1^... 
 
f 
 
jjiCONOMY OF THE EYES i 
 PRECEPTS 
 
 FOR 
 
 THE IMPROVEMENT AND PRESERVATIOJ)f 
 
 OF 
 
 THE SIGHT. 
 
 PLAIN RULES WHICH WILL ENABLE ALL TO JUDGE 
 EXACTLY WHEN, AND WHAT 
 
 SPECTACLES 
 
 ARE BEST CALCULATED FOR THEIR EYES; 
 OBSERVATIONS 
 
 ON 
 
 OPERA GLASSES AND THEATRES, 
 
 AND AN ACCOUNT OE 
 
 FOR DOUBLE STARS, AND DAY TELESCOPES, 
 
 '* Qui Visum, Vitam dat." 
 
 By WILLIAM KITCHINER, M.D. 
 
 Author of The Cook's Oracle ; T^he Art of Irivigomting and Prolonging 
 
 Life ; The Pleasure of Making a Will ; Observations on Singing, 
 
 &e. &c,; and Editor of The Loyal, Nationalj 
 
 and Sea Songs of England. 
 
 BOSTON : 
 
 WfJjhS A^n LII.lt— AND E. LITTELL, FHILADELPHIA.. 
 
 1824. 
 
^ ^^ 
 
 CONTENTS. 
 
 PAGE 
 Prefacf, to be read ajttr the Work , • . 1 
 
 Introduction ...•••• 2 
 
 Spectacles for the poor 9 
 
 Chap. 1. On Reading Glasses for Persons 
 WHOSE Eves are impaired by Age; and 
 Single Eye Glasses for the Shurt-sight- 
 ED 10 
 
 II. Spectacles with Plain Glasses . . 16 
 
 III. Cases of Persons who could not read 
 
 IS Spectacles .... 18 and 31 
 
 IV. Hand Spectacles . « . . 14 and 19 
 
 V. Symptoms of the Eyes REauiRiNG Specta- 
 cles to READ WITH 21 
 
 VI. Of Preservers 27 
 
 VII. Table of tle Focal Length of the 
 Magnifying Glasses REauiRED at vari- 
 ous Ages 30 
 
 The time that the First Glasses of 36 Inches fo- 
 cus will assist the Si ^ht sufficiently . .33 
 
 VIII. When to change the First Specta- 
 cles o 34 
 
 The Premature Use of Spectacles, how perni- 
 cious to the Sight ..... 29 
 
 IX. My Grandmother s Spectacles . . 36 
 Spectacles for Gourmands . . , .37 
 
 X. Hints to Persons choosing Spectacles 40 
 
 Divided Spectacle Glasses . . . .44 
 Plan for Preserving the Sight , . .46 
 
 XL Hints to Persons beginning to wear 
 Spectacles : and of Reading-lamps and 
 
3V CONTEHTS. 
 
 Candlesticks . . . . . . • 52 
 
 Case of Dimness of Sight from Over-exercise 
 
 of the Eye 59 
 
 Of the Pole Star « 61 
 
 Of the Double Ring of Satur7i . . .62 
 Contents of the Second Part of the Economy 
 
 of the Eyes 65 
 
 Magnifiers for Artists , , . , ,67 
 Concaves for reducing Miniatures . • ,70 
 Nervous Dimness of Sight . • , .71 
 Ointment for the Eye-lids . . . » 72 
 Chap. XII. Precepts for improving and 
 
 Preserving the Si^ht .... 73 
 The Circumspector ... 75 and 181 
 Sight-Strengtheners for Painters, &;c. ♦ . 77 
 Double Rising Desk . . . , * 79 
 
 Reading Candlestick 81 
 
 Green ©r Coloured Glasses . , . .82 
 To keep Glasses perfectly clean . . .84 
 
 XIII. Glasses for Short-sighted Persons 85 
 History of the Author's Case of Spectacles . 86 
 Invisible Opera Glasses . , . . .93 
 The Disadvantages and the Advantages of be- 
 ing Short-sighted . , . . • 94 
 
 XIV. 'Spectacle Frames . . . .96 
 
 Silver Frames , 96 
 
 Tortoise-shell Do .96 
 
 Blued Steel Do 97 
 
 The Length of the Bridge . . . .98 
 Mean Distance between the Eyes . . .98 
 Width of a common Spectacle Frame . . 99 
 How many Tears shed Daily . . . 100 
 
 Proper Shape for the Openings which hold 
 
 the Glasses ...... 101 
 
 Length of the First Joint . . . .102 
 
 Prices of Spectacles ..... 103 
 
 XV.-. Of THE aiTALITYOF SPECTACLE GLASS- 
 es, and how to measure their focal 
 Length , , , ^ , * 103 
 
 XVI. Pebbles ....... 106 
 
CONTENTS. 
 
 The expense of the Best Glasses is a Groat per 
 Annum . . . • • 
 
 THE 
 
 per fee 
 
 Chap. XVII. On the various Degrees of 
 Perfection of the Eye and ear 
 
 The Gritty Chord 
 
 The Ocular Harpsichord 
 
 Beef and Cabbage, the music of 
 
 Good Sense and Good Senses 
 
 Perfect Senses . . , . 
 
 Bad Senses 
 
 Advantages of Insensibility 
 
 Pancratic Eye-tube 
 
 Portraits of 7)ow6/e »S7ar5 
 
 Dat Telescopes, how to use with 
 Vision and with effective Power 
 
 fit Geminorwn seen double , • 
 
 f Bootis do , , . 
 
 Hints to Observers of Double Stars . 
 
 Hints to Dumpy Fanciers 
 
 Newtonian Diagonal Eye-piece 
 
 Advice to Buyers of Telescopes 
 XVIII. Opera Glasses 
 
 How to adjust an Opera Glass for various Eyes, 
 and for various Ages, and Objects at diffe- 
 rent distances 
 
 How to hold an Opera Glass 
 
 Field of View in an Opera Glass 
 
 The Grand Dandy Opera Glass 
 
 The Stops .... 
 
 The Opening ©f the Pupil 
 
 Revolving Eye-head 
 
 French Operas 
 
 English do • . . . 
 
 Magnifying Power, how to vary 
 
 To see if any of the Object Glass is cut ofF 
 
 Diameter of Eye-glass 
 Do. Eye-head 
 
 Average Distance the common Eye can see 
 distinctly the Expression of the Countenance 161 
 
 109 
 
 109 
 110 
 110 
 112 
 113 
 115 
 116 
 117 
 118 
 121 
 
 124 
 125 
 125 
 126 
 128 
 133 
 143 
 146 
 
 148 
 140 
 152 
 152 
 153 
 156 
 157 
 157 
 158 
 158 
 159 
 160 
 161 
 
Average Distance between Spectators and Per- 
 formers , , , Igl 
 
 Requisite Magnifying Power to enable a Person 
 to see as distinctly as if they were within 15 
 feet of the Stage •«,,., 1612 
 The Bell Opera with one sliding Tube the best 162 
 Of Operas which have many Tubes , . 162 
 Operas for the extremely Short-sighted . . 164 
 Operas that have no focus , . • • 164 
 Invisible Opera Glasses ... 93 and 165 
 Opera for a Picture Gallery c . . . 166 
 Opera for sweeping for a Comet » , , 166 
 The Ouranoiogia ..,,.. 16G 
 Binocular Opera , , , , , .167 
 
 Single Object Glasses 168 
 
 Concave Eye-glasses for varying the Magnify- 
 ing Power ....»., 169 
 To ascertain the relative Powers of Eye- 
 
 Glasses 169 
 
 Imperfections in Opera Glasses^ to discover , 171 
 Prices of Opera Glasses „ • « . . 171 
 Cautions in trying Opera Glasses . . . 172 
 Comparisons of Single and Double Object 
 
 Glasses ,...,., 174 
 
 To measure the Magnifying Powers . . 178 
 
 Diagonal Opera Glass <,<,... 181 
 
 Circumspector . , o . 75 and 181 
 
 Chap. XIX. Theatres ...... 183 
 
 Distance from the Curtain to the Boxes at the 
 English Opera House ..... 184 
 
 Ditto at Drury Lane . • , . .184 
 Ditto at Covent Garden ..... 184 
 
 Of the Extension of the Voice • • , 18^ 
 Mr. Arnold's Theatre . . . . ,188 
 
 Mr. Garrick's , 18§ 
 
 Account of the Expense of Building the present 
 Drury Lane Theatre .... 189—191 
 
 Humber of Seats, &c. in the English Opera 
 House . . . . . . . .190 
 
 pittOj Drury Lane . . -> « a c 192 
 
CONTENTS. Vn 
 
 Number of Seats, &c. in Covent Garden . 192 
 
 Ditto, Haymarket 192 
 
 God I save the King 193 
 
 Ditto, the Words marked as they ou^ht to be 
 sung 198 
 
 APPENDIX, 
 
 RESPECTING SPECTACXES. 
 
 No, I. Rules for Choosing Spectacles, by George 
 
 Adams, Optician 201 
 
 II. George Adams on Short-sightedness . 203 
 
 III. Of Optometers 204 
 
 IV. Dr. Smith's Rules for Choosing Spectacles 205 
 V. Indistinctness in Old Eyes how caused and 
 
 how cured, by Dr. JuR<lN .... 207 
 VI. Curious Experiment ..... 209 
 VII. Dr. Weels on the changes which the Vision 
 of Short-sighted Persons undergoes from 
 
 Age . , 211 
 
 VIII. Mr. Ware's Observations on the Near and 
 
 Distant Sight of different Persons . .214 
 IX. Appendix to Mr, Ware's Paper, by Sir 
 
 Charles Blagden .... 218 
 
 X. Sir William Herschel on the Apertures 
 
 of the Pupil of the Eye ... . 221 
 XI. Snow Spectacles .,..., 224 
 
Viii DESdRIPTIOIS^ OF PXATES. &C. 
 
 Explanation of the Plate fronting the Title* 
 
 Fig. I. Is the Spectacle front recommended for Eyes 
 in general ; the disiance between the centres of the open- 
 ings which hold the Glasses being 2 1-2 inches, i» c. the 
 average distance between the centres of the Eyes, 
 
 Fig. II. Is a portrait of the Pupil of the Eye when in 
 a state of expansion. See Chapter XII. page 73, and No. 
 X. of the Appendix. 
 
 Fig, III. The Pupil in its most contracted state. See 
 page 73, &c. 
 
 Fig. IV. GouY emeiM double Folding Hand Spectacles, 
 See page 20. 
 
 Fig, V. A Preserver, or the First Sight for Long 
 Sighted Eyes, i.e. a Convex lens of 36 inches focus cut in 
 half — to shew its form, &c. the thickness of it at the middle 
 and at the margin of it. See page 27. 
 
 Fig. VI. The 8th Sight, for Long Sighted Eyes-r-oi- 
 12 Inches focus. 
 
 Fig. VII. No. 1 Concave, or the First Sight for Short 
 Sighted Persons, See Chapter XIII. page 85. 
 
 Fig. viii. No. 12 Concave, or the VZth Sight for 
 Short Sighted Persons, 
 
 The Plate of the Pancralic Eye-Tube and Double 
 Stars to face page 118. 
 
PREFACE. 
 
 TO BE READ AFTER THE WORK. 
 
 INow, friendly Reader, before I take leave 
 of You — after — Your deliberate perusal of 
 this Volume, — if You vote that my labour has 
 been lost, or has afforded j^ou so little plea- 
 sure, that You begin to think You would ra- 
 ther have your Seven Shillings in your pock- 
 et again, than this first part of " the Economy 
 of the Eyes^'^ under your Chin, — allow me to 
 suggest, that You ought to Lend it to every 
 body You know — to prevent others being de- 
 coyed, as in such case You will suppose you 
 have been — to buy a Book which is not worth 
 reading. 
 
 But if it so happen that fortunately for the 
 Writer, You think you have derived Amuse- 
 ment or Instruction from his Work,— if You 
 are so good as to wish to be grateful for the 
 Information which it has given you — Lend it 
 NOT — to one of those prudent folks who are 
 in the habit of borrov^ing your New Books, 
 and so contrive to become wise at your ex- 
 pense,-^but do the Author the favour to re- 
 commend all your Friends to purchase it» 
 1 
 
INTRODUCTIOK. 
 
 OENERAL OBSERVATIONS ON SPECTACLES, 
 
 Without Spectacles* all the other working 
 tools, of most Artists, soon after their 40th 
 year, would be almost useless. 
 
 At that precious period of Life, when Ge- 
 nius begins to wait upon Judgment,! the per- 
 severing Student would no longer be able to 
 enjoy the fruits of the labours of his Prede- 
 cessors, or to preserve the produce of his own 
 for the benefit of Posterity. 
 
 The accomplished Artist, almost as soon as 
 he acquires his Art, would be incapable of 
 pursuing it,— the seeds of perfection which 
 he has been industriously cultivating during 
 
 # u VVere there no other use of Optics, than the inven- 
 tion of Spectacles for the help of defective Eyes, I should 
 think the advantage which mankind receives thereby, in- 
 ferior to no other benefit whatever, not absolutely requi- 
 site to support Life." — Molyweux's Optics, 
 
 t "The exact time when years have ripened the Judg- 
 ment^ without diminishing the Imaginatwn, by good critics 
 is held to be punctually at For/?/.''— See Martij^ Scrib» 
 I.BR17S en the Dunciad, p. 55. 
 
INTRODUCTION. S 
 
 the First period of Life, would very soon af- 
 ter cease to be productive, and, but for the 
 Eye-invigorating Art of the Optician, his lat- 
 ter days would be melancholy and forlorn. 
 
 It is hoped that by a little attention to the 
 following pages, that All .who can hear,^ may 
 be enabled to procure precisely such Glasses 
 as are nriost proper for them. 
 
 Every body is in want of such Information, 
 because Nobody has given it, — therefore, I 
 have endeavoured to render it as easily at- 
 tainable, as it is universally desirable, by 
 communicating it in such plain terms that 
 Every body may understand. 
 
 The choice of Spectacles is one of those acts 
 which cannot be properly performed by 
 proxy — the Sight cannot be perfectly suited, 
 unless 
 
 " Every Eye negociate for itself." 
 
 This is so absolutely true, that not only 
 One Person cannot choose for Another — but 
 One Eye has often very little notion what 
 Glass will be best even for its own Brother, 
 so extremely does the Left Eye occasionally 
 differ from the Right. 
 
 No faculty of man varies more in its na- 
 
 * It is presumed, that the majority of the purchasers of 
 this Work, cannot See ! till they have learned how by the 
 Instructions herein given. 
 
4 INTRODUCllOB^. 
 
 ture, or is susceptible of so high a degree of 
 Improves ent and Refinement by Art, as the 
 Sense of Sight. The highest degrees of its 
 discriminating power are acquired slowly 
 and imj:^erceptiblj. 
 
 From organic imperfection and neglect of 
 cultivat'on/^ many People pass through Life 
 who (n may be said, comparatively,) never 
 See — u p. whose Eyes never have the facul- 
 ty of accurately appreciating either Form — 
 or Colour: — to very few indeed is it given to 
 perPxtly perceive and portray both. 
 
 There cannot be a more evident proof of 
 the general defect in people's Sight — than 
 the general acceptance of capricious and un- 
 reasonable Fashions, which appear to be pre- 
 valent, in proportion that they are in direct 
 opposition to all the principles of good taste, 
 and which to a fine Eye, are frequently 
 frightful, and absolutely painful to behold. 
 
 From the different modes of colouring of 
 different Artists, I suppose that the Eyes of 
 no two Painters feel exactly the same im- 
 pression of colours,~and objects, appear of 
 
 * " Every person acquainted with Optics and the nature 
 of vision, knows that what is generally comprehended un- 
 der the term Seeing, is a complex operation ; an art ac- 
 quired by degrees, in which judgment and imagination are 
 concerned together with simple perception," — GmSP on 
 Vision^ 8vo. 1796, p. 106. 
 
INTRODUCTION* 5 
 
 diflerent Colours accordingly as they are 
 illuminated with different Lights, 
 
 ^* The MoJe's dim curtain, and the Lynx's beam/' 
 
 Pope. 
 
 do not differ more extremely than does the 
 Sight of different persons — and of the same 
 persons at different Ages, 
 
 The peculiar conformation of the Eyes, 
 differs quite as much in different persons, as 
 the construction of their Noses ; — it is just as 
 impossible to guess exactly what Spectacles 
 will best suit the Sight of another Person, as 
 it is to tell what Tunes are most delightful to 
 his Ear, — or what Tastes are most delicious 
 to his Tongue. 
 
 Nothing can be more erroneous than the 
 common notion, that there is an invariable 
 Rule, that a certain form of Glass is calculated 
 for a certain Age. No Rule has more excep- 
 tions :-■ -but this Vulgar Error has been pro- 
 ductive of great and irremediable Injury to 
 the Eyes of Thousands ! 
 
 Hence, the grand desideratum, is to instruct 
 people bow to choose w isely for Themselves 
 — which, I hope, even those who are totrdly 
 unacquainted with the subject may do with 
 the most perfect ease and accuracy, by the 
 help of this Treatise, which is not published 
 for the purpose of recommending some par- 
 1 * 
 
b INTRODUCTION. 
 
 ticular Oculist—or of persuading the reader 
 that the simplest of all Optical instruments^ 
 spherical Spectacle Glasses, can only be pur- 
 chased of One Optician :— is not a collection 
 of crude conceits, — but is a plain impartial 
 statement of all the Facts I have accumulated 
 during my consideration of the subject for 
 30 years past — in which I have 
 
 '* Nought extenuated, nor set down aught in malice." 
 
 My Motto, friendly Reader, is 
 
 " Truth, tempered by Good Humour." 
 
 ^^Men must be taught as if you taught them not. 
 And things unknown propos'd as things forgot. 
 Without Good-Breeding, Truth is disapprov'd ; 
 That only, makes superior sense belov'd." 
 
 Essay on Criticism, 
 
 I do not think it is my Business — I am sure 
 it is not my Pleasure, to register the various 
 pretended improvements in Spectacles which 
 have from time to time been proposed to the 
 Public,— such as the Sympathetic Pebbles— 
 which " as the Sight alters, they will alter 
 also to the Sight, by which one pair will last 
 the wearer for Life," &c. &c. &c. ! ! ! This 
 would be irksome to the Writer, and useless 
 to the Reader. — I shall only mention the most 
 I'emarkable, 
 
 In 1758, Mr. B. Martin published a pam- 
 phlet recommending what he called 
 f* VISUAL GLA'SSES," 
 
INTRODUCTION'- « 
 
 the use of which, he assures us, would be 
 "productive of peculiar advantages,"— they 
 might be— -but, by Mr. Adam's account, not 
 to the gentlefolk who bought thenf). 
 
 " The desire men have to increase their 
 Business, and extend their Fame, has, in many 
 mstances, been the origin of alterations and 
 inventions, — injurious to Science and detri- 
 mental to the Public. 
 
 " To this we may, v/ith propriety, impute 
 the invention of Visual Spectacles. But the 
 good sense of the world, which always, in the 
 long run, justly appreciates the value of every 
 mvention, now leaves Visual Spectacles to 
 the neglect they merit." — ^G. Adam's Essay on 
 Vision, 8vo. 1792, p. 113. 
 
