, a dry elevated location, surrounded by a free circulation of air ought always to be chosen, and in cities the sunny side of the street is the healthiest. Marshy situations are detrimental to vision, and where necessity compels a residence in such vicinage it were prudent to occupy a position as much to windward as possible. The rooms should be lofty and well lighted, not in the modern style with windows down to the floor. However novel and elegant this may appear, it is not an improvement on the good old plan of our ancestors, for through such windows the light is reflected from below, and all objects are consequently viewed in a false light. PRESERVATION AND IMPROVEMENT OF VISION. 121 The light should shine directly on the windows, and not be reflected from some opposite wall or building', particularly if these should be painted white, or white-washed. 1 have fre- quently remarked with surprise, that many merchants and others who reside in princely palaces up town immure them- selves for perhaps twelve hours a day, or one half their natural lives, '• cabined, cribbed, confined," in close back offices totally dependant on the reflection from their neighbour's whitened wall for the highly detrimental and limited supply of light which they receive. Nothing can be more trying or injurious to weak eyes. Sleeping apartments and manufactories, where a number of persons congregate, ought to be very freely ventilated. Few things contribute more towards healthy strong eyes than plenty of fresh air, while many diseases are engendered by an impure atmosphere: the offensive exhalations from our proverbially dirty streets are a potent and frequent cause of disorders of the eye. The light should be so admitted into the rooms as to be as regular as possible. When it is too glaring a blue or green window shade will be of great advantage. The window shade, or curtain, ought to be arranged so as not to blwv backwards and forwards, for such vacillation is constantly exposing the eyes to sudden changes of light. The walls and furniture of the rooms ought not to be of a bright dazzhng color. Too much gilding is also very trying to delicate eyes. The position of the bed in our sleeping apartment is an ob- ject of some importance : it should not be placed opposite to the rising sun, for this situation would expose us to a strong and sudden light on first awaking in the morning. 122 PRESERVATION AND IMPROVEMENT OF VISION. It would be very desirable if the room occupied in manufac- tories, or elsewhere, where persons are engaged in minute and fatiguing work, had a good perspective or view from the window, for great relief would be experienced in occasional cessation * from work, when the eyes felt weary and clouded, by looking out at distant objects. This is the natural relaxation of the eyes. How beautifully the wisdom and forethought of a kind Pro- vidence is illustrated by the pervading colors of nature — the green grass and the soft blue firmament present the colors the coolest and most refreshing to the eye. From the cradle to the grave the eyes are used unsparingly, and scarcely is the tiny tenant of the former rocked to slumber ere it is startled from its short repose and its little eyes are ex- posed to a painful and dangerous ordeal, for no practice is more common than that of taking a new-born babe to the bright glare of the sun or a lamp, to exhibit the little stranger to every new visitor. It cries from the pain caused by the light acting on its tender retina. The little "deary" is hushed up, its feeble screams of agony are attributed to any thing but the true cause, and the same ceremony is repeated over and over again — resulting, unhappily but too often, in weakened or dis- eased vision. But the injurious effects of a sudden transition from gloom to bright light, are by no means confined to infancy. We all have felt pain and uneasy sensations on suddenly going out into the bright sunshine from a dark room, or on candles being introduced into the apartment where we have been sitting for some time without light. A memorable instance of the effects of such sudden change occurred at the demolition of the French Bastille. On the day on which the head of Robespierre rolled on the scaffold, the Parisian people, frantic with joy, burst in the gates of that PRESERVATION AND IMPROVEMENT OP VISION. 