 I beg to be excused saying more, thpn that 
 I do not think that any of the Spectacle Glas- 
 ses which have come before my Eye, have 
 any superiority over the Common Spherical 
 Lenses now in general use. 
 
 In instituting Experiments for ascertaining 
 the distinctness and brightness of Spectacle 
 Glasses-— be extremely careful, that the Glass 
 is not only of exactly the same quality, but 
 also of exactly the same Focal length — or 
 any attempt at comparison will be useless. 
 
 If one of the Ghisses be only of a very lit- 
 tle shorter focus than the other — objects will 
 
8 INTRODUCTION* 
 
 always make a very different, and sometimes 
 a much stronger impression on the Eye. 
 
 To measure the Focal Length of Spectacle 
 Glasses^ see Chapter xv. 
 
 To give my Readers all the satisfaction in 
 my power, — I have added an Appendix—- 
 which contains sufficient corroboration of 
 what I have asserted on certain important 
 points, — because — by the time Persons want 
 Spectacles, they have generally become wise 
 " in their own conceit,"— and have picked up 
 a parcel of silly prejudices concerning them, 
 which unless completely counteracted, and 
 rectified by the invariable standard of irresis- 
 tible Truth,— will prevent their deriving that 
 benefit from this publication, which the Au- 
 thor heartily wishes that they should receive 
 to the utmost extent. 
 
 I have given Rules for the choice of 
 Glasses as relates to their degrees of Magni- 
 fying, — and have also pointed out those cri- 
 terions by which All may judge if the Glasses 
 are good — and of the right focus — and readi- 
 ly discover those imperfections in them which 
 are so common, and so injurious to the Eyes.* 
 
 To effectually eradicate erroneous opinions, 
 and to establish the Truth beyond all doubts 
 
 * See Chapter xvii. " Of the Quality of Spectacle 
 GfZawc^," and the Note at. the foot of page 36. 
 
INTRODUCTION. » 
 
 1 know is no easy task — therefore, I have 
 given an Appendix of Quotations from the 
 best Authors on the suliject— the correctness 
 of whose Judgnrient has been established by- 
 Experiment, and has been pronounced indu- 
 bitable, by universal acceptance — ?". e. from 
 the Writings of Dr. Smith ; — Dr. Jurin ; — 
 Dr. Porterfield ;— Dr. Blagden ;— Dr. Wells ; 
 — Dr. Herschell; — Mr. G. Adams, the Opti- 
 cian ; — the late Mr. Ware, the Oculist ; — and 
 Mr. Stevenson, the Oculist ; — and for many 
 valuable facts, I am indebted to that expe- 
 rienced Optician, Mr. Samuel Pierce, who 
 was upwards of Thirty Years with Mr. Jesse 
 Ramsden. 
 
 ** Palmarn qui meruit, ferat," 
 
 There could not he a more useful Charity — 
 than that of providing proper 
 
 SPECTACLES FOR THE POOR. 
 
 The Best Glasses^ set in Single-Jointed Steel 
 Frames, may be purchased wholesale at the 
 rate of 18s. per dozen Pairs; — if a Single- 
 jointed frrime is fistened round the head 
 with a Riband, it mny be kept on, ?ilmost as 
 steadily and comfortably as a Double-Jointed 
 Frame. 
 
 For the small sum of 18 Pence the Bene- 
 volent may enjoy the gratifying reflection of 
 giving an industrious Workman the power of 
 
10 ON READING GLASSES. 
 
 long continuing his labour with undiminished 
 Ability, and of earning a subsistence till ex- 
 treme Old Age. 
 
 In no way—can so much Good he done with 
 so little Money ! 
 
 "Qui Visum, Vitam dat." 
 
 The greatest part of the Disorders of the 
 Eyes of Poor People who are upwards of 45 
 years of Age, are occasioned by their strain- 
 ing their Sight for want of Spectacles, — or 
 by looking through Bad Glasses,-~or those 
 of a Focus not suitable to their Eyes : — I 
 hope when this is considered by the Over- 
 seers OF THE Poor,-— The District Societies 
 FOR Bettering the Condition of the PooRj 
 and "he Patrons of The Eye Infirmaries, 
 that they w^H' iBake the distribution of Spec- 
 tacles a part of their Bounty, 
 
 CHAPTER L 
 
 ON READING GLASSES, 
 
 For Persons whose Eyes are impaired by Age-^ 
 and Single Eye-Glasses for the Short-Sighted. 
 
 When would-be-thought-young Persons, 
 first feel the necessity of giving their Eyes 
 
ON READma GLASSES. 11 
 
 Optical assistance, they are, nevertheless shy 
 of mounting Spectacles^ which they seem to 
 consider an inconvenient manner of adver- 
 tising their Age upon their Nose — not reflect" 
 ing that they are worn by many persons who 
 have not seen half their years, but who being 
 Short Sighted, are obliged to walk about in 
 Spectacles, or forego the sight of " the Human 
 Face Divine." 
 
 However, they suppose that Spectacles are 
 such unequivocal evidence of Age and Infir- 
 mity — that they desire to dispense with exhi- 
 biting them as long as possible — therefore, 
 they purchase " a Reading Glass," and ha- 
 bitually put it up to One and the same Eye, 
 leaving the other involuntarily to wander ; 
 — after a few years, the sight of the Idle Eye 
 becomes of a different focus to that which 
 has been employed with the Glass — and is 
 often irreparably impaired. 
 
 " These puerile propensities, give rise to a 
 variety of artifices, by which each individual 
 endeavours to hide from himself and others, 
 what no artifice can conceal, j^ nd which every 
 one can discover, in all but himself ;~rhese 
 endeavours often contribute to h.jS'en the 
 Evils they are meant to conceaL Opticians 
 have daily experience of the truth of this 
 Observation, and in no instance more so than 
 
12 ON READING GLASSES. 
 
 in the preference given by many to Reading'^ 
 Glasses^ (un<ler whatever pretext it may be 
 covered) merely because ibey think that the 
 decay ot their Sight, and their advances in 
 age, are less conspicuous by using a Reading 
 Glass^thdu Spectacles : but the Eyes in endea- 
 vouring to See vi^ith a Reading-Glass are con- 
 siderably strained, and in a short time much 
 fatigued: and there. is another objection to 
 the use of Reading-Glasses, which arises 
 from the unsteadiness of the hand, and the 
 motion of the head, which occasion a perpe- 
 tual motion of the Gli^sses, for the Eye en- 
 deavours to conform itself to each change, 
 and this tender organ is thereby kept in con- 
 tinual agitation : to these evils we may add 
 the dazzling glare and irregular reflexion 
 from the surface of the Glass, which so weak- 
 ens the Eyes, that those wh\ accustom them- 
 selves to a Reading-Glass, are in a short time 
 obliged to take to Spectacles^ and to use therti 
 much older than they otherwise would have 
 done."~Mr. George Adams on Vision^ 8vo. 
 1789, p. 115. 
 
 When persons who have long patronized 
 One Eye, and slighted the Other, take to 
 Spectacles, they w^ill (generally) require 
 Glasses of a different focus for each Eye. 
 
 When You go to an Optician's to choose 
 
ON READING GLASSES. 13 
 
 Spectacles, the first thing to attend to, is to 
 look at a Book with each eye ahernately, — 
 and carefully ascertain, if You see equally 
 well, with both Eyes, with the same GlasSj 
 at exactly the same distance. 
 
 Inequality of the Focus of the Eyes^ is much 
 more common than is generally supposed, as 
 Watchm.akers, Engravers, and most Artists 
 who v\ork with a Magnifier, will tell you; 
 they generally work with One and the same 
 Eye — with which, they can see much better 
 than with the other. 
 
 After a certain Age, the relative sharpness 
 of the sight of the Eyes, varies as much as 
 does the quickness of the Ears — the Senses 
 of i/eanVig-,--and of Seeing^ begin to fail about 
 the same time; — there are kw people past 
 40 who cannot hear better with One Ear, 
 than they can with the Other. 
 
 The Eye least used, soon becomes weak, 
 and in the course of a little time almost use- 
 less. — This fact, is so little known, that I 
 have frequently heard persons who up to the 
 age of 40 have worked iheir Right Eye — 
 and finding it begin to fail, say, they must 
 begin to teach their left Eye to See— how- 
 ever, as 1 told them, they found on trial, that 
 ihe Eye which had been Idle, was much 
 9 
 
14 ON READING GLASSES* 
 
 more impaired than that which had been 
 active. 
 
 *'By ceaseless |ictlon all that is, subsists." Cowper. 
 
 Spectacles are always preferable, because 
 both Eyes* by being kept in action, are kept 
 in Health— Vision is brighter and easier, 
 and the labour of each Eye is considerably 
 lessened. 
 
 As the Eyes of Persons who have either a 
 very Long or a very Short sight, are useless 
 without Optical assistance — they should have 
 Double Folding Spectacles slung round 
 their neck ; (See Chapter IV. and Figure 
 IV. in the Plate fronting the Title 5) or, if 
 they will have a Single Eye-Glass — let them 
 take care to use it without partiality — and 
 put it to Each Eye alternately. 
 
 ^' To ascertain whether an Object seen with Both Eyes^ 
 appears brighter or larger^ than when seen with One Eye 
 only, Dr. Jurin made several experiments, which are too 
 long to insert more than the results of them. 
 
 " This difference was most conspicuous, when in making 
 the experiment by candle-light, the book vv^as at such a 
 distance from the candles as that there was scarce light 
 enough to read with both eyes ; when the column which 
 was seen by One Eye only, was not at all legible ; but I 
 could read with both ; though with some difficulty o— See 
 Dr. Smith's Optics, 4to. vol. ii. p. 107 of Remarks. 
 
 *' Though the Letters of a printed book appeared brighter 
 and stronger — yet they do not seem at all larger when 
 viewed with Both Eyes than when seen with Ol. Only,'^ 
 ■—See Pr. Priestley on Flsion, 4to. 1772, p. 689, 
 
ON READING GLASSES. 15 
 
 A Singh Glass^ set in a smart Ring, is often 
 used by Trinket-fanciers merely for Fashion's 
 sake, by folks v/ho have not the least defect 
 in their Sight, — and are not aware of the 
 mischievous consequences of such irritation: 
 — this pernicious plaything will most assu- 
 redly, in a very few Yenrs, bring on an 
 imperfect vision in One or Both Eyes. 
 
 Notwithstanding all the experience col- 
 lected during the preceding 42 Years — the 
 Third act of Life^ i. e. from 42 to 63— is as 
 seldom performed properly, as either of the 
 former. " The Art of Growing Old with a 
 Good Grace,"— I believe, is one of those, which 
 the Ancients termed "Occult Arts" — and it 
 appears to be almost as littlf understood, as 
 that of commiikicdung to our speedily pe- 
 rishing Body, the unchangeable nature of the 
 incombustible Asbestos. 
 
 Query. Which appears most ridiculous? 
 A Young Man pretending to the Sagacity 
 and Experience of Age — or an Old Man 
 affecting the Strength, and Apeing the Alert- 
 ness of Youth ? 
 
 The only way that Persons can indulge 
 their humour of appearing Purblind with 
 impunity^ is to use««» 
 
16 SPECTACLES WITH PLAIN GLASSES. 
 
 CHAPTER 11. 
 
 SPECTACLES WITH PLAIN GLASSES. 
 
 These should be kept by all Opticians, — - 
 who are not seldom puzzled and plagued by 
 more nice than wise folks, who without any 
 need of Spectacles, yet hearing their ac- 
 quaintance talk of how charminglj-they can 
 see in Glasses, they long, like '•■ the Italian 
 Count,* to be better than well" — and will 
 not believe, that although they have not the 
 least occasion for Optical as.^istance, yet, 
 without trying all sorts of Glasses, cannot be 
 convinced, that however this branch of Op- 
 tics may alleviate the infirmity of the Eyes, 
 as a Hearing Trumpet does that of the Ear, 
 yet that when the Eyes are in a healthful 
 state, they can receive no more assistance 
 from Glasses, for the ordinary purposes of 
 the Sight — than a person who is not Deaf 
 can from a Hearing Trumpet — which, al- 
 though so serviceable to a person who is 
 deaf, is not of the least use to one who is not 
 deaf. 
 
 * Whose Epitaph is — " I was weU— wished to be heU 
 ter—Took Physic — and Died." 
 
SPECTACLES WITH PLAIN GLASSES* 17 
 
 *«Why has not man a Microscopic Eye ? 
 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 l 
 God, in the nature of each being, founds 
 Its proper bliss, and sets its proper bounds." 
 
 Pope, 
 
 That ingenious Optician, the late Mr. 
 Jesse Ramsden, informed me, that he had 
 ofttimes more trouble to make obstinate and 
 ignorant persons understand that the Art of 
 Optics could not be of any service to them, 
 than he had to find Glasses for correcting the 
 most eccentric aberrations from good Vision 
 — and that he found the only plan of com- 
 pletely convincing such troublesome Cus- 
 tomers was, after he thought that they had 
 sufficiently amused themselves with trying a 
 variety of Glasses, — and had tired him, — to 
 give them a pair of Spectacles glassed with 
 plain Glass — when they would cry out with 
 rapture — "Aye, these will do, 1 can see 
 charmingly in these — why — why didn't You 
 give me these at first ? ! ! !" 
 
 Nothing, short of such ocular demonstra- 
 tion, could satisfy them. 
 
18 CASE OP A PERSON, &C* 
 
 CHAPTER III. 
 
 CASE OF A PERSON WHO COULD NOT READ lit 
 
 SPECTACLES. 
 
 Mr. R. told me that he was once strange- 
 ly puzzled, by a clever Old Gentlewoman of 
 79 j^ears of age, for whom he was requested 
 to make a pair of Spectacles. — She had ap- 
 plied in vain, to several eminent Opticians, 
 and no Glass could be found that improved 
 her Sight, 
 
 With all that Ambition to overcome diffi- 
 culties, which was the ruling passion of 
 Jesse Ramsden, he waited upon the L^dy^ 
 with several pairs of Convex, and of Con- 
 cave Spectacles, making quite sure, that 
 however others had failed, he should suc- 
 ceed, and enjoy one of those triumphs, which 
 constituted the Zest of his Existence, — but 
 after patiently trying every one of them, She 
 said with a Sigh! — " No,-— not one of these 
 will do^ — I can see better with my Naked 
 Eye. Well ! what an unfortunate Creature 
 I am, at my Age, not to be able to see to 
 read in Spectacles ! !" 
 
 Jesse consoled the Good Lady as well as 
 he could, by observing, that many at her 
 advanced age could hardly see at all : and 
 
HAND SPECTACLES. 1^ 
 
 th^f ahhou£:;h she could not see to rea ^ — — 
 Here she interrupted him with snfficie > ve- 
 hemence, and, to his extreme astonishment, 
 exclaimed, — ''Sir, You nre strangely mis- 
 taken. Sir ! — I did not tell you that I could 
 not see to Read, Sir ! — lean see to Read, 
 Sir, as well as ever I could, — I only com- 
 plained that I could not see to read in S[)ec- 
 tacles ! ! / can see to read very idbU without ! ! ! 
 but my Acquaintance say how charmingly 
 they can see with Glasses, and surely, it is 
 very hard that I cannot enjoy the same 
 Advantage." 
 
 CHAPTER IV. 
 
 HAJND SPECTACLES 
 
 Are infinitely better than any Reading 
 Glass,* however large it may be, — but are 
 
 * " The Single Convex Glasses with which some Persons 
 read, must be very injurious, if they be sufficiently large to 
 admit the same object to be seen with both Eyes. For as 
 both axes will then pass through them, one on each side of 
 the centre, the interval of the pupils will be widened, and 
 the refracting power of the Eyes be diminished ; so that 
 here a disadvantage is to be added to the prejudice of the 
 convexity of the Glass, — not a benefit to be placed against 
 It, as in the case of Common Spectacles for the Long- 
 Sighte(j."—Dr. W. C. Wells on Vision, 8vo. 1792. p. 130. 
 
20 HAND SPECTACLES, 
 
 Still, not so comfortable to the Sight as Spec^ 
 iacles on J^ose — unless considerable care is 
 constantly taken to always hold them exact- 
 ly parallel with, and at exactly the same 
 distance from the Eyes. 
 
 Double Folding Hand Spectacles (see Figure 
 IV. in Plate facing the Title) are preferable 
 to a Single Eye-Glass^ for Short'sighted per- 
 sons to view pictures, &c. &c. Moreoverj 
 the use of them is not so likely to be set 
 down to Impertinence and Affectation— a 
 censure which all persons expose themselves 
 to, as often as they stare about them with 
 ^'a Quizzing Glass.^^ 
 
 The ingenuity of the Optician is often dis- 
 played in the formation of Hand Spectacles, 
 and a variety of highly-finished Gold and 
 silver mountings have been contrived — but 
 unless the Glasses are defended by a case, as 
 in the frame portrayed in Figure No. IV. in 
 the Print facing the Title, they will ,soon 
 become scratched and spoiled. The Pearl 
 frame is the most elegant. 
 
SYMPTOMS OF THE EYES, &C. 21 
 
 CHAPTER V. 
 
 SYMPTOMS OF THE EYES REQUIRING SPECTA- 
 CLES TO READ WITH. 
 
 The ni^tural decay of the Sight commen- 
 ces, in Common Eyes, very soon after '^ the 
 Meridian of Life," which, according to those 
 who train men for Athletic Exercises, and 
 according to Dr. Jameson,* is about our 
 28th, — according to others,! about our 35th 
 Year. 
 
 " Tht Crystalline Humour is clear and 
 transparent like water — (ill about the 25th 
 or 30th year of our age, when it begins to 
 become a little Yellow towards the centre, 
 which Yellowness grows gradually deeper 
 and deeper, and extends more and more 
 towards the surface, in so much that Dr. 
 Petit found that the Crystalh'ne of a man 
 81 years old, resembled two pieces of beau- 
 tiful Yellow Amber." — Dr. Porterfield 
 on the Eye, 1759, 8vo. vol. i. p. 229. 
 
 The commencement and progress of the dete- 
 
 * See Dr. J. on the Changes of the Human Body, 8vo. 
 1811, p. 89. 
 
 t See 4th Edition of " The Art of Invigorating and 
 Prolonging Life-^''^ by the Author of this Work, "l2mo, 
 1822, p. 4ti. 
 
22 SYMPTOMS OF THE EYES REQUIRING 
 
 rioration of the Sights depends upon the 
 health of the individual — upbn the original 
 formation of the Eye,-- and upon how it has 
 been used. 
 
 Some Eyes, at 30 years of Age, require 
 the aid of art as much as others do at 60, — 
 while the Sight of some persons continues 
 almost as perfect at 50 as it was at 30. 
 
 The average period of the Eyes requiring Spec- 
 fades to read with^ is about the 45th year* 
 
 Nature has decreed, that soon after our 
 40th year, the most perfect Eyes shall no 
 longer retain the privilege she gives to Youth, 
 of the power of adjusting them to See dis- 
 tinctly at different distances : — this range of 
 accommodation diminishes gradually, till it 
 fails almost entirely—those to whom it is 
 given to continue to discern distant things 
 distinctly ,~no longer see those which are 
 near distinctly. 
 
 Very few persons past the age of 40 can 
 see quite so well by Candle-light, as they 
 could before that Age- — those who can, — 
 will generally find that there is a small de- 
 gree of Shortness in their sight, which is the 
 cause of their possessing that advantage lon^ 
 ger than persons in general do— -if they 
 will try that very shallow Concave which is 
 ealledj by OpticianSj '^Ko^ 0. Concave^'^ or 
 
SPECTACLES TO READ WITH. 23 
 
 ^'' Half a Number'^ — they will find it give a 
 decided outline to distant objects, which they 
 never saw defined sharply before. 
 
 However, people who do not use their 
 Eyes for minutely examining Near,- — or for 
 accurately delineating Distant objects, — are 
 quite unconscious of the finer perceptions of 
 a fine and cultivated Eye — and are equally 
 insensible to the smaller gradations of the 
 deterioration of their Sight, and happily 
 suppose that '• they have a Good Eye,*" 
 while, as Beatrice says, 
 
 <' They can see a Church b\- Day-light." 
 
 There are several symptoms, too evident, 
 even for the Self-love of the vainest and the 
 weakest to mistake, by which All persons 
 will easily perceive when they really require 
 the assistance of Spectacles. 
 
 The first Indication of the Eye beginning to 
 he impaired by Age^ is that when You wish to 
 read a small prints You are obliged to remove 
 it further from your Eye than You have 
 been accustomed to do, and desire the aid of 
 plenty of Light ; and on looking at a near . 
 object, it becomes confused, and appears to 
 have a kind of mist before it, and the letters 
 of a Book run one into another or appear dou- 
 ble, &c. ; and, by Candle-light,* You catch 
 
 ^ ^* There are many who find the effect of Candlc-light 
 
24 SYMPTOMS OF THE EYES REQUIRING 
 
 yourself holding a Book, &c'. close behind 
 the Candle — and, that you begin to admire 
 the ingenuity of the Gentleman who invent- 
 ed Snuffers. 
 
 You will begin to feel the absolute nece sify of 
 using Glasses^ when you want to read a small 
 print by Candk-light^ for Twelve months before 
 you require their assistance by Day -light. —See 
 Cumumbra Lamp. • 
 
 If You obstinately strivQ against Nature, 
 and barbarously refuse your Ej^es that assist- 
 ance from Art — which will-enable You to see 
 with great ease, but without which, you can- 
 not see without great ditficulty — You will act 
 as absurdly, as if You refused to eat when 
 hungry, or to sit down when You are tired— 
 and will soon strain and weaken your Sight, 
 which will receive more injury in a few 
 Months by such forced exertion, than it would 
 in Years, if assisted by proper Glasses which 
 render Vision easy. 
 
 so different from the purer light of Day^ that they are 
 obliged to use Spectacles by night, though they can do very 
 well without them in the day. These, when the eye has 
 become more flat, will find it advisable to have two pair of 
 spectacles, one to use by day, the other appropriated for 
 the night : by this means, nearly the same quantity of Light 
 may be brought to act upon the retina at one time as the 
 other ; thus the eyes will be less fatigued, and longer main- 
 tain their natural Vigour." — Mr, G. Adams on Vision, 
 Bvo. 1789. p. 108. 
 
SPECTACLES TO READ WITH. 25 
 
 However, some people seem to be about 
 as unwilling to acknowledge this Truth — as 
 they are to confess thai they do not feel quite 
 so frisky as 45 — as they did at 25. 
 
 The common objection which people make 
 to put on Spectacles, is, that '•'- if They once 
 begin to wear them, They are afraid they can 
 never leave them off as^ain :" — this is true 
 enough ; — but why should they ? if by such 
 aid, their Sight is relieved and preserved, 
 and They are enabled to see easily and dis- 
 tinctly, and when they attempt to read with- 
 out, their Eyes ache, — their Head aches, — 
 and every bit of 'em aches. 
 
 A man afflicted with incurable Lameness, 
 who cannot move without Crutches, would 
 act just as wisely, in refusin^.^; to avail himself 
 of them, — because he can never hope to walk 
 again without; 
 
 "Timely assistance from Glasses will ease 
 the Eyes, and in some degree check their 
 tendency to grow flatter — whereas, if they be 
 not assisted in time, the flatness will be con- 
 siderably increased, and the Eyes be weak- 
 ened by the eflorts they are compelled to ex- 
 ert ; all delaj^ is dangerous, and the longer 
 those who feel the want of assistance, defer 
 the use of Spectacles^ the more they will in- 
 3 
 
26 SYMPTOMS OF THE EYES, &C» 
 
 crease the failure of the Eye." — Adams on 
 Vision^ 1792, 8vo. p. 109. 
 
 " The change in the conformation of the 
 Eyes, which renders Spectacles useful, seems 
 to be one of those which Nature has destined 
 to take place at a particular period of Life, 
 and to which there is no gradual approach 
 through the preceding course of Life. A per- 
 son for instance at 40^sees an object distinctly, 
 and at the same distance that he did at 20. 
 When he draws near to 50, the change I have 
 spoken of, commonly comes on, and obliges 
 him in a short time to wear Spectacles. As it 
 proceeds he is under the necessity of using 
 others of a higher powder. But, instead of 
 supposing that his Sight is gradually becom- 
 ing worse, from a natural process, he attri- 
 butes the increase of the defect in it, to his 
 too early and frequent use of Glasses. Upon 
 the whole, I should draw this inference from 
 w^hat has been said, that — no person whose 
 Sight begins to grow Long^ ought to be in the 
 least prevented from enjoying the immediate ad- 
 vantage which Spectacles will afford him^ by the 
 fear that they will ultimately injure his Eyes*^'^ — - 
 Dr. Wells on Vision. 
 
OF PRESERVERS. i« 
 
 CHAPTER VI. 
 
 OF PRESERVERS. 
 
 By the help of Convex Glasses^ of 36 or SO 
 Inches focus, if your Eyes are in the state 
 above mentioned, You will be enabled to 
 read with the same ease, and at the same dis- 
 tance, that you did before your Sight was 
 altered by the inevitable decrees of Old 
 Time — such Glasses, will make things appear 
 clear, and distinct as they did before your 
 Eyes w^ere impaired ; and if judiciously cho- 
 sen, lessen the labour of the Eyes — and ena- 
 ble them to do their work with more ease, 
 and therefore, I suppose, do, in a certain de- 
 gree, preserve the Sight, 
 
 This Title of Preservers, which some sa- 
 gacious name-giver gave to Spectacles of 36 
 Inches focus or the First Sights is an admira- 
 ble appellation to attract the attention ofpeo- 
 
 * Of Convexes^ — i» e. Glasses for assisting those Eyes 
 which are too Long Sighted — or what is commonly called 
 an Old Sight, are named from their focal length ; the high- 
 est num.ber, No. 36, niagnifies least, and is called the 1st 
 Sight : See Figure 5 in the Plate facing the Title, 
 
 Of Concaves, i. e. Glasses for a Short Sights — that which 
 is the least concave, and gives the least assistance to the 
 Eye, is called No, 1, See Figure 7 in the Plate fronting 
 the Title, 
 
28 OF PRESERVERS. 
 
 pie — but is equally applicable to all the fol- 
 lowing gradations of Glasses ; — for the term 
 is generally misunderstood,^ — people seem to 
 suppose, that Speciacies of 36 Inches focus, 
 have the magic power of arresting the pro- 
 gress of that failing of the faculty of Sight, 
 which is one of the natural and unavoidable 
 consequences of Age. 
 
 When once the Sight begins to fail, it con» 
 tinues to decay, till in extreme Age, our Eyes, 
 like our other Senses, — become of almost as 
 little use to us, as they were in our Infancy, 
 
 It is very common for Persons after they 
 have worn Spectacles of 36 Inches focus for 
 a Year or two, to complain that they think 
 that '' their Glasses cannot be of the right fo- 
 cus for their Eyes, for when they do not wear 
 them, they certainly cannot see so well with- 
 out them as they did before they used them, 
 therefore, — they certainly cannot be Pre- 
 
 After the process of deterioration has been 
 proceeding for 12 months — it would be won- 
 derful if it had not made some perceptible 
 progress ! — It is as ridiculous, to expect that 
 it i.'. in the power of an Optical Instrument to 
 eni-rely prevent the Eye undergoing that in- 
 var ably certain, although alm.ost impercepti- 
 ble change which accompanies the advance 
 
OF PRESERVERS, 29 
 
 of Age, as it would be to suppose that Art 
 can prevent the failing of any of our other 
 faculties. 
 
 I make tbeseremarks, because, 1 know that 
 the prepossessing term has induced sorn? ex- 
 cellent Artists,* who were naturally extreme- 
 ly anxious about their Eyes — (their Eyes are 
 their Estate, the mainspring of their Fame 
 and of their Fortune) — to wear Spectacles 
 before they wanted them, 
 
 Mem.- — The premature use of Spectacles^ is 
 as pernicious to the Sight, as Physic to the 
 Stomach of a Man in Health, and as absurd, 
 and as uncomfortable, — as it would be to put 
 on a Fur pelisse at Midsummer, as a Preser- 
 -ver against your feeling the Cold of Christmas. 
 
 * See Chapter xiii. The Art of Seeing, &c. 
 
FOCAL LENGTH OF 
 
 CHAPTER VH. 
 
 TABLE 
 
 Of the Focal Length of the Convex or Magnify- 
 ing Glasses commonly required at Various 
 
 Ages. 
 
 Years of Age- 
 
 Inches Focus 
 
 of 
 Convexes. 
 
 Remark. 
 
 40 
 45 
 50 
 
 36 
 30 
 
 24 
 
 Convex Spectacles are 
 seldom wanted, except to 
 read bv Candle-light till 
 45 or 50. 
 
 55 
 
 20 
 
 
 58 
 
 18 
 
 
 60 
 
 16 
 
 
 65 
 
 14 
 
 
 70 
 
 12 
 
 
 75 
 
 10 
 
 
 80 
 
 9 
 
 
 85 
 
 8 
 
 
 90 
 
 7 
 
 
 100 
 
 6 
 
 * 
 
 * These three last deep Lenses are very rarely required 
 except for Couched Eyes, *^One focus is seldom sufficient 
 to enable those who have undergone the operation of 
 Couching, to see objects at different distances — who gene- 
 rally require one pah: of Spectacles for near^ and another 
 
CONVEX GLASSES, &C. 31 
 
 The above Scale was given to me by an 
 eminent Optician, as the average resuhs oi, 
 upwards of 50 Years' very extensive Experi- 
 €iv e : — and I believe it is as good a General 
 Rule as can be written ; but, as 1 have ob= 
 scived in the Introduction to this work — Ko 
 General Rule has more Exceptions* 
 
 " No regular estimate can ever be esta» 
 bl'shed as an absolute criterion, either of the 
 
 for distant, objects. The foci which are used lie between 
 6 and 1^ inches.'' — G. Adams on Vision, 8vo. 1792, p. 126. 
 
 If you are a Laughing Philosopher, gentle Reader, You 
 will not be very angry with the Author for inserting the 
 following Anecdote :~ 
 
 *' In the city of Leyden, in Holland, a young woman 
 lost her sight from a cataract ; tlie operation of couching 
 was successfully performed upon her Eyes, and she reco- 
 vered the use of them; but it appeared that the Visual Or- 
 gan (as is usual in such cases) was not completely restor- 
 ed to its primitive condition. Some very singular and un- 
 accountable anomalies in her Vision presented themselves, 
 which not a little puzzled the curious in Physiology and 
 Optics. 
 
 " It was ascertained that her Eye w^as able to define a 
 certain class of very minute objects with abundant accu- 
 racy, such as the Eye of a needle, for example, which she 
 could thread as well as ever ; but on presenting her with a 
 Book, it was evident that she could not distinguish a sin- 
 gle letter, but complained that she could see nothing but a 
 heap of odd marks. 
 
 " These facts, no less strange than true, naturally excit- 
 ed an intense interest among the Medical Piofe?;sors and 
 Students; every one was anxious to distinguish himself by 
 affording a satisfactory elucidation of these inexplicable 
 phenomena. 
 
->^ FOCAL LENGTH OF 
 
 want of, or for the change of Spectacle 
 Glasses ; because, the failure or the strength 
 of the Sight, varies so considerably with dif- 
 ferent people : — several youths under 20 
 years of Age, have applied to me,,who could 
 not see either to read or Vvrite. without very 
 strong Magnifiers of 6 or 8 inches focus- 
 while I have met with other persons who 
 have arrived at 80, able to read a small 
 print without any.'' 
 
 " That celebrated Preacher, the Rev. Mr. 
 RoMAiNE, Rector of Sl Ann's Blackfriar^s^ 
 who died in the Year 1795, having attained 
 the age of 81, could read the small print in 
 
 ^^ A hundred theories were framed— every one more inge» 
 Bious than the other. The Professors Von KracbraneRj 
 and PuzzLEDORF, favoiired their pupils with most excel- 
 lent lectures on the subject, with which they were greatly 
 edified. However, none of the disputants succeeded in 
 establishing a Theory which met with univei&al approba- 
 tion. Many of the vulgar still chose to think that all the 
 said Theories might be liable to the old objection (howev- 
 er satisfactory and plausible they might appear,) Viz,— 
 ^ That they were not True.' 
 
 *' Matters vvere in this state, when a mischievous rog;ue 
 of an Irish student, who took a singular delight in ridi- 
 culing every thing learned and philosophical, contrived to 
 insinuate himself into the confidence of a younger brother 
 of the Patient's by a present of an extra portion of Dou- 
 "blegiit Gingerbread, which so entirely won the Youngster's 
 heart, that he confessed (though v/ith some difjficulty) that 
 to the best of his belief, his Sister " Sarah had 7iever learn- 
 ed to Read,^^ hut unwilling to acknowledge her ignorance, 
 hM mad€ him and all the Family — promise not to telL" 
 
CONVEX GLASSES, &C. 33 
 
 a pocket Bible, unassisted by Glasses, even 
 to the last. He never wore Spectacles, nor 
 wanted any." 
 
 " I knew a Gentleman who took the assist- 
 ance of Glasses at about 40 years of Age ; 
 these after some time he exchanged for older 
 ones; and although he lived to be 84, they 
 were never afterwards altered, and his sight 
 continued sound and healthy. Knowing this 
 circumstance, I had the curiosity to measure 
 the focus of the Glasses, and found it was 14 
 inches, which he had been using quite satis- 
 factorily for upwards of 40 years." 
 
 " Another Gentleman, now living, with 
 whom I am well acquainted, did not take lo 
 the use of Spectacles until he was 55 years 
 of Age : since that period, his Glasses have 
 been twice or three times changed ; and al- 
 though he is now but little short of 87, yet 
 the Glasses which he generally uses, and 
 which he can see the best with, are 16 inches 
 focus." 
 
 For these last Remarks I am indtbted to Mr. 
 Samuel Pierce. 
 
 The time that the First Glosses of 36 inches 
 focus will sufficiently assist the Si^ht-— depends 
 on the peculiar nature of the Eyes-- on tne 
 
34 WHEN TO CHANGE FIRST SPECTACLES. 
 
 wear they have previously had — on their 
 subsequent exertions-^ancl on the ConstitH-» 
 lion and general Health of the Individual, 
 
 Persons of a strong Constitution, who make 
 more use of their Legs and Arms, than they 
 do of their Eyes, seldoro want Spectacles so 
 soon,— or want to change them so soon, as 
 the Studious and those Artists who are much 
 employed in fine works, which require not 
 only the most earnest exertions of the Eyes, 
 but also the application of a powerful Mag- 
 nifier. 
 
 As a general Rule, the first Spectacles will 
 last You for reading by Daylight, during 
 your first apprenticeship to Old Age — u t* 
 about 7 Years* 
 
 CHAPTER VIIL 
 
 WHEN TO CHANGE THE FIRST SPECTACLES, 
 FOR STRONGER MAGNIFIERS. 
 
 When You find a recurrence of the Symp- 
 toms which first prevailed upon You to wear 
 Spectacles — and begin to see but little or no 
 better with the first Glasses, than you then 
 did with your naked Eye— your Eyes re- 
 quire Tht Second Sight of 30 inches focusv--« 
 
FOR STRONGER, MAGNIFIERS, 35 
 
 But, I most earnestly entreat my friend the 
 Reader, to be content with as little assistance 
 as will enable him to read a Newspaper com- 
 fortably by Candle lighi,^ at about the sanie 
 distance he did before his Sight was impair- 
 ed — from 8 to 10 inches, is the mean dis- 
 tance at which common Eyes, in their mean 
 state, see most distinctly. 
 
 When you find that the First Sight of 36 
 Inches focus, is hardly sufficient help to read 
 by Candle-light— to examine any very mi- 
 nute object — i. e. to make pens, &c., You 
 may get the Second Sights of 30 Inches focus. 
 — But pray — only use them, for purposes for 
 which you find the First Sight is quite insuffi- 
 cient. 
 
 'The following Advice of Mr. George 
 Adams, the Optician, is excellent : — 
 
 " Those who are careful in following a re- 
 gular gradation in the change of their Glasses, 
 may preserve their Eyes to the latest period 
 of Old Age, and even then be able to enjoy 
 the comforts and pleasures which arise from 
 distinct vision. Do not therefore precipi- 
 tate these changes, lest you should absorb 
 too soon the resources of Art, and not be 
 
 * See Eeading Candlestick or Lamp, in The Table of 
 Contents, 
 
:Vo MY GRANDMOTHER S SPECTACLES^ 
 
 able to find Spectacles of sufficient power.'^ 
 G. A. on Vision, 8vo. 1789, p. 108. 
 
 Many persons have irreparably injured 
 their Eyes, and indeed have worn out their 
 sight prenriaturely — by beginning with Spec /a- 
 cles of too Short focus, i. e. which magnify 
 too much, or as the common expression is, 
 are too Old* 
 
 Nature soon bends to Custom. Eyes which 
 have been excessively stimulated by too deep 
 Magnifiers, seldom or never recover their 
 elasticity. 
 
 CHAPTER IX. 
 
 MY GRAJ^DMOTHEKS SPECTACLES. 
 
 How often a story like the following, is 
 told to Opticians* by persons coming to 
 change, what they call their First Specta- 
 cles. 
 
 * There are very few Opticians but what must have seen 
 instances of Persons who by habituating their Eyes to 
 Glasses of too short a focus, i, e, of too great a magnifjnng 
 power, have so injured those tender organs as to deprive 
 them of future assistance from Glasses, 
 
 This not unfrequently happens to Bargain-hujntters — 
 who buy their Spectacles of— Hawkers and Pedlars'—Toy- 
 shops^ Dealers in Marine Stores^ &c. 
 