123 infernal prison, and gave freedom to the captives who had so long pined within its dismal walls. These, delirious with de- light, rushed through the doors, slippery with the blood of so many of tlieir ill-fated companions. But their eyes so long accustomed to the deep gloom of the dungeon, w^ere unable to bear the sudden flood of light poured in upon them by the burning beams of a summer sun ; and many amongst them only exchanged one sad calamity for another — the darkness of the prison for that of perpetual blindness. The destructive effect of a sudden influx of hght has some- times, with wicked ingenuity, been made the instrument of in- flicting the keenest torture, for " man's inhumanity to man," has ever been a stain upon our common nature. Dionysius, the tyrant of Syracuse, used to confine his unhappy victims in dun- geons of the deepest darkness, from which they were violently thrust into a chamber, illuminated with the most intense glare of light. The poor wretches, after enduring the most excru- ciating agony, were thus quickly deprived of sight. Every student of ancient history is familiar with the ciuel revenge inflicted by the Carthaginians on Regulus the Roman Consul and General, when they had at length made him pri soner after they had endured a series of disastrous defeats on many a battle field over which the Roman Eagles had remained floating in triumph. They shut him up in a dark prison, and then, with barbarous cruelty, having cut off* his eyeUds, they exposed him to the fierce rays of a burning sun. In a short time the visual orb was extinguished for ever. 124 PRESERVATION AND IMPROVEMENT OF VISION. ARTIFICIAL LIGHT. Artificial light is much more injurious and irritating to the eyes than the pure hght of day, because the red and yellow rays preponderate over the blue ; consequently if we direct our eyes to a book or sheet of paper, we perceive it appears of a yellowish or reddish tinge instead of white as in the day time ; the contmst between the letters and the paper is not so marked, the letters are not so accurately defined, and a greater effort of the eyes becomes requisite. The increased heat from artificial light irritates the eyes and causes chronic inflammation of the lids and a diseased s-tate of the secretions. Where many lights are used the air of the room becomes parched, dry and hurtful to the eyes, producing itchi- ness and stiffness of the lids. The great desideratum in artificial Hght is to have it as re- gular and steady as possible. The qualities most desirable in a good lamp are, that the light should be pure, sufficient, unwavering, and equally diffused and unaccompanied by smell or smoke. To attain these ends it is necessary that the oil should be of a proper fluidity and be constantly elevated to the point of combustion. In the ordinary lairips, as the astral and solar, PRESERVATION AND IMPROVEMENT OP VISION. 125 the light diminishes as the oil becomes lessened in the reseiToir. The viscidity and consequent sluggish supply of oil to the wicks is a great obstacle to the combustion of lamps, " an obstacle nearly insuperable with lamps of the common construction dur- ing the winter months." The admission of an adequate supply of atmospheric air to the flame is also essential, as otherwise the light will be insufficient, or the lamp will smoke on the wick being elevated. Among the vast number of lamps that have been constiiicted I cannot find one that combines these desiderata, or indeed that is free from objection. Dr. Ure says the Mechanical or Carcel Lamp does not possess the necessary attributes, for the oil being pumped up through tubes by clock work to the wick " prevent3 perfect uniformity since it fluctuates a little, but always percep- tibly to a nice observer with the alternate action of the pump work becoming dimmer after each successive jet of oil and brighter just before its return. The flame, moreover, always flickers more or less, owing to the powerful draught and rectan- gular reverberatory shoulder of the chimney," and he concludes by remarking that " they can hardly be trusted in the hands of a servant, and when they get at all deranged they must be sent to their constructor to be repaired." The next lamp that deserves attention is Parker's Hot-Oil liamp. By means of this contrivance the viscidity of the oil is overcome and from the position of the reservoir being above the wick a constant supply of oil is secured at the proper elevation without the necessity of any comphcated mechanism. The highly scientific author from whom I have before quoted, says that " the Hot-Oil Lamp burns with a much steadier flame than the Mechanical ;" and he ascertained that its relative illumina- tion, when compared with the Mechanical Lamp was 121 to 100, while the French Annular Lamp was found to reach only .50. Notwithstanding all this I must say that I do not consi- 126 PRESERVATION AND IMPROVEMENT OP VISION. der Parker's Lamp by any means perfect. The following table is the result of Dr. Ure's investigations : Cost per hour of 100 Illumination. Pence. Mechanical or Carcel Lamp, with sperm oil, ------U Parker's Hot-Oil Lamp, do. do. do. 1 French Lamp, do. do. do. ------ IJ Wax candles, 6 Spermaceti candles, --------------- 5i Tallow candles, --.