MY grandmother's SPECTACLES. 37 
 
 When their Optical friend expresses his 
 surprise to find them choose very old Glasses 
 of 12 or 10 inrhes focus, instead of the Se- 
 cond Sight of 30 inches focus, 
 
 They say, " Why, when I thought that I 
 began to want Glasses, — I recollected — that 
 there was a pair of nice J^ew Spectacles in my 
 Grandmother's old Bureau, — and I had often 
 heard the old Gentlewoman say, when she 
 was past her 70th year— that she could still 
 see to read Charmingly with her Jfew 
 Spectacles ! — and so I thought, that I could 
 not do better than use those Glasses whose 
 sight-restoring power I had been Eye-witness 
 of. — I naturally thought, that they must sure- 
 ly be capital Spectacles which enabled so 
 Old a Person to see so well : and when 1 put 
 them on, I was not disappointed — for they 
 made every thing appear very big indeed, 
 and I could read the smallest print very 
 nicely indeed — better than I had been able 
 to do with my naked Eye for a long time 
 past." 
 
 I must now give you a hint, gentle Reader, 
 — however improper such mighty Magnifiers 
 may be for your Visual Organs — preserve 
 them with all care — the occasional use of 
 them will greatly contribute to preserve that 
 Grand Organ your Stomach. No " Grand 
 4 
 
38 MY grandmother's spectacles* 
 
 Gourmand?'^ who has any pretensions to pru- 
 dence, should venture to attend a tur.tle- 
 FEAST* without such Sentinels on his Nose— 
 they are absolutely as indispensable a part 
 of the paraphernalia of the Banquet — as a 
 Plate or a Spoon ! 
 
 Tht Eye is a mighty and merciless enemy 
 to tht Stomach — alas ! as the Proverb says, 
 " it is bigger than the Belly." Now even 
 supposing your Eye to be as big again, — 
 with these powerful Spectacles, your Eyes 
 may be filled with delight, and your Stomach 
 also : for the former, will imagine that while 
 you have been leisurely sipping a small Soup- 
 plateful, you have been swallowing an im- 
 mense Tureenful : — What a beautiful delu- 
 sion ! at once, equally delightful to your Sto- 
 mach, your Eye, and your Tongue — equally 
 
 * " Nothing is more difficult of digestion, or oftener re« 
 quires the aid of Peristaltic Pfrsuaders, than the gluti- 
 nous Calipash, which is considered the " Bonne Bouche'^ 
 of this surfeiting Farrago." 
 
 The usual allowance at a Turtle-Feast is 6 Pounds 
 live weight per head : — 
 
 " At the Spanish Dinner, at the City of London Tavern, 
 in August 1808, — 400 Guests attended, and 2500 pounds of 
 Turtle were consumed/' — See Bell's Weekly Messenger 
 for August 7, 1808. 
 
 Epicure Quin used to say that it was " not safe to sit 
 down to a Turtle Feast at one of the City Halls, without 
 A Basket'hilted Knife and Fork.'''' — From page 251 of the 
 5th Edition of The Cook's Oracle, 12mo. 1823, 
 
MY grandmother's SPECTACLES. 39 
 
 magnifying the pleasure of those two most 
 troublesome of the Senses — the Sight and 
 the Taste— which ^re exerihe most irration- 
 ally importunate m ttie r demands, and the 
 Biosi difficult to be satisfied! 
 
 Whenever your Tongue cries out for more 
 dainties, than your Stomach has previously 
 plainly told you is agreeable to it — lo settle 
 ail the difference of their demands to their 
 mutual satisfaction, you h^ve nothing to do, 
 but to— put on your Spectacles, and you may 
 set to at Calipash and Calipee with impunity 5 
 for, they will make "a little lark" look like 
 ''A LARGE FOWL," 
 and " A PENNY roll" ^s big as 
 '' A QUARTERN LOAF ! ! !" 
 
 Some Philosophers have said, that Pain 
 is only imaginary,— we may as justly believe 
 the same of Hunger ; and if a Gentleman 
 who eats only an Ounce of Mutton, imagines, 
 by the aid of these magnifiers, that he has 
 eaten a Pound—his Hunger, ought, to be as 
 fully satisfied. 
 
 Mem. The addition to your Optician's 
 Bill — will soon be overpaid by the subtrac- 
 tion from your Butcher's and Baker's. 
 
40 HINTS TO PERSONS CHOOSINO 
 
 CHAPTER X. 
 
 HINTS TO PERSONS CHOOSING SPECTACLES T0 
 READ WITH. 
 
 A PART of the paraphernalia of an Opti* 
 clan's counter, is a Book^ of rather a small 
 print, (about the size of the Note at the foot 
 of this Page) — which is presented to those 
 who come to choose Spectacles- — and such 
 Glasses are very properly recommended, as 
 will enable the person to read it — at the 
 same distance, and with the same ease, that 
 he could before his Eyes were impaired, L «• 
 through which the Letters appear perfectly 
 distinct, and of their natural size. 
 
 The first thing to attend to, is to look at a 
 Book with each Eye alternately (shutting the 
 other), and carefully ascertain, if you see 
 equally well, with both Eyes, with the same 
 Glass, at exactly the same distance. Per- 
 sons are quite unconscious of the frequent 
 inequality in the focus of the two Eyes till 
 they thus try them separately ; when they 
 often find that a Glass which will do very 
 well for one Eye — is of little or no use to 
 
 * The Authok* will be sadly disappointed if in future this 
 Work is not the Volume chosen for that purpose. 
 
SPECTACLES TO READ WlTH. 4l 
 
 the Other, which to be rendered effective 
 must have a Glass of a different focus. 
 
 With Glasses not Convex enough^ or, accord- 
 ing to the common expression, which are 
 too Youngs You will not see clearly, unless 
 the Book is placed so far from your Eyes, 
 that the Letters cannot be seen distincily. 
 
 With Glasses too Convex — or too Old — You 
 will be obliged to brino; the Book nearer to 
 your Eyes than you did when your Sight 
 was good- — and the Letters will appear larger, 
 than they really are. Spectacles which 
 magnify too much, v/ill strain the Eyes even 
 more than those which do not magnify 
 enough — -and instead of retarding, will acce- 
 lerate the defect which age brings on. 
 
 "When persons apply to an Optician for 
 Spectacles to read or work with ; they 
 should clearly understand, that the Objects 
 for which such Spectacles are solely calcu- 
 lated, are not placed more than 12 or 14 
 Inches from their Eyes — i, e. whether Read- 
 ing, Writing, Sewing, &c. for there seems to 
 be a natural impulse in most persons, that 
 after a printed Book has been handed them 
 for trial to read, they will presently look off 
 ■ — to some object on the other side of the 
 Room, or across the Street, and say, 'Why 
 now I can see well enough to Read vyith 
 
42 HINTS TO PERSONS CHOOSING 
 
 these Glasses— but I cannot discern what 
 that word is over yonder Door ;' and the 
 Optician h.^s oftentimes no little trouble to 
 convince them, that such Spectacles are not 
 intended to show objects at a distance— to 
 see which, their Sight is as strong as ever; 
 and in fact, that they can see distant objects 
 best with their naked Eye." 
 
 " A person in business, with whom I was 
 acquainted, began to want the common Opti- 
 cal assistance, especially for Writing, when 
 about 40 years of Age— -tlie Glasses he first 
 used were of 30 Inches focus, but he soon 
 found them useful to look at the labels on the 
 parcels of Muslin arran2;cd on the ^h^lves 
 around his Shop: after a while, he found it 
 easy and convenient to keep them on during 
 the Day, to serve his Customers, or occa- 
 sionally to look along the Street for a passing 
 friend. Another pair of deeper focus, was 
 a repeated necessi^ry consequence, for the 
 mechanism of his Eyes naturally formed 
 themselves to the power of the Convex 
 Glasses, and his Eyes still growing older— 
 and strained by too strong excitement, at last 
 w^ould not perform their office distinctly, 
 unless assisted by Spectacles of 1 1 Inches 
 focus — so that he became literally half=blind 
 in the course of about 10 Years/ 
 
SPECTACLES TO READ WITH. 43 
 
 " This, is not a very singular,- — but a very 
 common case, — »and one of the most frequent 
 causes of irreparable injury to the Eyes, 
 and is one of the first cautions to be given to 
 those who are choosing Convex Spectacles, 
 
 "From not being av\are ot this, I have 
 known several Painters and other Artists, 
 who have, in their natural anxiety to see as 
 well as possible, irremediably injured their 
 Sight — so that when they became 60 or 70 
 years of age, they were obliged to use Two 
 half glasses of different foci fixed in the 
 rings of a Spectacle frame— the upper half 
 to help them to observe a distant picture or 
 sketch, &c. and the lower half to transmit it 
 to canvass." — Mr. S. Pierce. 
 
 With such divided Glasses, it requires con- 
 siderable attention to raise or depress the 
 Eyes sufficiently, so as only to look through 
 one half,~and that the rays from the other 
 half, may not confuse the Eye and distress 
 its adjustment—which would be extremely 
 perplexing and detrimental to the Eyes, to 
 which it would be as bothering, as it would 
 be to the Ears to have two Barrel Organs at 
 the same m.oment,— One playing '^ Sally in 
 our Ally^'^ '—dind the Other " Ally Croaker J^'^ 
 
 There have been several other plans for 
 iDbtaining tne convenience of Two pairs of 
 
44 HINTS TO PERSONS CHOOSING 
 
 Spectacles in One frame — bv having the 
 glasses to turn up on the side, Stc. but all 
 such contrivances are at the expense of the 
 Eye — the Magnifying power of Spectacles 
 has also been made to vary from 36 to 12 
 Inches focus, by having two Eye-glasses, of 
 72 Inches focus, one before the other, and 
 separating them; but the vision cannot be 
 so good as with the simple single Eye-glass 
 •—and those who value their Eyes— will use 
 no other. 1 think the most convenient plan, 
 and also the least injurious to the Eyes, 
 would be to have a pair of Spectacles glassed 
 with Glasses of the focus required to see the 
 distant object or sketch, &:c. and other Glas- 
 ses in a frame attached to the Spectacle 
 frame, and moving on hinges — which, when 
 brought down before the Glasses fixed in the 
 Spectacle fr me— might make combined the 
 focus required for painting the Picture, and 
 which, when it was requisite to refer to the 
 Object or Skc ch, might be turned up on the 
 Foreher^d, quite out of the way. 
 
 " The late President of the Royal Acade- 
 my — Benj^^min West, Esq. was in the habit 
 of using Divided Glasses for many years ; the 
 upper half was of 30 inches focus, and the 
 lower of 12. But for some time before his 
 death, which happened when he was about 
 
SPECTACLES TO READ WITH. 45 
 
 90 years of age, he had the upper half of 30 
 inches focus, and the under hnlf of only 8 
 inches focus." The Glasses were round and 
 an inch and a half in diameter. 
 
 The above account of Mr. West's Specta- 
 cles is another of the contributions of Mr. S. 
 Pierce, who made (he Spectacles. 
 
 By trying a variety* of Glasses at an Op- 
 tician's, the Sight soon becomes confused 
 and tired, and for the moment quite unfit to 
 appreciate with proper accuracy, what Glas- 
 ses are exactly the best for it. 
 
 I advise persons who have never worn 
 Spectacles — or are uncertain what Glasses 
 will suit their Eyes best, to borrow One of 
 the Sets of Glas^es^ which consist of Specta- 
 
 * Though in the choice of Spectacles, every one must 
 finally determine for himself, which are the Glasses through 
 which he obtains the most distinct Vision ; — yet some con- 
 fidence should be placed in the judgment of the A)tist of 
 whom they are purchaseci, and some attention paid to his 
 directions. 
 
 '* By trying many Spectacles the Eye is fatigued, as the 
 Pupil varies in size with every different Glass, and the 
 Eye endeavours to accommodate itself to every change 
 that is produced. Hence th^- puichasei often fixes (. pon a 
 pair of Spectacles not the best adapted to his Sit^ht^ but 
 those which seem to relieve him most, while his Eyes are 
 in a forced and unnatural state ; and consequently, when 
 he gets home, and they are returned to their natural state, 
 he finds what he had chosen, fatiguing and injurious to the 
 sight*" Mr. G. Adams on Vision^ 8vo, 1789j p. 96. 
 
4G HINTS TO PERSONS CHOOSIN© 
 
 cles, of regular gradations of power, set in a 
 frame — the first set of Convexes usually con- 
 tains the first Seven Glasses mentioned in the 
 Table at page 30 — or, if these cannot be had 
 — choose at the Opticians, those Spectacles 
 which they think they can see best with, 
 and take home with them also. Two other 
 pairs, one a degree more, the other a degree 
 less Convex, or Concave, as they happen to 
 be either Long, or Short-Sighted : — they 
 should iry these repeatedly for whatever 
 purpose they wish to employ them : — should 
 take care, that the Glasses they try are all 
 perfectly clean — and that they hold them as 
 close and parallel to the Eye as Spectacles 
 are placed. 
 
 They will probably find, if they try them 
 by Candlelight, especially with a very small 
 print or fine work — that one degree of mag- 
 nifying power more than they require by 
 Daylight^ will show very small objects most 
 distinctly — hut I protest against such indul- 
 geri' e a^ first- — when the Sight is much im- 
 pairs d by Age- — a pair of Glasses for use by 
 Day. and ar.other ibr Night, are advisable 
 coniforis for the Eyes. 
 
 The best plan for the Preservation of the Eye ?, 
 ' — is not to employ them in any work at Night 
 that gives them any trouble :— let all Busi- 
 
SPECTACLES TO READ WITH. 47 
 
 ness which requires intense attention, such as 
 mending Pens, &c. be done by ^' the better 
 Day." 
 
 At any Age, — the less the Eyes are ac- 
 tively employed at Night, the better — after 
 the labours of the Day, the Eye participates 
 in that languor which every other part of the 
 System suffers, and the tone of the Visual 
 Organ is comparatively feeble-— therefore 
 avoid as much as possible, reading a small 
 print, or any business which requires the 
 earnest exertion of the Eyes — and always 
 use a shaded light. 
 
 The moment that your Eyes, by beginning 
 to feel hot and fatigued, give you a hint, that 
 they have done as much work for you as is 
 agreeable to them — leave off exerting them. 
 
 Forcing the Eyes to Work at jVight^^ even 
 for a few moments after they are tired, — w^ill 
 often, put them out of humour for the whole 
 of the following Day, and is of all Eye-spoil- 
 ing Acts the most mischievous ; — w^ant of 
 Mercy in this respect, has prematurely ruined 
 the Eyes of Thousands ! 
 
 Several Young Ladies, of only about 25 
 
 * "The frivolous attention of a quarter of an hour of 
 an Evening, has cost many, the comfortable and p-*-fect 
 use of their Eyes for many years : — the mischief is effected 
 imperceptibly — the consequences are irreparable."— Mr. 
 G. ApAMS on Vision^ 8vo. 1789, p. 98. 
 
48 HINTS TO PERSONS CHOOSINO 
 
 years of Age, have complained to me that 
 they could not work without Spectacles of 30 
 Inches focus — who I found, on inquiry, very 
 justly attributed this premature failure of 
 their Sight to having been obliged frequently 
 to sit up at Needle-work half the Night dur- 
 ing the time they were with Dress-makers. 
 
 Those zvho have any regard for the Eyes of 
 their Children — will make it part of the agree- 
 ment, when they article them to any Business 
 requiring the earnest exertion of their Eyes, 
 that they shall never be required, on any 
 pretence, to use them at latest after J^ine 
 o'clock at Night. 
 
 A friend of the Author, who has passed his 
 GOth year, and has found it necessary to use 
 Spectacles ever since he attained the age at 
 which they are usually wanted ; whose oc- 
 cupations have occasioned his Eyes to be 
 constantly employed on small objects in print, 
 writing, and drawing, by Candlelight as well 
 as in the Day, by careful management, is still 
 enabled to see with Spectacles of the first 
 power, or 36 inches focal length, for common 
 purposes ; — ?*. e. for reading moderately sized 
 prints, and writing in Day-light. 
 
 His practice has been, from the period of 
 
SPECTACLES TO READ WITH. 49 
 
 first using Spectacles, never to employ a 
 hio^ber power than was immediately and ab- 
 solutely wanted for the particular occasion, 
 —.for which purpose he constantly carries 
 with him Two pair of Spectacles; one pair 
 of 36 inches, and another pair of 24 inches 
 focal length ; the two pair put on together, 
 serving him for a magnifying power of 12 in- 
 ches focal length for extraordinary purposes. 
 
 The Two pair of Spectacles are for the 
 convenience of being carried in the pocket : 
 at Home, in his study, he has by him all the 
 gradations of 36, 30, 24, 18, and 12 inches 
 focal length, to be used as required. 
 
 He observes, that immediately after using 
 Spectacles of a high magnifying power, the 
 Sight does not easily accommodate itself to 
 a lower power ; and in such cases, it is ne- 
 cessary to give the Eyes a little time to rest 
 and recover themselves. 
 
 This strain of the Eye, and occasion for 
 Spectacles of a high magnifying power, is 
 particularly found in Mending Pens ;* when 
 the inconvenience of the Eye not readily re- 
 storing itself to the capability of seeing with 
 the ordinary Spectacles is strongly evinced : 
 
 * Those who find the Mending of Pens rather a difficult 
 Job ; I recommend the occasional use of a Steel Pen— 
 aspecidlly when they wish to write very small and neatlv. 
 
 ■5 
 
60 HINTS TO PERSONS CH00SIN(1 
 
 to avoid the distressinginconvenience, he has 
 a sufficient number of Pens,* to prevent the 
 necessity of mending any of them until he 
 has finished writing.— I'his method of using 
 the higher powers when the lower powers 
 will not be soon after wanted, is always a 
 provident procedure. 
 
 There is a convenience in Spectacles of a 
 small power, while they can be used. No 
 object can be distinctly seen through Spec- 
 tacles which magnify very much, beyond 
 their focal length; and in using the high 
 magnifying power of 12 inches focal length, 
 prints and writings to be referred to must be 
 placed wUhin that distance -^^ ^^.y^; but 
 with the smaller power oi 36 inches focal 
 lenp^th such objects may be placed to that 
 greater distance from the Eye for being re- 
 ferred to.t 
 
 Therefore the smaller the power, provided 
 it be sufficient, the niore pleasant and conve- 
 nient will be the Spectacles. 
 
 * Mending Pens^ and all operations requiring the Sight 
 to be in its best condition^ should be attended to early in 
 the Day while the Nerves are brisk, and before the Eyes 
 are fatigued : provided the higher magnifying powers are 
 not wanted for this purpose. 
 
 t This supposes a good light, and the object not very 
 minute : but such as could be distinguished at the same 
 distance by the best eyes without glasses. 
 
SPECTACLES TO READ WITH. 51 
 
 By placing upright against a wall, a paper 
 with moderately large printed letters, such 
 as usually occur in the title-pages of Octavo 
 books, he finds the greatest distance he can 
 distinctly see the letters with a good light, to 
 be the Focal length of the Spectacles. For 
 the usual method of measuring the Focal 
 length of Spectacles — See Chapter XV. 
 
 If any doubt should be entertained of the 
 Two Glasses not being of the same focus, he 
 tries each Glass separately with the same 
 Eye, and the difference is immediately dis- 
 covered. 
 
 Besides the alteration in the convexity of 
 the Eye and the muscular power of contrac- 
 tion and dilatation, Age reduces the vividness 
 of the illumination on the Retina ; in conse- 
 quence of which, although objects may be 
 sufficiently magnified by Spectacles, yet they 
 may be scarcely visible when the light is not 
 very strong : but, on the other hand, a too 
 powerful Li^rht is injurious to the Eye. The 
 Light should therefore be economized for the 
 benefit of the Eye. See Chapter Xlll. 
 