- 2i Lamps possess an advantage over candles, inasmuch as we can increase or diminish the light as is most desirable. Wax or good spermaceti candles produce a very excellent light, but two or more should invariably be used, when reading or working. Dr. Ure says, " after comparing lights of many kinds, I have every reason to conclude that a large wax candle of three to the pound, either long or short, that is either 12 or 15 inches in length, as manufactured by one of the great w^ax chandlers in London, and furnished with a wick containing 27 or 28 threads of the best Turkey cotton, is capable of furnishing a most uni- form or nearly invariable standard of illumination." And he adds that it is very remarkable that whether they were three's, four's, or six's in the pound, each afforded very nearly the same quantity of light, for each required to be placed at a distance of three feet from the screea to afford a shadow of the same tint as that dropped from the Mechanical Lamp estimated at 100. Artificial light is a highly interesting and important matter, especially to persons with tender eyes who are compelled by necessity, or who from inclination devote many hours every night to reading, writing, sewing, or minute work of any de- scription. Such persons very frequently, and, indeed, justly PRESERVATION AND IMPROVEMENT OF VISION. 127 attribute various distressing sensations and diseases of the eyes to improper or unsuitable light. The subject of illumination has occupied my attention for some time, and I am at present engaged in making a series of experiments. The result of my investigations I hope at no distant period to be enabled to pre- sent to the public in some useful form. Candles or lamps should not be placed before the eyes ; the light should not fall perpendicularly or horizontally on the sight but obhquely, and if there are two or more lights in a room they should be of the same height. The injurious effects of artificial light may in some degree be prevented by protecting the eyes from the direct action of the light, by having a shade over the lamp. This shade, or reflector, ought to be made of tin or brass, bronzed on the out- side, and painted with ultra-marine of a light blue color on the inside. The inner surface should be smooth and even, and destitute of polish, or shining properties. Light that is thrown from such a shade on a book or paper, will cause it to appear whiter and the letters more distinct, and the light will be re- freshing and cooling to the eyes. If a proper lamp, so arranged, be suspended in the centre of a room where a number of persons are w^orking around a table, there will be sufficient illumination for the minutest work. Shades for lamps or candles, may be also made of paste- board, the inside colored as above, and the outside of a gray or neutral tint. Light blue glass chimneys are very useful, as they give the light a soft pleasant hue. Plain ground glass shades soften and diffuse the light, but those that are cut are highly objectionable. 128 PRESERVATION AND IMPROVEMENT OF VISION. Some artizans use a glass globe, filled with water, to concen- trate the light on their work. This contrivance is not to be recommended ; but if a small quantity of ammoniated copper is added to the water, say sufficient to throw a sky blue color on a sheet of paper held behind the bottle^n the day time, it will be found to render the light purer and more refreshing. Carbonic acid gas, which is produced by respiration and during combustion, is a strong narcotic and destructive to life. It is computed that when an apartment containing a number of persons is illuminated to the ordinary extent, four times as many cubic feet of fresh atmospheric air a minute, as there are persons in the room, are requisite. When the carbonic acid gas, which is generated by respira- tion and the lights, is conveyed away, and a fresh supply of air freely supplied, no injury ensues ; but crowded rooms, with numerous hghts, and badly ventilated, are very pernicious, causing headaches, distempered eyes, and general injury to body and mind. Compositors, particularly those engaged on morning papers, suffer more from these causes than any other w^orkmen. There- fore, in addition to the rooms being well ventilated, the lamp ought always to have a tube with a funnel-shaped moutJi hung over it, and this tube or pipe should be continued out through the roof, or into the chimney, to carry away the foul air. It is to be regretted that a little more attention is not paid to the position of the lights in our Lyceums, Lecture-rooms, and other Public buildings. The mind is so entertained by the pro- ceedings of the evening, that it pays but litlle heed to the occa- sional hints that the eyes give of the discomfort to which they are subjected by being exposed to the bright glare of a lamp or gas-burner, and the consequence not unfrequently is that these PRESERVATION AND IMPROVEMENT OF VISION. 