 The Artifiriai Light from CiMullesis rare- 
 ly too strong i but '' the Blaze of Day" is 
 often too intense on white paper, and should 
 be tnoderated by placing the paper so as to 
 reduce the reflection of the rays of light upon 
 
52 HINTS TO PERSONS 
 
 the eye : have enough Light, but no more 
 than is sufficient. 
 
 CHAPTER XL 
 
 HINTS TO PERSONS BEGINNING TO WEAR 
 
 SPECTACLES, 
 AND OF READING LAMPS AND CANDLESTICKS. 
 
 When persons first put on Spectacles, if 
 they have chosen ihem ever so wisely — still, 
 they frequently complain that theii' Eyes feel 
 fatigued, — and sometimes even acl^e, after 
 they have worn them some time, especially 
 by Candlelight. There is no wonder in this 
 — it would only be wonderful if they did not. 
 
 It usually happens, that for some months 
 previous to Persons w^earing Spectacles, their 
 Sight has either been strained and weakened 
 by their trying to see what Nature had de- 
 creed that they should not, — or, their Eyes 
 have been Idle, and unaccustomed to be used 
 much, especially by Candlelight. 
 
 The cause of the Complaint people so often 
 make, that their Eyes very soon tire if they 
 use them at Night, is not, as they seem to 
 suppose, entirely from the inferiority of Ar- 
 tificial Light. 
 
Beginning to wear spectacles. 53 
 
 Mr. Argand's invention gave us all that ^e 
 wanted as far as Quantity of Li<j:ht — and Mr. 
 Deville informs me that the Gas light from 
 the Cocoa Nut Oil has the Quality of Day- 
 light ; and that with it, the difference of the 
 colour of Flowers of Sulphur, and that of 
 Wheat Flour, may be easily distinguished, 
 which it is difficult, if not impossible, to see 
 with any other Artificial Light.* 
 
 There are some perfectly authenticated in- 
 stances of persons possessing the faculty of 
 Sight as to the perception of For^m — who had 
 no sense of Colours — -others who could not 
 distinguish their difference by Candlelight — 
 and one I have met with who by Daylight 
 cannot tell Red from Green — but recovers 
 the power of discerning them correctly by 
 Candlelight. The latter is a very singular 
 anomaly of Vision. 
 
 * " The greatest part of Objects, in Candlelight, are al- 
 ways tinged with a Yellow Red, though we are not sensi- 
 ble thereof; because all the objects in view aie changed in 
 the same propction. But if in the day-time you place 
 Candles in a darkened chamber that every thing therein 
 may be well illuminated, and then retire to another place 
 illumi\iated with the Sun'^s light — the Objects illuminated 
 with Candlelight, when viewed through the door of the 
 room, will appear tinged with a yellow red, when compar- 
 ed w'th tho.-e that are seen at the same time illustiated 
 with Day light. "—Dr. PoRTJERFIJBLD on the Eye^ 8vo, 
 1759, Vol. I. p. 127. 
 
54 ' THE CUMUMBRA LAMP* 
 
 THE 
 
 CUMUMBRA & SEMIUMBRA LAMPS, 
 
 Made at Devili^e's Manufactory^ near Exeter 
 ^Change^ Strand. 
 
 The shade of this Laoip is so contrived 
 that it completely prevents any of its rays 
 coming to the Eyes — the pupil of which is 
 therefore regulated solely by the object un- 
 der examination. Every part of the Frame, 
 &c. is coloured a dead black. 
 
 The faults of all the other Reading Lamps 
 which I have seen, are, that the shade does 
 not come either high or low enough to com- 
 pletely shade the light — and at the top is 
 partly composed of fretwork which shows the 
 light through it — ^and the frames are fre- 
 quently painted with a light colour, and high- 
 ly varnished. 
 
 To this Lamp may also be fixed a Half 
 shade, which will screen the Light from the 
 person reading, and at the same time light 
 the Room — which in some cases is a very 
 desirable contrivance. 
 
 It is so simple in its construction, that it is 
 DPt liable to get out of order, and there is 
 very little more trouble in trimming it for 
 
THE CUMUMBRA LAMP. 55 
 
 Seven hours, — than there is in Once snuffing 
 a Candle. 
 
 It is not only cheap in the purchase, but 
 in use, for I think it afford^ more lipbt ^ban 
 Two Candles at the cost of One. The Oil 
 reservoir holds three-fourths of half a pint of 
 Oil, which at the present price of the very 
 best Lamp Oil {5s. 6d. per Gallon,) costs 3 
 pence, which divided by 12, (the number of 
 hours it will burn,) gives the expense of this 
 Light, i. e. A Farthing per Hour. 
 
 The Li^ht of the Cumnmbra is so good, 
 that Persons whose Sight is beginning to fail, 
 and who cannot read by Candlelight with- 
 out Spectacles of 36 inch focus, with this 
 Lamp read as w^ell as they can by Day- 
 light; and so it deserves all the praise which 
 the pickpocket gave to the Gas light — '' It is 
 as bad as Daylight!"— z. e. for Opticians; 
 for by the help of this Lamp persons may 
 read a year or two longer than they would 
 be able to do without — and always, with 
 Glasses of the same magnifying power which 
 they use by Day. 
 
 The effect of a strong Light* I have seen 
 
 * " A person who has been obliged for some years to 
 use Spectacles in reading, will, in the Sunshine, be able 
 to read very easily without them." — Dr. PoRTJBRFIELD 
 on the Eye, 8vo. 1759, Vol. I. p. 162. 
 
56 THE SEMIUMBRA LAMP* 
 
 evidenced by the fact — that Persons who 
 have many years used Spectacles, when the 
 Sun shines on their Book, can see without. 
 
 I believe, that the main Reason why the 
 Sight is not so sharp at J^ight as it is in the 
 Morning, is, that the Eyes are tired, by hav- 
 ing been at work all Day. 
 
 The sensibility of the Sl^hi is surprising- 
 ly recruited by Sleep. Dr. Porterfield, in 
 p. 38 of Vol. II. of his Essay on the Eye, 
 observes, 'Mhe Pupil is very large upon our 
 first awaking.'' 
 
 I have for many years been accustomed 
 to sleep with a light in the Room — and if at 
 any time it has sjone out, I have generally 
 awoke just time enough before to previously 
 light a Candle : and have (^ften wondered, 
 that the diminution of so faint a light had 
 such a strong effect on my Eye, as to awaken 
 me out of a sound Sleep. 
 
 I read the above to Mr. Bundy the Engi- 
 neer, and he said — '' The very same thing 
 happens to me — I always awake just before 
 my Night Lamp goes quite out." 
 
 The best Light for burning all night is the 
 Semiumhra'^ Chamber Lamp, this may be set 
 with perfect security on a Table by the 
 Bedside within reach, and by turning it half 
 
 * Made by Deville, near Exeter 'Change, Strand. 
 
LAMP LIGHT AND CANDLE LIGHT. 57 
 
 round, you may in a moment, have either 
 Light or Shade — a frame may be made to 
 carry it over a Bainmarie Saucepan, like the 
 Nursing Lamps for keeping children's food 
 warm, which will keep half a pint of Tea or 
 Broth warm all Night. This will he a great 
 Comfort to hivolids — especially to those af- 
 flicted with Nii^htmare, for which a draught 
 of hot water will give more immediate, and 
 more permanent relief, than any remedy I 
 have tried. 
 
 See the Author's own Case in pages 20G 
 to 214 of '' The Art of Invigorating Life," 
 4th Edit. 12mo. 1822. Published by Hurst 
 and Co. No. 90, Cheapside. 
 
 The strongest objection to Candlelight is, 
 that the degree of Light given by A Candle^ 
 and its distance from the Eye, is varying 
 every moment; — A Lamp has not this disad- 
 vantage : by merely bringing it nearer to, or 
 removing it farther from the object under 
 examination, its Light may be either increas- 
 ed or diminished, and may be adjusted to 
 almost any degree; and it will continue the 
 same for several hours. 
 
 Those who cannot recollect having played 
 so much with a new Plaything, '' and fancied 
 toil a Pleasure,'' till the pleasure became a 
 Toil,-— must have a much w^orse Memory — 
 than 1 hope you have, gentle Reader ! 
 
I dare say, that " many a time and oft,^^ 
 this has happened to all my Readers, — with 
 much less bewitching Playthings than a pair 
 of Spectacles must at first be to a person 
 who aficr Old Time has for several months 
 interdicted hiui from the amusement of 
 Reading, &c, by this inestimable invention, 
 finds the full enjoyment of his precious Sight 
 - — suddenly and perfectly restored ! 
 
 From one of the causes above mentioned, 
 when persons first put on Spectacles, their 
 Eyes are generally in a state of weakness, if 
 nQ,t of disease: — moreover, at the Age which 
 people usually find their Eyes refuse to be 
 employed on actual service without optical 
 aid be allowed to them, — (which, as I have 
 before said, happens soon after the 40th 
 year), the Visual organs occasionally get 
 out of tune, and participate in that general 
 deterioration of action which every part of 
 our Machinery then begins to suffer. 
 
 Very soon after we pass the Meridian of 
 Life, every Sense becomes duller and weak-^ 
 er, but no one fails so remarkably, as the 
 fine facility of Sight ;•— and although Specta- 
 cles revive the Visual powers ;— they cannot 
 restore to them the untiring energy they 
 possessed in early life. 
 
 Elderly persons can no more play with 
 
WHEN SPECTACLES ARE WANTED. 59 
 
 their Eyes, either so well, or so long, as they 
 did when they were Young— than they can 
 with their Legs and Arms, &c. ! — to expect 
 th^t they can, is about as ridiculous, 'as to 
 suppose thni Infirmity on Crutches, has any 
 chance of rivalling the Champion of Pedes- 
 trians in walking 1000 Miles in 1000 Hours. 
 
 Those who consider these things, will 
 soon cease to be very much surprised, that 
 their Eyes tire sooner at 60 than they did at 
 16 — just in proportion, as all their other 
 faculties become sooner fatigued. 
 
 The effective state of the Eyes, like that 
 of every other part of the Human frame, 
 depends upon that of the Circulation, — which 
 depends upon the condition of the Stomach, 
 and the more or less stimulating Quality, 
 and the Quantity of the material that it is 
 supplied with. 
 
 Several Studious Persons have told me, 
 that their Eyes are never in good order 
 till they have had their Breakfast — that then, 
 they feel as if they were all Head for three 
 or four hours — and then, have as irresistible 
 an inclination for Bodily Exercise, as the^' 
 had previouslj' for Intellectual occupation. 
 
 Over-exercise* of the Eyes, will occasion 
 
 * ^^ The instances of Weakness of Sight which occurred 
 in the early part of my Ophthalmic ^ractice^ were marked. 
 
60 DIMNESS OF SIGHT. 
 
 a temporary exhaustion of them, in like man- 
 ner as over-exercise of the Legs will disable 
 a person from walking with hisw^onted ener- 
 gy — till Rest restores vigour to him, 
 
 I have often heard people complain of 
 their Eyes being out of humour for several 
 days, after beins; exposed lo the glare of the 
 lamps at the Theatre, &:c. — from being fa- 
 tigued by sitting up after their accustomed 
 Hour, — or from other causes which distress- 
 ed their Nervous System. 
 
 When I was 45 years old, I was employed 
 some hours during several Nights, in look- 
 ing intently through Reflecting and Achro- 
 matic Telescopes, endeavouring to ascertain 
 the comparative Illuminating powders of va- 
 rious Instruments, — and the effect of various- 
 ly constructed Magnifiers, for shewing the 
 Division in the Ring of Saturn^ and for sepa- 
 rating some of the faintest and closest Double 
 Stars — my Eye became so extremely tired 
 that the sharpness of my Sight w^as so sensi- 
 bly impaired — that for two or three days 
 after 1 hardly knew any face that was 20 
 
 by great constitutional delicacy, and the individuals had 
 most clearly brought on the Disease, either by excessive 
 attention to jfine dazzling work, or by inordinate indul- 
 gence in literary pursuits protracted frequently to late 
 hours."— -Mr, J. Stevenson on Weakness of Sights Svo., 
 1819. p. 57. 
 
THE POLE STAR. 61 
 
 feet from me, — and became so much alarm- 
 ed, that I mentioned it to an eminent Opti- 
 cian, who said, " Don't be uneasy, the same 
 thing has happeneii more than once to my- 
 self; your Eye has been over- worked — give 
 it a few days' Rest, and I dare say it will 
 soon come round again." — His prediction 
 speedily proved true. 
 
 One of the tests to which 1 put my Eye, 
 and my 5 feet Achromatic, which has a dou- 
 ble object glass of 3/^ aperture, — was, to 
 ascertain with how Low, and how High a 
 power I could see the small Star near the 
 Pole Star: — it was a decidedly detached 
 point of light with a sin2:le eye-glass, which 
 gave the Telescope a power of only 28, i. e. 
 with the 2d E. G. of a compound Astronomi- 
 cal Eye-piece which maejnifies = 44 times — 
 and it was visible with 20 intermediate Eye- 
 tubes, the highest of which magnifies 1386 
 times and is a single Convex lens of the 22d 
 of an inch focus. — The Object Glass being of 
 
 63 Inches focus, 
 gave, multiplied by 22 
 
 the Magnifying Power 1 386 
 6 
 
62 MAGNIFYING POWERS* 
 
 This Instrument is one of the chef-d^cduvres 
 of the late Mr. Peter Dollond— who thus 
 speaks of it to the Gentleman he sold it to, 
 Mr. G. Hodgson, F.R.S., (and of whom I 
 purchased it.) in his Letter, which is now 
 before me, dated Nov. 11, 1803:— "It has 
 been made 10 years, and I can say that it is 
 one of the best I ever made, and such as I 
 cannot expect to be able to equal." 
 
 This 5 feet Telescope literally deserves to 
 be called Achromatic^ for it shews the disk of 
 the Moon and of Jupiter as white and as 
 free from colour as a Reflector ; — to its per- 
 fect Achromaticism I attribute in great mea- 
 sure ils power of very distinctly shewing the 
 division in the Ring of Saturn. 
 
 The visibility of the dark line, which 
 proves the Ring to be double, depends not 
 only upon the distinctness of the image 
 formed by a Telescope,— but on the power 
 it has to shew a white object quite white, 
 and a black one, black. 
 
 When Saturn is near the meridian, the di- 
 vision in its Ring is most plainly visible : 
 but it may generally be observed Two, and 
 in very fine Nights, Three hours, before it 
 comes to the Meridian. 
 
 Those who wish to see this in London, 
 are advised that they will not discern the 
 
DOUBLE RING OP SATURN. G3 
 
 division in the Ring half so well before — as 
 after 10 o'Clock. 
 
 In this " Eljsium of Bricks and Mortar'^ 
 we are so surrounded by "^ Groves of Chim- 
 neys," that until the majority, of the Great 
 Fires of the great Manufactories are out — - 
 the obfuscated atmosphere of this monstrous 
 metropolis defies all the penetrating power 
 that the immortal Herschell himself could 
 bring against it. 
 
 Objects which require all the powers of 
 the Eye to be fresh, and in fine condi- 
 tion, should not be examined when that Or- 
 gan is tired with having been at work all 
 Day. 
 
 If a Planet comes to the Meridian at Mid- 
 night, at 9 or 10 o^Clock lie down in a quiet 
 darkened room, and rest your Eye by get- 
 ting a nap previously. A little Horizontal 
 Refreshment, you will find a proper and 
 renovating preparative for such Contempla- 
 tion; — half-an-hour's Siesta will restore the 
 tone of your Visual Organs, and sharpen 
 your Sight prodio:iously. — 
 
 <«Experto Crede." 
 
 I also saw the small Star near the Polar 
 Star with my Beauclerc Telescope, which 
 has a triple Object glass of 46 inches fo- 
 cus, with a Lens of the 22d of an inch 
 
64 PANCRATIC EYE-TUBE. 
 
 focus, which gave this Glass a power of 
 1012 times. 
 
 This singularly perfect Telescope, which 
 shews Stars as stark neat as ever Nature 
 permitted them to be seen ;- — I purchased at 
 the sale of Mr. Auberfs Instruments, when 
 they were sold at his Observatory, at High- 
 bury Place, by Mr. S. Sotheby, July 24th, 
 1806: — it was originally fitted up for the 
 Honourable Topham Beauclerc^ and Mr. RamS" 
 dmV name is engraven on the Eye-end of 
 the Telescope — but Mr. Peter Dollond in- 
 formed me that he made the Object Glass — 
 and smiling at the time he gave me this 
 information, said, " Yes, that Object Glass 
 is one of the things which is to make me im- 
 mortal," and I then gave him permission to 
 engrave his title thereto on the tube of the 
 Telescope. 
 
 To have produced such a perfect Instru- 
 ment is so honourable to the talent of the 
 artist, that, to avoid all appearance of preju- 
 dice to either of these eminent men, I have 
 called it by the name of the person it was 
 made for, Beauclerc. 
 
 In the Second Part of " The Economy of 
 THE Eyes," which is now preparing for the 
 Press, 
 
 " Paulo majora canamus"— 
 
:^ANCRATIC EYE-TUBE* 63 
 
 the Illuminating and Magnifying Powers of 
 Newtonian, — Gregorian. — Cassegrainian, — 
 Herschelian Reflectors, — and Galilean, — 
 HuGHENiAN and Achromatic Refractina Te- 
 lescopes of various sizes, — will be explained 
 by Experiments made with 46 Telescopes of 
 from 3 Inches to 7 Feet focus, which I pur- 
 chased for that purpose, and have cost me 
 upwards of £1200 ; and which all who have 
 Instruments of the like dimensions, may easily 
 verify at the expense of a few shillings. 
 
 A circumstantial account will be given of 
 their several performances and powers, as 
 Astronomical and Day Telescopes, — being 
 the results of 30 years' observation. 
 
 To enable my Readers to measure the 
 respective merits, and the relative reflective 
 powers of Conrex, — Concave — and Plane Small 
 Specula — I shall lay before them, an abstract 
 of their several pretensions as stated by pre- 
 ceding writers thereon ;— -then proceed with 
 those Practical Observations which I have 
 made myself, and those which I have been 
 favoured with by several scientific Opticians, 
 and amongst them those experienced and 
 excellent M:^kers of Reflecting Telescopes, 
 Messrs. Watson — Tulley — and Cuthbert — 
 who have given me their Notes and Obser- 
 vations thereon, and the account of the Facts 
 6* 
 
GG PANCRATTG EYE-TUBE» 
 
 which they have actually ascertained in the 
 course of their numerous experiments with 
 Telescopes of various constructions. I have 
 only room in this page to add, that the Opi- 
 nions of these eminent Practical Opticians 
 are perfectly unanimous, and in perfect uni- 
 son with those published by Sir !• Newton, — 
 and that 1 believe, that their Evidence and 
 Arguments are so true, and so convincing, 
 and so plainly stated, that they will be per- 
 fectly satisfactory to the Reader, and will 
 finally settle certain important points, which 
 without such Illustration, seem to me, likely 
 to remain as they are at present — 
 
 '' Puzzled with Mazes, and perplexed with Errors." 
 