129 do not recover for several days from the irritation thus produced. The hghts ought to be of greater power than they usually are, and suspended in a more elevated situation. This arrange- ment of them would not only very much relieve the eyes, but improve the atmosphere of the building, for much of the impure and vitiated air being above the level of the lights, would thus escape upwards w^ithout offending the lungs of those sitting be- low, and in this way, not alone the eyes, but the respiratory organs also would be saved from much, and, sometimes, irre- parable injury GENERAL OBSERVATIONS. Many persons have a habit of rubbing their eyes in the morning to remove, as it is expressed, the " sleep " from them. This is a very pernicious custom. The undue presstire on the eyes is highly injurious, and consideiable irritation is constantly produced by the eye-lashes being forced into the eyes. It is much more proper, and certainly more luxurious, to bathe the eyes with a little cold water, or if the secretions have become hardened at the root of the eye-lashes, tepid water may be sub- stituted. Bathing the eyes two or three times a day, particularly in dusty weather, or whenever they feel heavy or fatigued by close application, is salutary and beneficial, and very invigorat- ing to the vision. This, however, should never be performed while in a state of free perspiration. The jet, or Douche Bath, is exceedingly appropriate and sometimes of incalculable advantage in those cases termed 9 130 PRESERVATION A.ND IMPROVEMENT OF VISION. " weakness of sight," and also in a great variety of other affec- tions arising from debility or want of energy in the nervous structure of the eyes. Cologne water, or other spirituous applications to the temples, once or twice a day, may be used as additional auxiharies for restoring the tone of the eyes. It is exceedingly important to guard the eyes against expo- sure to the injurious effects of briUiant and reflected light. The most disastrous consequences may result from the neglect of this precaution ; and so well has this been taught by experience to even the unlettered savage, that he has invented a sort of snow spectacles, or snow eyes^ " yeiix a la niege^'^ as they are called by the French settlers near the Esquimaux of Hudson's Bay, to preserve the eyes from the dreaded effects produced by the intense reflexion of the sun's rays. The most dreadful sufferings, and, in numerous instances, a total loss of vision, have been endured by whole armies in marching through the parched and sandy deserts of the East, where — "Vertical the sun, Darts on the head direct his forceful rays : In vain the sight dejected to the ground Stoops for relief; thence hot ascending streams, And keen reflection pain !" — Thmnpson. The celebrated Greek historian Xenophon, mentions, in that admirable and graphic work, the "Cyropedia." that on one occasion the army of Cyrus marching for several days through mountains covered with snow, the dazzling splendor of its whiteness prejudiced the sight of many of his soldiers and blinded some of them. We ought to avoid exposing the eyes to smoke or to high PRESERVATION AND IMPROVEMENT OF VISION. ISi' wind ; and, wlien we can conveniently do so, we should keep within doors when the dust is blowing about. We must not tax the eyes too much, even although they may seem to be in a sound state, if we are desirous of possessing vision intact to a good old age. Continued reading of bad print severely tries the eyes, as does the pernicious custom of reading by twilight or by the light of the fire. Newspapers require to be well aired or dried before venturing on their perusal. Students and literary persons will find it a great advantage to vary their position while pursuing their studies, by sometimes standing at an elevated desk, thereby avoiding the constant stooping of the head. Another golden rule for their observa- tion is never to go to bed with cold feet. Young persons, of delicate sight, ought to select an occu- pation, or business, that does not require a close appHcation of the eyes ; but persons with impaired vision, who are advanced in life, and who are dependant solely on their labour for a sub- sistence for themselves, and perhaps their families, are, indeed greatly to be commisserated if their employment is of that minute nature which is so injurious to the sight. Book-keepers, compositors, engravers, watchmakers, tailors, and shoemakers, are the persons that most frequently suffer, and especially our poor industrious sempstresses and tailoresses, who toil from morning to night, and, oftentimes, through the long and tedious hours of the night to obtain a scanty and precarious livelihood. It is necessary to be very prudent and cautious under such circumstances, especially if it be observed that the eyes can no longer see at the distance they were accustomed to, that they feel hot, dull, heavy or painful after close application, which is f 132 PRESERVATION AND IMPROVEMENT OF VISION. relieved by a cessation from employment ; or if they present a red, weakened or watery appearance, or that the other premon- itory symptoms are present, enumerated in our description of that afflicting disease Amaurosis, which is so feehngly pour- • trayed by the suffering Milton, — " These eyes, though clear To outward view, of blemish, or of spot, Bereft of light, their seeing have forgot ; Nor to the idle orbs doth sight appear Of sun, or moon, or star throughout the year ! Or man, or woman !" Many of the foregoing suggestions will, if adopted, be found beneficial to persons who are forewarned by any of the symp- toms above described. I would, in addition, advise them to vary their work as much as possible, ajid, if practicable, to work only by day-light ; or, at least, to select the most difficult work for the day time, deferring the easier part for night-work. Stopping for even a short interval to rest the eye§, and bathing them in cold water, will be found refreshing, as well as walking outside the building for a few minutes, or looking out of the window. Immediate application to business on first rising in the morning, or too soon after meals, ought to be avoided. A flat open vessel, containing water, and placed in a hot room, particularly if it be heated by a stove or anthracite coal, will, from its constant evaporation, in some degree prevent the air from becoming dry and parched ; and persons working close to a strong light, will find that if they lay a wet sponge near them it will sensibly moisten and cool the air, and thus, to some extent, reHeve the eyes from its hurtful effects. In several instances of affections of the nervous structure of the eye, I have found the electro-magnetic battery, judiciously applied, a powerful auxiliary in their treatment. It requires however the exercise of some skill in its apphcation. PRESERVATION AND IMPROVEMENT OF VISION. 133 The Magneto-Electrical Instruments manufactured for this purpose by B. Pike & Sons, 166 Broadway, are decidedly supe- rior to all others tliat I have examined. Whenever any trifling- affection of the eye occurs, there is usually an immediate resort to the use of shades^ and this, though very often highly pernicious, the oculist finds some difficulty in preventing, as the opinioi: of their usefulness and necessity is strongly rooted and universal. They are really requisite where there is great intolerance of light, but in slight complaints they are very injurious. Case. — On a recent occasion, a celebrated Comedian called at my office. He had on the usual green shade, his eyes were a little heated and tender, and suffused with tears. On enter- ing, he exclaimed, his countenance assuming a peculiarly arch and expressive look, " Forgive the gushing tear ! Alas ! I feel I am no actor here." After this somewhat ludicrous prologue, I made an exam- ination, and perceiving that his ailment was very trifling, 1 recommended him to bathe his eyes with rose-water and to dispense with his shade. He followed my advice, and the ten- derness and lachrymation speedily disappeared. Shades are sometimes necessary when the light is very pain- ful to the eyes, but in slight attacks they are worse than use- less, as they prevent a free circulation of air around the eyes, keep up the heat and inflammation, and exclude the light which is the natural stimulus of the eyes. Where they are worn they should be very light, and not press tightly or heavily on the eye or brow. The color of the silk with which they are covered should be either blue or green. 134 PRESERVATION AND IMPROVEMENT OF VISION. The influence of the mind on the eye and its affections^ is highly important, and deserves serious attention. Immoderate excess of any of the passions, unnatural commotions of the mind, anger, rage, and such like, are exceedingly detrimental to the visual faculties. Yiolent temper must therefore be con- trolled, undue excitability subdued, and abstinence from other vicious habits inculcated. The depressing passions, or those that lower the animal and vital powers, especially giief, have a direct tendency to weaken or even destroy sight. Many sad and touching instances of total blindness from excessive sorrow have occurred, where the unhappy and deeply afflicted sufferer " opened the flood-gates of the heart," and " would not be comforted," but was " like Niobe, all tears." The salutary effects resulting from a serene and tranquil mind, are felt in no part of the system more beneficially than in the eye, allaying its tendency to irritability, and adding to it renewed tone and vigor. It is therefore exceedingly desirable to promote this happy condition of the mind by cheerful com- pany, agreeable society, and occasional indulgence in harmless and innocent amusement or I'ecreation. Many of the rules that I have urged as essential for the pre- servation of the eyes, are every day violated by the unthinking with apparent impunity ; but although the eyes may for a long time resist these deleterious practices or influences, yet sooner or later must the penalty be paid, for ultimate, if not present suffering will be the inevitable result. NEAR SIGHT AND FAR SIGHT. 