 I shall also give an account of the inven- 
 tion and advantages of the Pancratic Eye- 
 tube, which to a 3i Achromatic, gives in the 
 most perfect manner every degree of Magni- 
 fying power from 100 to 400 times — which 
 will be minutely described and explained by 
 Engravings. 
 N. B. Contributions on Optical Subjects^ ad" 
 
 dressed to the Publishers of this Work^ will 
 
 be gratefully acknowledged. 
 
 I have mentioned my own case of dimness 
 
 of Sights because, I believe many Artists, 
 
 from the want of such a hint, have greatly 
 
 injured their Eyes, by having been induced 
 
DIMNESS OF SIGHT. 67 
 
 by similar Symptoms, prematurely to put on 
 Spectapcles : but, in such cases, ^^ Rest is the 
 best Remedy." 
 
 " So great is the calamity entailed upon 
 the makers of fine Pieces of Workmanship, 
 such as Clocks and Watches, that many of 
 the Workmen are almost Blind before they 
 arrive at Old Age. I know a Jewish Woman 
 in this City that had a peculiar way of string- 
 ing of Pearls, so as to cover their blemishes 
 if there were any, and by that means got a 
 deal of money; but when she came to be 
 forty years of age, finding no manner of 
 relief from Spectacles, she was forced to 
 leave off the Business. I remember likewise 
 to have heard several Printers complain, that 
 they have given a considerable shock to their 
 Eye-sight by composing small types. 
 
 " In earnest, / do not see how we can afford 
 any Relief to the Workmen zue now treat of; 
 for it is not easy to persuade them to leave 
 a beneficial and lucrative, trade ; aiid Physic 
 is unprovided with any Remedy that can restore 
 the primitive Strength and Mobility of the Eyes^ 
 after the Disorder has become inveterate : for 
 neither Purging, nor Bleedinij, nor other Me- 
 dicinal Means, can take place in this Case, in 
 regard the Patients are otherwise W^ell and 
 Brisk, and their Spirits being neither clouded 
 
68 MAGNIFIEas FOR ARTISTS* 
 
 nor incrassated, it wonld be improper to 
 punish an innocent and sound Head wkh the 
 Commotions of Medicines, 
 
 " However, I would advise such Workmen 
 not only lo fise Speciacles, but. to intermit 
 from thtir Work nozo and then^ and refresh 
 their Eyes by Diversity of Objects. For 
 we can't imagine How much the Mobility of 
 the Membranes of the Eyes, and the native 
 Fluidity of the Humours, is kept up by view- 
 ing divers Objects ; some near at hand, some 
 remote, some directly, others obliquely ; and, 
 in fine, all manner of ways : for by this 
 Means the natural Disposition of the Eye is 
 preserved, so that the Ball is sometimes con- 
 tracted, and sometimes dilated ; and the Crys- 
 talline Humour approaches more or less to 
 the Pupilla, according as the remoteness or 
 nearness of the Object requires. Without 
 this Diversity of Action, the Eyes undergo 
 the same Fate with the other parts, that, by 
 being long detained in one position, grow 
 stiff and unfit for Motion."— Rammazzint on 
 the Diseases of Tradesmen^ chap. xxix. of the 
 Eng. Trans. 8vo. 1705, p. 219. 
 
 Watch-makers, Engravers, and those who 
 are in the habit of using Strong Magnifiers^ 
 would feel their Eyes much less fatigued, if 
 the objects they examine were always placed 
 
MAGNIFIERS FOR ARTISTS. 69 
 
 at once, and kept at the proper focus : — -this 
 might be contrived very easily, by fixing the 
 Magnifying-gU\ss in the opening of a Specta- 
 cle frame, or on a stand, and making a mark 
 where the object of examination is most dis- 
 tinct. 
 
 Nothing can be more detrimental to the 
 organ of sight than the clumsy practice of 
 holding a glass by squeezing the orbicularis 
 muscle^ — this cannot be done without distort- 
 ing, and distressing, and much injuring the 
 mechanism of the Eye. 
 
 The less the Magnifying Power of the 
 Glass, the less the Eye will be fatigued by it, 
 . — the less distressing the position of the 
 Body in working with it, and the larger and 
 more uniformly distinct the field of view : 
 and where a moderate Magnifying: power is 
 sufficient — instead of a single Magnifier, I 
 think it will be better, especially for Etching, 
 and for examining the general Effect of En- 
 graving, &c. to wear Spectacles of 9 inches 
 focus — with which I think that Artists might 
 work longer than with only one Eye. 
 
 The Compound Magnifiers^ which are com- 
 posed of two plano-convexes with their plane 
 sides outwards, are very pleasant — as they 
 have a large and uniformly distinct field. — 
 I have not met with any body who was aware 
 
70 CONCAVES rOH ARTISTS, 
 
 this construction of Eje-glass was invented 
 so long ago as appears by the quotation I 
 here insert :— ■ 
 
 '' Eustachio Divini hath made a Microscope 
 with two piano-convex Glasses, which are so 
 placed as to touch one another in the middle 
 of their convex surface— and hath this pecu-- 
 liar quality, that it shews the object flat and 
 not crooked ; and although it takes in much, 
 yet magnifieth extraordinarily.'' — See PhiL 
 Trans, for 1668, Vol. III. p, 842. 
 
 Concaves which make objects appear the 
 size Artists wish to draw them, are very use- 
 ful to Miniature Painters^ who should have 
 them of two or three different degrees of 
 Concavity— so mounted on a stem that they 
 may be used separately or altogether : thus 
 they may see an object of 6 Feet in diame- 
 ter reduced to exactly the size it is to be deli- 
 neated, i. e. to any degree between 6 Inches 
 in Diameter, and half an inch in Diameter. 
 
 The condition of our Corporeal Machinery, 
 has great influence on that of our Eyes ;•— 
 and indeed of all our Senses.— During that 
 state of collapse which it is just now the 
 fashion to call "a Bilious AltacK^'^—or "a 
 Nervous Paroxysrn^'^— just in proportion that 
 we are out of Heart,™ the Circulation is fee- 
 ble and languid; and every sense performs it^ 
 
DIMNESS OF SIGHT. 71 
 
 functions imperfectly. — During such prostra- 
 tion of the Vital powers, it is not uncommon 
 to hear people complain of Nervous Deaf- 
 ness. — It is equally common for them to be 
 afflicted in an equal degree with Nervous 
 Dimness of Sight. 
 
 This occasional dullness of the Ears, is 
 oftener observed, than the dimness of the 
 Eyes ; — because the former defect is obvious 
 to others, — the latter is confined very much 
 to ourselves; and unless we happen to want 
 to minutely examine some minimum visibile^ 
 which requires all the powers of the Sight to 
 be in full force to be discernible, such a 
 paroxysm of Ocular obtuseness often passes 
 unnoticed, and is seldom strong enough to 
 excite the attention of healthful persons, until 
 they have passed their 40th year; who will 
 then generally find, that it may be traced 
 either to over-exertion of the Eyes, or to 
 some Disorder of the Digestive Organs. 
 
 During derangements of the Restorative 
 Process, for which the Phrase of Fashion 
 now is when you are Nervous or Bilious — 
 the Eye-lids are often affected with " Ophthal- 
 mia Tarsi^^"^ i.e. a slight Inflammation and an 
 increased secretion of the glands about the 
 Eye-lids — which (in plain English) become 
 gummed, and when the Eyes are first opened 
 
72 BAD EYES. 
 
 in the Morning, the Eye-lids feel stiff and 
 the Eyes irritable. 
 
 The Eye-lids^ are much oftener disordered 
 than The Eyes; — perhaps three-fourths of 
 what coninrion people comnaonly call '^ Bad 
 Eyes^^ are merely disease of The Eye-lids. 
 
 I have not space in my little Volume to 
 descant on One of the 118 Principal Disea- 
 ses of the Eye enumerated in the Work of 
 the elaborately minute St. Yves, — but hav- 
 ing had Ocular demonstration of the efficacy 
 and innocence of the following Ointment* for 
 THE Eye-lids — 1 here set it down. 
 
 One part of Citrine Ointment, 
 
 Three of fresh Lard — mix them- thoroughly together 
 with an Ivory knife. 
 
 The Eye-lids are to be anointed with avery 
 
 * *' Whenever I am informed that the edges of the Eye* 
 lids have a disposition, be it ever so slight, to adhere to 
 each other after they have been long in contact, as during 
 the time of sleep, and when this is accompanied with an 
 uncomfortable sense of weight in the lids on the approach 
 of night, in consequence whereof the patient involuntarily 
 shuts them without being drowsy, and without any particu- 
 lar stimulus being applied to the Eye to give it pain, I al- 
 ways suspect that the secretion of the ciliary glands is in 
 a diseased state ; and in many such cases 1 have found the 
 success attending the use of the Unguentum Hydrargyri 
 J^itrati, recommended for the cure of this disorder, quite 
 as effectual as in those other instances, where the excoria- 
 tion and redness of the Eye-lids Jiave been visible on the 
 slightest inspection."— Mr. Ware's Chirurgical Obt, Vol. 
 Lp. 116, 
 
PRECEPTS FOR IMPROVING, &C. 73 
 
 little of this Ointment immediately before go- 
 ing to rest. 
 
 The Eje-Iids should be washed in luke- 
 warm water as soon as you rise in the m.jrn- 
 ing— -and every particle adhering to them, 
 completely, but wevy gently and carefully re- 
 moved — which is easiest done by soaking the 
 Eye-lids by the repeated application of a 
 soft cloth dipped into warm water till what- 
 ever sticks to them is loosened, — then you 
 may proceed cautiously to clean them. 
 
 CHAPTER XII. 
 
 PRECEPTS FOR IMPROVING AND PRESERVING 
 THE SIGHT. 
 
 The Sensibility of the organ of Sights is in 
 proportion to the expansion of the Pupil'^ of the 
 Eye^ whose mean diameter is commonly cal- 
 
 * In the 91st vol. of the Phil. Trans, page 86, in Dr. T. 
 Young's paper on the Mechanism of the Eye — the Dr. has 
 given in Plate v. Fig^ 19, a drawing of ihe front view of 
 his i'ft Eye ; *' when the Pupil is contracted," the diametet* 
 of it IS rather more than a tenth of an inch : and in Fig. 
 20, *' The same view when the Pupil is dilated ;" ihe latter 
 measures almost two tenths and a half. See Copies of 
 these Figures in Plate fronting the Title, Nos. 2 and 3,— 
 in the onenings of the Spectacle frame in the Fvontisniece. 
 7 
 
t4 PRECEPTS FOE IMPROVING AND i 
 
 eulated at about one lOrh of an inch— but 
 varies in magnitude, from One to at least Two 
 tenths, according to the brightness of the ob» 
 ject which is presented to it. — See Dr. FIer- 
 schell's Paper in the Appendix^ 
 
 When the Ligh: is too strong, or the object 
 too bright, the Pupil closes in order to inter- 
 cept that excess of Light* which would oth- 
 erwise offend the Eye: — when the Light is 
 faint, the Pupil expands that a greater quan- 
 tity of it may enter the Eye, and thus make 
 a stronger impression upon it. 
 
 This contraction and dilation of the Pupil, 
 you may easily discern by holding a looking- 
 glass before your Eye at a window and turn- 
 ing gradually round from the window con- 
 tinually looking at your Eye in the looking- 
 glass — the lowest small speculum of a Gre- 
 gorian Telescope, as it magnifies a little, will 
 shew you this still plainer :•— and it may be 
 
 * " 95. The sensibility of the Eye, and its power to dis- 
 cern objects without inconvenience by different quantities 
 of Light is vastly extensive. For instance, the dispropor- 
 tion in the quantities of Light cast upon the horizon By the 
 Sun, and Moon^ at equal altitudes, I find is no less than 
 90,000 — to 1, when the ivlooo is full. 
 
 ^'Day-light is to Moon-Hght as the surface of an Hemi- 
 sphere whose centre is ?t the Eye, to the part of that sur- 
 face which appears to be possessed by the enlightened part 
 of the Moon : so that the whole Heaven? covered with 
 Moons would only make Day-light." — Dr. Smith's Optics^ 
 4to. 1738, p. 29. 
 
PRESERVING THE SIGHT. 75 
 
 easily and perfectly observed by attentively 
 watching the Eye of another, during such a 
 change of position : — it is most visible in a 
 fine full bright blue Eye. 
 
 The fact th; t the sensibility of the Sight* 
 is in proportion to the diameter of the Pupil, 
 is strongly illustrated by the following cir- 
 cumstance.— >' What can be the reason,^' a 
 very intelligent and accurately observing 
 Artist said to me, who was sitting by the side 
 of his window, '^ that w hen I look at that por- 
 trait opposite to me, it looks Warm with my 
 left Eye, and Cold with my Right ; i. e. with 
 my Left Eye, which is from the window, it 
 appears considerably brighter, than it does 
 when I look at it with my Right Eye ?" 
 
 I gave him a '' Circumspector^''^] and desir- 
 
 * We can never be certain that an Object does now 
 appear to us of the same precise Colour of which it appear- 
 ed last Day or last Week : neither can our being insensible 
 to any change ever prove to us that the Colour is the same. 
 Not only different Persons may have different sensations 
 of Colours, proceeding from the different dispositions of 
 their optic nerves and Retinae, or from the different tinc- 
 tures wherewith their Eyes are tinged, but also the same 
 person may, from the same causes, see the same Object, 
 differently coloured at different times without being sensi- 
 ble of it; and experiments are not wanting, whereby it 
 appears, that the same object was seen of different colours, 
 according as it was viewed with the right or left Eye."— 
 Dr. PoRTERFiELD 071 the Eye, 8vo. 1759, Vol. I. p. 128. 
 
 t The CiRCFMSPECTOR, or " Diagonal Eye-glass,^' is 
 a convenient assistant to a Portrait Painter, who wishes 
 
76 I^RECEPTS TOE iSilPROVING A^'& 
 
 ed him to attentively examine the size of the 
 Pupil of each Eye while his head remained 
 in exactly the same position—and tell me in 
 which Eye the Pupil was largest : his answer 
 was, " Why, in the left certainly,'' i. e. in the 
 Eye least exposed to the Light, 
 
 Mr, Butt, of Bath, informed me that he 
 saw the Five first discovered SateUiies of Sa- 
 turn in an Achromatic Telescope of 44 inches 
 focus, and £| inches aperture- — by placing a 
 patch before that part of the field of the Tele- 
 scope where Saturn appeared— and thereby 
 enabling the Pupil to expand, and the Eye to 
 adjust itself for discerning the fainter objects, 
 the Satellites, 
 
 In observing Double Stars^ the very minute 
 Star which accompanies some large Stars, 
 (for instance the small Star near Alpha Lyrw} 
 is visible when the large Star is out of the 
 field^ — with a Telescope with which it is not 
 discernible, while the larger Star is stimula- 
 ting and shutting up the PupiL 
 
 These very striking Facts, sufficiently es- 
 tablish the position laid down in the com- 
 mencement of this Chapter— that " cceteris 
 
 to catch a likeness unobserved, and which is perhaps the 
 only way of obtaining the true natural expression of a 
 Countenance — and is also an invaluable Oracle for a fair 
 Lady to refer to, to adjust the irresistible Artillery of htt 
 Eyes and Smiles. 
 
i^RESERVTNG THE SIGHT. 77 
 
 paribus'''' the iinpre-^sions on the Retina, are 
 vivid, in proportioti to the exparibion of the 
 Pupil. 
 
 These observation?^ led me to consider how 
 beneficial it would be to the Eyes of Paint- 
 ers, Engravers, and those artists whose Eyes 
 are irritable from great exercise, if they could 
 be so shaded, that the Pupil might be secured 
 from being interrupted in its adjustment. 
 For which purpose I recommend a shade 
 made of black silk stiffened with wire, and 
 fixed on a Spectacle frame something like 
 the contrivance of Tubes* which are made 
 for viewing Pictures; such assistance to the 
 Sight — is surely quite as advantageous to the 
 Artist to paint with, as it is to the Amateur 
 to examine his Picture with. 
 
 The Eye cannot adjust itself perfectly, 
 while it is exposed to the stimulus of surround- 
 ing Objects — a defence from the intrusion of 
 collateral rays will prevent the picture on 
 the Retina being confused by those adventi- 
 tious rays which otherwise distract it ; and 
 if only those rays are admitted into the Eye 
 which come direct from the object under ex- 
 
 * See an Account of the great aHvantages of Spect-icles 
 with Leathern Tubes, in the 3d vol. of the Phil, Trans, 
 for the year 1668, p. 727 and 765; aad for 1684 in VoL 
 XIV. p. 474. 
 
 7 ^' 
 
/8 . PRECEPTS TOn IMPFvOTlNfi a:KP 
 
 amination, it will make a much more vivid 
 impression on the Sight, which will be sharp- 
 ened and strengthened very much. 
 
 This is worthy the attention of all who 
 wish their Eyes to enjoy the utmost sensibili- 
 ty that they are capable of being excited to 
 •—because^ 
 
 The action of the Eye is perfect in the pro- 
 portion that its adjustment is perfect — and 
 when all its attention is concentrated on one 
 object, the sensibility of the Sight is much 
 increased ;— moreover, you will not only see 
 better, but Vision being rendered easier, your 
 Eyes may be employed longer, with com- 
 paratively less fati^^ue. 
 
 The Pupil of the Eye is larger when sha- 
 ded by a Broad Brimmed Hat — such as Coach- 
 men w^ear, who probably adopted this cos- 
 tume from its advantage in sharpening their 
 sight. 
 
 There is no part of the Economy of the 
 Eyes more important, than that the object 
 they are at work upon should be placed at 
 exactly that distance from them at which 
 they see with the greatest ease :~this may 
 be easily accomplished by the assistance of 
 
 A DOUBLE-RISIKG DeSK : 
 
PRESERVING THE SIGHT. 
 
 and hard Students will do wisely to have a 
 High Desk at which they can occasionally 
 stand — instead of always sitting. 
 
 Those who are much occupied in Engrav- 
 ing — Painting — Writing— Reading — &c, or 
 works which require all the power of the Eye 
 to be exerted to the utmost — should be care- 
 ful not to offend it by too much Li^ht,, which 
 is quite as prejudicial as too little Light. 
 
 Light enough to illuminate the object, and 
 to make it easily and perfectly visible, is all 
 that is wanted : — on this occasion, the Old 
 Proverb, " Enough is as good as a Feast," 
 is quite true, — more, is not only unnecessary, 
 but injurious, and will not only over-stimulate 
 the Eye — and force the Pupil to shut itself 
 
80 PRECEPTS FOR IMPROVING AND 
 
 up, but if continually so irritated, the Eye 
 will soon become as much impaired by such 
 over-stimulation, as the Stomach is by Dram- 
 drinking. 
 
 1 have observed in my visits to a numer- 
 ously attended Reading Room-— that the seats 
 next the windows were generally filled by 
 persons wearing Spectacles, who had no doubt 
 accelerated the necessity for so doing by a 
 habit of over-stimulating their Eyes with su- 
 perabundant Light. 
 