135 NEAR SIGHT AND FAR SIGHT. I have elsewhere alluded to what is termed " Asthenopia," (from a priv. sOsvos, strength, and on-?, the eye) or " weakness of the sight," and the proper course to be pursued under the ex- istence of such a condition of the eyes. Before, however, entering on the subject of near sight and far sight, I may mention that there is a peculiar state of the eye called "Day-blindness," or, as it is technically termed, Hemeralopia, from ^t^a, day, a priv. and Sipis, vision. Where this exists the individual can only see imperfectly during the day, but in the evening vision is greatly improved. This affec- tion seems to arise from a particular sensibility of the retina to light. The Albino labors to some extent under this disad- vantage. There is another affection, Nyctalopia, (from vv^, nighty a priv. and Sipi(r, vision,) or " nighc-blindness," wherein the per- son can see with distinctness during the day but cannot dis- tinguish objects in the evening or at night, this being exactly 136 SHORT SIGHTEDNESS. the reverse of the former affection. I had recently a patient, a coloured man, a native of Cuba, who laboured under this defect from his childhood. He was a tailor, and could see dis- tinctly to work in the day-time although he held objects closer to his eyes than is usual, but he could not see at ail at night. After some preparatory treatment I provided him with concave glasses, and by their aid, to his great satisfaction, he was enabled to walk about the streets in the evening, as he could discern sufficiently well to avoid coming in contact with the passers-by. SHORT SIGHTEDNESS. Myopia, so called from the Greek words /^vw, I shut, and &>?//, the eye, because when short-sighted persons look at distant ob- jects they half close the eye-hds. If a person cannot see to read with distinctness and ease common-sized print at a distance of about twelve inches, he may be said to be myopic or short-sight- ed. If, on the other hand, the point of distinct vision is at a greater distance than fifteen inches, he is said to be presbyopic or far sighted. Perfect vision ranges from nine to fifteen inches. If it is below nine or above fifteen inches it may be distinct but it is not perfect. Near sight is almost exclusively confined to young persons, but not invariably, as aged persons are some- times near-sighted. It is generally first observed about the age of puberty, when steady application of the eyes is required for study or any minute occupation, and this is the reason why so many young persons devoted to literary pursuits are short-sight- ed. The individual remarks that he cannot see so well as his companions or acquaintances, cannot distinguish his friends at a little distance, nor read the names of streets or sign-boards without approaching close to them, and when reading he must SHORT SIGHTEDNESS. 137 bring the book closer to his eyes than the generality of persons do. If he puts on a pair of concave glasses he is quite astonish- ed and pleased to find that he can see with the utmost clearness objects which were before undistinguishable at the same distance. Myopia gradually increases if too close application of the eyes is made to minute objects. It has been caused suddenly in some instances by exposure to cold or damp. It is, however, generally caused by some peculiar mechanical conformation of the eye, or by too great a density of the refractive media. The cornea or the crystalline lens is too convex, or the distance be- tween either of these parts and the retina is too great, or their refractive density is too powerful, or the adjusting powxr may be disarranged. Yf e noticed before, when speaking of the forma- tion of images, that the rays of light flowing from the object at which we look are brought to an exact focus on the retina, and consequently the image is depicted there. We also ascertained in examining the properties of convex lenses that the greater the convexity the greater is the refractive power, so that if any of the causes which I have just now enumerated exists, the rays of light proceeding from the object are too powerfully refracted, and unite in a focus before they arrive at the retina, as exhibited in the annexed diagram. Although the focal point of the rays does not reach the retina but is anterior to it. nevertheless some sensation is produced, be- ing a kind of indistinct vision, and this is caused by the rays 138 SHORT sightiI'dness. crossing one another at their focai point and proceeding on to the retina where they form a faint and confused impression. Near-sighted persons are observed generally to have promi- nent eyes. The cornea is convex, the anterior chamber deep, the pupil large, and the