 The proper way of defending the Eyes from 
 too much Lights is by preventing all that is 
 superfluous from entering the Room, by means 
 of Blinds or Shutters — thus, you may admit 
 only just such a degree of Light as you find 
 most agreeable to your Eyes. 
 
 All Artists choose a Room lighted only from 
 one aperture~^nd if possible with the steady 
 JsTorth aspect ; that is the best place in 
 the room, indeed the only proper place for 
 Study for those who have any regard for 
 their Eyes, where the Light falls on their 
 work or book— coming- from the side or from 
 behind. 
 
 " It is requisite always to have an equal, 
 well regulated Light in every employment^ 
 particularly in the Evening; the Eye may 
 be seriously strained and injured by work» 
 
PRESERVING THE SIGHT. 81 
 
 ing, writing, or reading with either too much 
 or too little Light : for want of a due atten- 
 tion to preserve the visual orfi;an, and irom 
 using the Eyes very much during the busy 
 part of lif^,a morbid sensibility is brought on, 
 an unnatural weight of the Eye-lids, a great 
 deficiency of distmctness, and occasionally 
 a distressing, undulatory quivering appear- 
 ance of refrangible colours on either side. 
 To remedy this, washing the Eyes with clear 
 cold water, and keeping them from the Light 
 for an hour, or taking a Nap, will be found 
 inost efficacious."— S. Pierce. 
 
 If your Eyes are much employed in Read- 
 ing, &C9 and are extremely irritable, you 
 may have your window glazed with Green 
 Glass, — or a bh'nd of it to put up occasionally 
 —or a rolling blind of Green Silk or Muslin 
 — or have a plate of Green glass fixed in a 
 Frame, which may be placed so that the 
 Light may pass through it to your book or 
 work. But do without all these if possible 
 — for if they alleviate the irritation while 
 you use thejo — ihey will render the Eyes 
 more morbidly irrilabie after. 
 
 At Night -use a Reading Candlestick or 
 Lamp with a shade to shield the Eye from 
 the glare of the Light ;* which is of much 
 
 ^ Every thing is best seen when the light of the candle is 
 
82 PRECEPTS FOR IMPROVING AND 
 
 greater assistance to the Sight than those who 
 have not tried it can imagine : One candle so 
 shaded will enable a person to see better 
 than Two without such a shade, and with a 
 Curnumbra Lamp — you may see 1 think al- 
 most quite as well as by Day-light, — the 
 sensibility of the Eye is preserved in such 
 perfection. 
 
 The Optic Pupil inevitably adjusts itself 
 to the brig^htest object, which therefore should 
 be that which it is its business to attend to, — 
 not the flame of a Candle, — but the Book 
 you are reading. 
 
 Green, or any Coloured Glasses, veil ob- 
 jects with a gloomy obscurity, and can never 
 be recommended, except to those who have 
 to travel over a white sand, or are much ex- 
 posed to any bright glare, — which cannot be 
 otherwise moderated. 
 
 Light reflected from any white surface, is 
 very piquant and injurious to the Sight, whe- 
 ther proceeding from Water — Snow, &c. 
 
 Gogglers — or black cups, glassed with plain 
 glasses, and mounted in double-jointed frames 
 formed to the shape of the face— are pre- 
 
 intercepted : the bright light of the Candle not only makes 
 the pupil contract, but by mixing itself with the images of 
 other objects, it in some measure obliterates them, so as 
 they cannot be so well perceived." — Dr. PoRTJBRFIELP Qn 
 the Eye, 8vo. 1759^ VoL 11. p, 188« 
 
PRESERVING THE SIGHT* 83 
 
 ferable to those which are fixed in Leather 
 and Silk and tied on with riband ; the latter 
 come so close to the face that they soon be- 
 come a Vnpour Bath for the Eye—but the 
 former are occasionally found very service- 
 able to travellers to protect their Eyes irom 
 Wind and Dust, and to shield* them from a 
 strong Reflected Light ; Blue or Green glass 
 may be fixed in them, but it must be of a 
 very light Colour. 
 
 Some more nice than wisq folks, among 
 other ridiculous refinements have recom- 
 mended thin Green-Gauze or Crape^ instearl of 
 Green Glass — under the pretence, thai while 
 it moderates the Light, that it still admits the 
 Air, and is, therefore, cooler to the Eyes. 
 
 All Coloured Glasses increase the labour of 
 the Eyes, and soon bring them into such an 
 
 * ** Xenophon relates that many of his Troops were 
 blinded by the strong reflection of the light from the Snow 
 over which they were obliged to march. 
 
 *' Dionysius the Tyrant of Sicily, among other means 
 which he took to gratify his revenge, and satiate ^ he savage 
 cruelty of his Temper, was accustomed to bring fnrth his 
 miserable Captives from the deepest recesses of the darkest 
 Dungeons, into white and well lighted Rooms, th^;t he 
 might blind them by the sudden transition from one extreme 
 to the other. 
 
 " Actuated by principles equally barbarous, the Cartha- 
 ginians cut off the Eye-lids of Regulus and then exposed 
 him to the bright rays of the Sun~by which he was very 
 soon blinded," — G. Adams on Vision, 8vo. 1789, p. 8, 
 
84 PRECEPTS FOR IMPROVING, &C. 
 
 irritable state as unfits them for all the ordi- 
 nary purposes of Life : — there is scarcely 
 an external or internal Sense, but may be 
 brought by extreme indulgence, to such a 
 degree of morbid delicacy and acuteness, as 
 to render tJiose organs which nature intend- 
 ed as sources of gratification-— the frequent 
 sources of Disappointment and Pain. 
 
 The. most proper tnaterial for Spectacle 
 Glasses^ is that which shews objects the near- 
 est to their natural Colour. 
 
 Lastly — Whatever Glasses you use — take 
 care to '^^ keep them perfectly clean :" this is as 
 important, as the choice of the Figure or the 
 Colour of them* 
 
 Every time you wipe your Spectacles you 
 scratch them a little, and " many a little 
 makes a mickle" — therefore, when you have 
 done using them, put them away carefully in 
 their case, to prevent other people abusing 
 theai"-- as a Naughty Boy did his Grand 
 Pa's Spectacles — who took the Glasses out — 
 and when the old Geoiieman put them on- 
 finding that he could not see, exclaimed, 
 '• Marcy me, Pve lost my Sight V — but think- 
 ing the impediment to Vision might be the 
 dirtiness of the Glasses- — took them off to 
 wipe them — when not feeling them, he, stil! 
 
GLASSES, &C, 85 
 
 more frightened, cried out, "Why what's 
 come now, why I've lost my Feeling too !" 
 
 CHAPTER XIII. 
 
 GLASSES FOR SHORT-SIGHTED PERSOiNTS, 
 
 I HAVE met with several persons of 30 and 
 40 years of Age who had no notion that 
 they were Near-sighted, until tljey accident- 
 ally looked through my Speciacles at a dis- 
 tant object ; when thej* exclaiiDed with sur- 
 prise, '' Bless me, how clearly 1 see ! I never 
 saw any Glasses before, that I could see so 
 well with as v/ith my naked Eye, and there- 
 fore had no idea that any Glass could im- 
 prove my sight," 
 
 '^ I can see to read a small print, as well 
 as any body I believe, but I have sometimes 
 suspected that I did not see any thin^ across 
 the street, or at a Theatre, quite ^o plainly 
 as 1 have heard other people say that they 
 did; and I suppose that the Spectacles which 
 I tried before were not suitable to my Sight 
 — and so 1 had no idea that any Glass could 
 improve my Sight." 
 
 For such Eyes I have procured a No. 1, or 
 No. 2, Concave- — and they have been delight- 
 8 
 
SB GLASSES FOR || 
 
 ed — and said, " Well, I see now that 1 have 
 never before discerned the distinct outline of 
 any object which has been further than a few 
 feet from me." 
 
 Being a Short-sighted Uiortal myself, 1 
 write this Chapter with confidence, from my 
 own experience of upwards oi 31 years, and 
 hope to be able to give some good advice to 
 those who are unfortunately what is called 
 JSTear'sighted — by briefly narrating " the His- 
 tory of my ozon Case of Spectacles •'^'^ 
 
 I was about 15 years old, when 1 first dis» 
 covered that I could not discern distant ob« 
 jects so distinctly as people who have com- 
 mon Eyes usually do, 
 
 Mr. Ware, whose pnper on Shortsighted- 
 ness 1 had not seen till after 1 had written 
 this Chapter, has remarked, (see Appendix^ 
 that Young People seldom find out that they 
 are remarkably Short-sighted^ until about the 
 time that 1 did ; which is true, and perhaps 
 for this reason, that Youne Folks seldom at- 
 tend to any thing in earnest before they at- 
 tain to that Age — when seeing, that 1 could 
 not see what persons with common Eyes fre- 
 quently pointed out to me as well deserving 
 my attention, ! paid a visit to ^n Optician and 
 purchased a Concave Eye-glass No. 2. 
 
 After using this some little time, I acci- 
 
SHORT-SIGHTED PERSONS. 87 
 
 dentally looked through a Concave No. 3, and 
 finding my Sight much sharper with this, 
 than with No. 2 — had my Spectacles glassed 
 with No, 3, which appeared to afford my Eye 
 as much assistance as it could receive. 
 
 After using No. 3 for a few Months, I 
 chanced to look through No. 4, and again 
 found the same increase of Sharpness, &c« 
 which i perceived before when I had been 
 using No. 2 and fii'st sav/ through No. S^ — 
 therefore concluded that I had not yet got 
 Glasses sufficiently Concave, and accordingly 
 procured No. 4: — however, this soon became 
 no more stimulus to the Optic Nerve — than 
 its predecessors Nos. 2 and 3 had been. 
 
 I then began to think th>if the Sight is sub* 
 ject to the same laws which govern the other 
 parts of our System ; i. e. an increased Stimu- 
 lus by repetition soon loses its power to pro- 
 duce an increased effect— therefore, I refus- 
 ed my Eye any further assistance than it re- 
 ceived from Spectacles Glassed with No. 2^ 
 which I have worn for upwards of 31 years, 
 and it is very nearly, if not quite, as sufficient 
 help to me now, as it was when I first em- 
 ployed it — giving me a Sight (for objects at 
 a moderate distance,) as I find, by compari- 
 son, about upon i par with common Eyes : — =• 
 without my Spectacles^ I am quite as Short- 
 
88 GLASSES FOE 
 
 sighted as some of my acquaintance who use 
 Nos. 6 and 7 concave ; L e, we read at the 
 same distance. 
 
 Soon after I passed my 40th year I found 
 my Sight become rather S/ior^er as to distant 
 objects — and rather Longer with respect to 
 near objects— formerly, I usually wore Spec- 
 tacles for Readinof, Writing, &c.— -but lately, 
 the power of my Eye to adapt itself to vari- 
 ous distances is so diminished, that when I 
 read, &lc. I am obliged to take off my Glasses 
 —and objects that are more than 70 feet from 
 me, 1 see better with one number deeper than 
 that I commonly wear. — See a similar case 
 in the Appendix. 
 
 The gradations of Concavity, in the Con- 
 caves of the common Spectacles which are 
 marked Cheap in the windows of Sale-shops, 
 ' — Toy-shops, &c.— who pretend to undersell 
 the regular Opticians, (Read Chapter XIX, 
 and See the Appendix,) are not alw^ays work- 
 ed to a certain standard, and what oue per- 
 son calls No. 5, another rates as No. 3, or 4, 
 or 6, or 7. 
 
 Mr. Pierce informed me that the late 
 Mr. Jesse Ramsden made the first No. of his 
 Concaves to be equivalent to a Convex of 24 
 inches focus, — L e. if a Convex of that focal 
 ie*ngth be united to a Concave No. 1— the 
 
SHORT-SIGHTED PERSONS* 89 
 
 eombination will form a Plane, and objects 
 appear through it neither larger nor smaller 
 than they really are. 
 
 A 21 Inch Convex- - - No. 2. 
 
 An 18 Inch No. 3. 
 
 and that all regular Opticians proceed in like 
 manner. 
 
 The following is a very important fact, 
 which the Short-sighted cannot be too fully 
 sensible of: — 
 
 "I shall mention a fact v."'ih which I was 
 made acquaiaied by Mr. George Adams the 
 late Mathematical Instrument Maker, who 
 was not only well skilled in the theory of 
 Vision, but, from his situation as an Artist, 
 had better opportunities than most persons of 
 learning such matters. 
 
 '' The fact is this, that he does not know a 
 Short-sighted Person who has had occasion to 
 increase the depth of his Glasses, if he began 
 to use them in the form of Spectacles ; where* 
 as he can recollect several instances, where 
 those have been obliged to change their Co?i- 
 cave Glasses repeatedly, for others of higher 
 powers, who had been accustomed to apply 
 them to One Eye only.'^'' — Dr. W. C. Wells 
 on Vision, 8vo. 1792, p. 124. 
 
 The advantage of a pair^of Spectacles^ over a 
 Single Glass\ is sufficiently obvious— as Ob- 
 
90 GLASSES FOR 
 
 jects appear brighter when seen with Both 
 Eyes, than they do when viewed with One 
 only. — See Appendix, 
 
 For the Choice of Spectacles for Short- 
 Sighted Persons, — I have few Rules to offer 
 — it is a defect which has no reference to 
 Age— no stated pro2;ression that can be a 
 foundation to guide an Optician, or lead him 
 to recommend one Glass in preference to 
 another — but all depends on the observation 
 of the Short-sighted themselves — who I most 
 earnestly advise, to be content with as Shal- 
 low Concaves as possible— i, e. to take the 
 least Concave Glass through which they can 
 distinctly discern the names on the corners 
 of the Streets, and which gives a decided out- 
 line to objects whose distance does not ex- 
 ceed about 40 feet, and which renders them 
 clear, without making Vision dazzling and 
 glaring — the Glass which does, is too deep 
 by a Number, — See Appendix, 
 
 After your Eyes have been long accusto- 
 med to the assistance of Concave Glasses, the 
 smallest variation in thedeg^ree of their Con- 
 cavity will be extremely distressing and in- 
 jurious to the Sight : — when you have found 
 Glasses which exactly suit you — have Two 
 or Three pairs iitted to your Spectacles, that 
 you may be provided if a Glass gets scratch- 
 ed or broken. 
 
SHORT--SIGHTED PERSONS* 91 
 
 J^ear'S>g;htedness generally continues the 
 same during Life, and precisely the same 
 Glass continues to afford precisely the same 
 assistance. 
 
 After persons have used the same glass for 
 some years — and it is broken, &c, it is often 
 extremely difficult to make them think, that 
 any new one suits their Sight exactly so well 
 as the Old one which they had been in the 
 habit of long using : therefore Pebbles are es- 
 pecially desirable for the Short-sighted. 
 
 Persons who are extremely Short-sighted^ 
 to prevent their stooping in writing- — to read 
 Music, &c. &c. may wear Spectacles with 
 very shallow Concaves, just enough to ena- 
 ble them to «^ee such objects at the same dis- 
 tance which others do. 
 
 A Deeper Concave is wanted to see very 
 Distant Objects. Dr. PvIaskelyne,* the late 
 
 * " When I look at the brighter fixed stars, at consider- 
 able elevations, through a concave glass fitted, as I am 
 short-sighted, to shew them with most distinctness, they 
 appear to me without scintillation, and as a small round 
 circle of fire of a sensible magnitude. If I look at them 
 without the concave glass, or with one not suited to my 
 eye, they appear to cast o'lt rays of a determinate figure 
 not exactly the same in both eyes, somewhpl like branches 
 of trees (which doubtless arise from something in the con- 
 Stru^^tion of the Eye^, and to scintillate a little, if the air 
 be not very clear. To see day objects with most distinct- 
 ness, I require a less concave lens by one degree than for 
 seeing the stars best by night, the cause of which seems to 
 
92 GLASSES FOR 
 
 Astronomer Royal, to look at the Constella- 
 tions, found it convenient to use a Concave 
 one degree deeper than he wore for common 
 purposes in the day time— and the Author 
 uses No, 2. in ordinary, but at Night sees 
 many faint Stars well with No. 3, which he 
 cannot see at all with No. 2. This is espe- 
 cially remarkable in the early part of the 
 Evening when the Stars first become visible* 
 And at Large Theatres^ he finds one Number 
 deeper than that which he ordinarily uses is 
 a very advantageous indulgence to his Eye. 
 
 To give more assistance to the Sight to see a 
 distant object^ mdnj persons hold a Concave 
 Eye-Glass very obliquely so the Ej'C — in 
 which position, a Concave No. 3 will give al- 
 most the same sharpness of outline to objects 
 as No. 3i when held parallel to the Eye. 
 
 For distant Objects, extremely Short- 
 
 be, that the bottom of tbe Eye being illuminated by the 
 day objects, and thereby rendered a light ground, obscures 
 the fainter colours blue, indigo, and violet, in the circle of 
 dissipation, and therefore th^ best image of the object will 
 be found in the focus of the bright yellow rays, and not in 
 that of the vnean refrangible ones, or the dark green, agree- 
 able to Newton's remark, and consequently nearer the re- 
 tina of a short-sighted person ; but the parts of the retina 
 surrounding the circle of dissipntion of a st?y being in the 
 dark, the fainter colours, blue, indigo, and violet, will have 
 some share in forming the image, and consequently the 
 focus Will be shorter."— See PhiL Trans. Vol. LXXIX. 
 
SHORT-SIGHTED PERSONS. 93 
 
 lighted persons should use a small Opera- 
 glass, which having an adjustable focus, if it 
 only magnifies Twice,* will be infinitely bet- 
 ter than any single Concave, because U can 
 be exactly adapted to various distances. 
 
 My • Invisible Opera-Glass ^'^'^ a contrivance 
 of Mr. Pierce and myself, is a great acquisi- 
 tion to Short-sighted Persons, and is an ines- 
 timable little Instrument for Artists, &c. who 
 wish to discern the distinct outline of objects 
 at short inaccessible distances ; i. e. for an 
 Architect to see the exact outline of a Build- 
 ing a furlong off — -or to examine the point- 
 ing, &c. of the walis of upper stories, &c. 
 
 When shut up in its case, this little Glass 
 is only 2 inches in length ; — when in use, 
 about 3 inches : — it has a single plano-convex 
 Object-glass -^^ of an inch in diameter, and 
 its Magnifyirii^ power is about 3 times. 
 
 There is a very general Vulgar Error^ that 
 Short-sighted persons w^ho use Concaves, as 
 they get Older, become less Short-sighted : 
 
 * An Opera-Glas? which only magnifies once, like the 
 fashionable Grand Dandy Ope-as — of which the Eye-glass 
 is as large as the Object-glass — is of no use to a JVear- 
 sighfpd person ; — who, to receive the same benefit which a 
 common Eye does, will require rather more magnifying 
 power : — A very short-sighted person will receive very lit- 
 tle more assistance from an Opera-glass which magnifies 
 Twice, than a person with a Common Eye will from one 
 which magnifies Once, 
 
94 GLASSES FOR 
 
 on the contrary, every Optician and Shori^ 
 sighted person that I have consulted on this 
 subject, have assured me, that as their Eyes 
 become impaired by Age, to see distant ob- 
 jects shnrp and distinct, they require rather 
 deeper than shallower Concaves ; and at a 
 very advanced Age, sometimes complain 
 that they cannot see to read so well as for- 
 merly, and require Convexes of 36 or 30 in- 
 ches focus. 
 