entire eye firm to the touch ; sometimes, however, there is no peculiarity noticeable, as the difficulty may be in the interior of the eye. Near-sighted persons see with great distinctness when they bring the object close to their eyes. This is owing to their see- ing the object under a greater angle than other persons ; that is to say, the extreme rays, and indeed all the others become divergent, owing to the before-mentioned causes ; this can be seen in the following cut — e A. represents the eye, and the object b. c. seen at m, and also at n. double the distance will of course appear under different angles to the eye. for b. A. c. is larger than d. A. e. and will include it, so that to bring an object close to the eye has the effect of magnifying it, or of causmg the rays to diverge, that is though b. c. and d. e. are of the same lengths, yet b. c. being nearer the eye will appear the largest. Near-sighted persons see small objects more distinctly than other persons, because they view them under a larger visual angle as we have just seen. They also see them with a weaker light, because the object being closer to the eye, a greater num- ber of rays proceeding from it arrives at the eye. They also see better and a httle further off by a bright than FAR SIGHTEDNESS. 139 by a moderate light, because the pupil is contracted by the strong light and consequently the circumferential rays, or all but the more central and direct ones, are excluded, and for this reason if they look through a small hole in a card they can see at some distance. It is on the same principle they close the eye-lids when trying to view distant objects. Fortunately for mankind art offers means for overcoming the inconveniences of short-sightedness. These, however, we will postpone speaking of until we- have considered the opposite state of the eye, viz. far-sightedness. PRESBYOPIA. From npsaPva-, old, and wj//, the eye. Far-sightedness — so called, because it is a concomitant symp- tom of advanced age ; but as Myopic eyes are not in every case confined to young persons, so also Presbyopic eyes are not the attribute of advanced age solely, for they are met with occa- sionally in early life. In most persons, however, the refractive power of the eyes begins to diminish at about forty years of age, and continues to decrease as they become more advanced. In fact, Presbyopia may be considered a natural change. Persons are said to be presbyopic when they are compelled to hold a book at a distance of two feet or upwards from them when reading, although they had formerly been able to read at a distance of from nine to fifteen inches. Those who are so situated find it difficult to execute any minute work, such as to mend a pen or thread a needle. When persons become far- sighted the eyes do not appear so prominent as they did previ- ously. The cornea or the lens is flatter than formerly, or the distance between these structures and the retina is too short. 140 FAR SIGHTEDNESS. and the adjusting power of the eye is generally more or less impaired. The effect produced in either of these cases is to prevent the rays of iight flowing from the object from being converged or brought to a focus, until they pass beyond the retina, as is shown in the figure. Presbyopic, eyes have generally a sunken appearance. The cornea is flat and small, and the pupil contracted ; and in el- derly persons an opaque ring or circle is observed around the margin of the cornea, — the arcus senilis^ or ring of age. Par- sighted persons see a distant object distinctly, because the rays that flow from it are not as divergent as those from near objects, and consequently come more speedily to a focus. Therefore it is that persons with this condition of eye hold a book at arm's length when reading it, inasmuch as the rays that proceed from it require less refractive power to bring them to a focus at the retina. Aged persons cannot see minute objects clearly at any dis- tance, because when they are near they are not within the focus of the eye, and when distant they are seen at a small visual angle, and with little light ; therefore aged persons in addition to holding the book at a distance from them when reading are accustomed also if it be at night to place the candle before them and near the book, and thus by throwing an increased amount of light on the page they can read with more facility. FAR SIGHTEDNESS. 141 The eye in its natural state is, as we have before observed, adjusted to distant objects, and it requires an effort to view near ones. This exertion, if long continued, becomeswery fatiguing and indeed painful, and causes considerable uneasiness in the l)rows and temples. This is more particularly the case with presbyopic persons, for the refractive power of their eyes being lessened, their sensibility impaired, and the adjusting apparatus become rigid by age, an extraordinary exertion and continued t