 Mr. Pierce informs me, that Dr. Parker, 
 the late Rector of St. James's, Piccadilly, had 
 from his youth a short-sight, and when al- 
 most four score years of age, complained to 
 him that he could not read so distinctly as 
 he wished : with the help of Convexes of 36 
 inches focus, he was enabled to read and 
 write with comfort to himself for several 
 Years after. — See Appendix. 
 
 That a Short-sight is stronger and better, 
 and more lasting than a Common-sight — I 
 have always set down among the most ab- 
 surd of Vulgar Errors — unless, to be half 
 blind all their Life, as the Short-sighted are, 
 is better than to be so only during about one- 
 third of it, and that during the latter part of 
 Life, as common Eyes are. 
 
 This prejudice is as foolish as the silly nG--^ 
 lion some people have^ — that a severe fit of 
 
SHORT-SIGHTED PERSONS. 95 
 
 Gout, is a thing to give a man Joy of— 
 which our philosophical poet, Pope, admira- 
 bly illustrated when he said : — 
 
 *' So when small humours gather to a Goutj 
 *' The Doctor fancies he has driven them out." 
 
 Lssay on Man, 
 
 If the observations of Lord Chesterfield 
 and Dr. Reid are true, a Short-sighted Per- 
 S071 without Spectacles^ is under a sad disad- 
 vantage in the common business of Life. — 
 The following is the a.dvice this keen obser- 
 ver of Human Nature gave to his Son : — 
 
 " Mind not only WJuU people say, — out 
 How they say it : — if j'ou have any sagacity, 
 you may discover more truth by your Eyes 
 than by your Ears. People can Say what 
 they will, but they cannot Look just as they 
 will ; and their Looks frequently discover 
 what their Words are calculated to conceal.'- 
 — See Letter 77. 
 
 Dr. Thos. Reid's observation on the Eye 
 is — '^ Of the faculties called the Five Stnses^ 
 Sight is, without doubt, the noblest : by 
 means thereof we can perceive the tempers 
 and dispositions, the passions and affections 
 of our fellow-creatures, even when most they 
 want to conceal them : and w^hen the Tongue 
 is taught most artfully to lie and dissemble, 
 the Hypocrisy appears in the countenance 
 
 V 
 
536 SPECTACLE FRAMES. 
 
 to a discerning Eye ! and we can perceive 
 %vhat is straight and what is crooked in the 
 Mind, as well as in the Body." — Inquiry into 
 the Human Mind, 8vo. 1818, p> 140. 
 
 How^ever, it is so^r-e :onsolation to the 
 Short-sighted, to consider, that if the natural 
 infirmity of their Eyes prevent? their enjoy- 
 ing this advantage, the use of Spectacles not 
 only enables them to see what is passing in 
 the Eyes of others, but that they form a veil 
 over their own, which, in a great degree, 
 prevents any such Scrutiny ; and thus — their 
 Weakness becomes their Strength. 
 
 CHAPTER XIV. 
 
 SPECTACLE FRAMES. 
 
 I PREFER a w^ell-hammered Silver Frame 
 with Double Joints, the Second joint of 
 which may be turned on its pin over the 
 First, so that they may be occasionally used 
 with the Single joint only — they sit close and 
 steady on the Head, and c*re convenient to 
 wear under a Hat — do not press either on 
 the Nose or on the Temples — but their pres- 
 sure is general and equal, and as it may be 
 varied, may be rendered more agreeable 
 than any other Frame. 
 
SPECTACLE FRAMES. 97' 
 
 Spectacles with only a Single Joints must 
 press hard somewhere. 
 
 Tortoise-shell Spectacles have a gloomy 
 heavy appearance, are no lighter than Sil- 
 ver ones, and are very easily and very often 
 broken : — however, if you will have a Shell 
 frame, let the front be all Black — variegated 
 Shell is had for the Eye. 
 
 The Blued Steel Frames are good looking 
 enough when new, but soon lose their Azure 
 lustre, and then look very shabby : there is 
 a prejudice in favour of a Steel frame as 
 being very li^ht, — and, from its elasticity, 
 that its pressure on the Head is less than 
 that of a Silver frame. — It may be for the 
 first fortnight; but in the course of that time, 
 such is the ductile nature of a Silver frame^ 
 which soon adapts itself exactly and com- 
 fortabljr to the Head, and becomes infin^'tely 
 easier and pleasanter than the Springy S^ el ; 
 and the truth of the old saying, "• as easy as 
 an Old Shoe," is remarkably felt in " an 
 Old Silver Spectacle Frame." 
 
 That the Frame should be Light, is the 
 only point which either the Makers or the 
 Wearers of it seem to pay any attention to — 
 and to Lightness, every other property of it 
 is willingly, but ridiculously sacrificed. 
 
 The actual difference in Weight between 
 9 
 
98 SPECTACLE FRAMESi 
 
 a Silver Front of that proper decree of 
 strength which I have recommended, and 
 one of the silly jflimsy fronts which are com- 
 monly so much admired, does not exceed 
 Four Penp.y weights 6 
 
 Let the Frame be large enough not to 
 press on the Head, or Head-aches^ <^c* c^c. 
 will be the inevitable consequence* 
 
 The Length of the Bridge, L e. the dis- 
 tance between the Glasses, must be regulated 
 by the distance between the Eyes, and the 
 Centres of the Glasses must come exactly 
 before the Centres of the Eyes ; — according to 
 the coincidence of which, Vision will be 
 perfect or imperfect. 
 
 The mean Distance between the centres of the 
 Pupils of the Eyes of People in general, is 
 about Two Inches and a Half. 
 
 The following are the usual proportions of 
 Spectacle frames. 
 
 The Length of the Bridge^ from an Inch to 
 an Inch and ^^ths. 
 
 Gf the Openings which hold the Glasses, if 
 they are Oval, the longest diameter should 
 not be less than an Inch and jV^h, the Short- 
 est about yVhs* 
 
 The Length of the Common Knuckle is about 
 ^^ths of an Inch :— in some peculiarly formed 
 Faces, this must be wider, and in others nar~ 
 rower. 
 
SPECTACi,E FRAMES. 
 
 99 
 
 The Length of the Knub Knuckle (which is 
 decidedly the most elegant) is only tV^^ ^^ 
 an Inch. 
 
 THE WIDTH OF A COMMON FRAME. 
 
 Bridge 
 
 Openings for the Glasses 
 Rims of ditto . . . , 
 Common Knuckles . , 
 
 In: he 
 
 Tenths 
 
 1 
 
 2 
 
 1 
 4 
 2 
 8 
 
 4 
 
 5 
 
 See Figure in the Plate fronting the Title. 
 
 To assist the Optician to ascertain exactly 
 what ought to be the breadth of the Bridge^ — 1 
 recommend him to have a trial Frame, with 
 an adjusting Bridge which w^ill separate half 
 an Inch — and such separating part graduated 
 1. 2. 3. 4. 5. for each y^^th of an Inch — put 
 these on, and adjust them till the centres of 
 the Glasses come exactly before the centres of 
 the Eyes. 
 
 If his Frames are numbered 1. — 2. — 3. — 
 4. — 5. accpi'ding to the width of the Bridge 
 — the Eyes of his Customers may be imme- 
 diately suited to a nicety. 
 
 The Form of the: Bridge must be regulated 
 by the Form of the Nose which it is to cross. 
 
 The closer the Giasse;- are brought to th^ 
 Eye the better, provided they do not come 
 
100 SPECTACLE FRAMES. 
 
 SO close as to be touched by the Eje-lashes 
 if they do, the Glasses will be continually 
 dimmed by the moisture from the Eye-lash- 
 es ;* and wha. is worse, the Eyelids w^ill 
 bec'-' n uTitated and inflamed. 
 
 in the course of time Spectacle frames get 
 out of prr per shape, and become too looge 
 to keep fhe Glasses up to the Eyes: — this 
 arises so imperceptibly, that I have found it 
 occur to several persons who were uncon- 
 scious of it. — The Optician easily remedies 
 this, by restoring the bend of the Sides to 
 their original form, and new pinning the 
 Joints of them. 
 
 Nothing can look more ridiculous, than the 
 trick which some Idle persons have, of sus- 
 pending their Spectacles on the very tip of 
 their Nose : — this is as injurious to their own 
 Eyes, as it is absurd to the Eyes of others. 
 
 The Bridge of Spectacles for Longsighted 
 Persons^ who wear th^ to read with, is best 
 
 * The quantity of Tears spread over the Globe of each 
 Eye in the space of 24 hours, amounts to Two Ounces and 
 upwards; i> €. a common sized wine-glass full.— People 
 who make use of Spectacles have opportunities of observing, 
 that the evaporation of Tears tarnishes very much the 
 Circles w hich surround the Glasses.- — Dr, P. DegraverSj 
 on the Eye and Ear, 8vo. 1800, p. 116. Surely the subject 
 on which the Doctor made this experiment must have been^ 
 ^qike ^Me all Tears," 
 
SPECTACLE FRAMES. 101 
 
 lof the form, (shewn in the Plate) which when 
 the Eyes are employed in Reading or Work- 
 ing, &c, brings the Glasses parallel to the 
 centres of the Eyes. 
 
 For Short-sighted Persons^ it should be 
 straight — because the Glasses are required 
 to be parallel to the Eyes when you look 
 straight forwards horizontally. 
 
 The proper Shape for the Openings which hold 
 the Glasses^ is the true regular Oval^ — which 
 form is similar to the Opening of the Eye. — ■ 
 The Vulgar opinion is, that Circular Eye 
 Glasses are ground of the most perfect Figure 
 —the Fact is, that the Oval Eye Glasses are 
 ground Round at first and then clipped Oval. 
 
 T%e Front of the Frame should project be- 
 yond the Glasses far enough to protect the 
 GlavSses when people carelessly lay them 
 down on their surfaces-^and also to prevent 
 their being injured by rubbing against the 
 Case, when passing in or out thereof. 
 
 The Front must be Strong enough not to bend 
 in the smallest degree — or the Glasses will lose 
 their parallelism with the Eyes, vision will 
 be distorted, and the Sight distressed. 
 
 * Spectacle frame-makers complain that the Glass grin- 
 ders have a barbarous custom of distorting their Ovals, by 
 putting in ill-shaped Glasses — and forcing the openings to 
 *^d$pt themselves to them. 
 9* 
 
102 SPECTACLE FRAMES, 
 
 The whole of the elasticity of the Frame 
 must be in the sides. 
 
 The First Joint should be of Silver wire of 
 the y^-j-th of an Inch in Diameter, and Four 
 Inches and a half in length, and so curved as 
 not to touch the Head except bj the last half 
 inch of it. The First Joint is seldom more 
 than 4i inches in lensjth— but the apparent- 
 ly trifling addition of a quarter of an Inch in 
 its length gives it a much more steady and 
 comfortable attachment to the Head, than 
 can be imagined by those who have not tried 
 it — -especially when the Second Joint is turn- 
 ed down and you use it with the First Joint 
 only. 
 
 The Second Joint should be flat, about the 
 ■Jth of an Inch in breadth, and 2f Inches in 
 length, with a loop end — and the Pin which 
 fastens it to the First Joint should be kept 
 tight enough to p)reserve the Second Joint in 
 whatever position the wearer finds easiest and 
 most convenient.^ — If this becomes loose — it is 
 easily tightened by placing the pin on which 
 it turns, over a piece of Iron and giving it a 
 gentle tap. 
 
 Mem, — If the Fin which fastens the Second 
 Joint to the First is not rivetted very nicely 
 and smoothly — every time You take off* your 
 Spectacles, you will find it an Infallible De- 
 
SPECTACLE FRAMES. 103 
 
 pilatory — and if ^' Time has not thinnVl your 
 flowing Hair," your Second Joint very soon, 
 will. 
 
 N. B. If the Second Joint be turned up- 
 wards to an x4ngle of about 30 de^>:rees, it 
 will be in the best position for preserving 
 the Frame in its proper place. 
 
 PRICES OF SPECTACLES. 
 
 L, s, d. 
 Best double-jointed silver Spectacles with 
 
 Glasses 110 
 
 Ditto witli Brazil Pebbles ...... 1 16 
 
 Best single joint silver ditto with Glasses . 13 
 
 Ditto with Brazil Pebbles 18 
 
 Double joint Steel ditto with Glasses .,050 
 
 Single joint ditto 036 
 
 Ditto 2 6 
 
 Morocco Cases , 16 
 
 Double-jointed Hand Spectacles in Pearl . 
 
 CHAPTER XV. 
 
 OF THE QUALITY OF SPECTACLE GLASSES, AND 
 HOW TO MEASURE THEIR FOCAL LENGTH. 
 
 The defects of SjKCiacle Glasses are either 
 from Veins — Specks— -Scratches — -Colour— 
 or false Figure. 
 
 1st. To discover Veins in a Convex Glass 
 place a Candle about 5 or 6 yards from you ; 
 then look through the Glass, move it from 
 
i^-^ SPECTACLE GLASSES* 
 
 joirr Eye till you find it full of Light, and 
 you will then clearly see every vein,&c. in it 
 which renders Vision imperfect by distort- 
 ing the Objects. 
 
 2dly. Specks or Scratches are not so mis- 
 chievous as Veins — for they do not distort 
 the object, but only intercept part of the 
 Light ; — ^however, such defective Glasses will 
 not be used, except by such persons who 
 think that their Two Eyes are not worth 
 Two Shillings. 
 
 3dly. False Figure. To prove the Figure, 
 lay a Book before you, hold the Spectacles 
 in your hand, and looking through them re- 
 move them gradually from" the Book. If the 
 figure of the Glasses is false, the objects will 
 appear distorted and confused. Thus if you 
 view any cross lines which form small squares, 
 through a falsely ground glass — some of the 
 squares will appear with strait sides distinct 
 and all of a size ; others with crooked sides 
 of different sizes and confused ; so that the 
 whole will be neither like the original, nor 
 all parts of it distinct at the same distance. 
 
 If you view it through a true glass, it will 
 be exactly like the original figure and uni- 
 formly distinct, only magnified according to 
 the degree of the power of the lens used ; 
 and as you gradually remove the Glass he- 
 
 I 
 
SPECTACLE GLASSES. 105 
 
 yond the focus, if you take care to move the 
 Glass perpendicular to the plane of the Pa- 
 per, all parts of ihe object will become equal- 
 ly indistinrf u the same distance. 
 
 4thly . The Colour of the Glass — That is the 
 best material for looking through, through 
 which Objects appear nearest to their natural 
 Colour — ^(he easiest way of examining the 
 Colour of a Glass is to lay it upon a piece of 
 White Paper. 
 
 To MEASURE THE FoCAL LeNGTH OF SPEC- 
 TACLE Glasses.— The usual manner of mea- 
 suring the focus of Spectacles, is to hold them 
 opposite a window against the side of a room, 
 and draw them gently aw^ay forwards un- 
 til the frame of the window can be seen, 
 making a small image through the Spectacle 
 glass on the Wainscot or Side of the room. 
 When the window frame appears most dis- 
 tinct, the number of inches, measured by a 
 rule betw^een the glass and the wall, or par- 
 tition opposite, will shew the real focal length. 
 
CHAPTER XVI. 
 
 PEBBLES. 
 
 SoiME folks have a notion, that " Pebbles 
 are much cooler to the Eyes than Glasses :"-- - 
 the relationship between " a Pebble" and 
 *' a Stone" and the Proverb " as Cold as a 
 Stone" probably gave rise to this prejudice 
 in favour of Pebbles, 
 
 It is quite impossible to distinguish between 
 good Pebbles and good Glasses. 
 
 People call that Glass coolest to the Eye, 
 which is of the most proper focus for it, and 
 which therefore irritates and fatigues it the 
 least— and through which they can see easi- 
 est and best. 
 
 The only superiority of Pebbles over Glas- 
 ses is, that they are not so liable to be bro- 
 ken ; and as they cannot be scratched by 
 any thing softer than a Diamond^ they may 
 be carried in the pocket without a Case; 
 which are certainly great advantages, espe- 
 cially to Travellers and Short-sighted Per- 
 sons— (See page 100) but I must warn my 
 friend the Reader that Pebbles are so very 
 veiny, that it is seldom a bit is found so per- 
 fect as it ought to be, and therefore I pair of 
 
GBASSES FOB. SPECTACLES* 107 
 
 the Best Pebbles cost 16s. i. e. as much as S 
 pair of the Best Glasses* 
 
 OBSERVATIONS ON THE MATERIALS AND MAN- 
 UFACTURE OF GLASSES FOR SPECTACLES. 
 
 By Mr. S, Pierce, Optician, 
 
 The best material for the formation of 
 Spectacle-giasses^ is the White Plate, common- 
 ly termed Dutch Glass;* it is very clear and 
 hard, without veins or specks comparatively, 
 and bears an excellent polish : Crown-glass 
 is too dark and seedy for the purpose ; 
 French or British Plate is more difficult to 
 polish well, and Spectacle-glasses made there- 
 with are generally Grey ; that is, the fine 
 grinding from the Emery is not sufficiently 
 polished off. 
 
 Much has been said to persuade the Public 
 tW each Spectacle-glass ought to be ground 
 and finished singlj^ by itself, else its defects 
 of variety of foci, incorrect representation of 
 objects, and false colouring, must be consi- 
 derable. But every one acquainted with 
 Glass Grinding, is well convinced, and will 
 
 * I am informed tha* the British Plate Glass now 
 made in East Smithfield, is very superior to any that was 
 formerly made in this country. -^Editor. 
 
108 GLASSES FOR SPECTACLES. 
 
 be ready to assert, that a Glass of so small a 
 diameter as an inch and a half, cannot possi- 
 bly be worked so steadily, nor so true, by the 
 hand singly, nor polished off so fair and re- 
 gular, as when several are worked together 
 in a Block : this block may probably hold 
 four dozen of glasses, which are worked, 
 ground, and polished together in a tool of 
 an exact radius to produce the focal length 
 desired. The firmness of a Block of Glasses 
 secures you against the possibility of form- 
 ing any irregular sphericity, and gives it a 
 decided advantage. 
 
 Some years since. Spectacles were brought 
 from Holland, the glasses of which had been 
 heated sufficiently to receive a Concave or 
 Convex form, by being pressed in iron Pin- 
 cers or Moulds of various curvatures, without 
 any other process: — it is easy to conceive 
 that each Gl?^ss must have had an inequality 
 of/od, extremely injurious to the sight of the 
 unfortunate user, yet these vile glasses were 
 almost universal throughout France and Ger- 
 many. 
 
 In England it is no uncommon thing to find 
 the Spectacle-glasses of an itinerant optician, 
 ground on one side only, while the other side . 
 remains as it was originally cut out from the 
 plate, without being worked at all, and, more- 
 
GF THE EYE AND EAR, lOS 
 
 over, full of veins, &c. which refracting the 
 light irregularly — distort the object and dis- 
 tress and greatly injure the Eye, and are as 
 detrimental to the Eyes as the former ; but 
 the article is sold cheap, w^hich is too often 
 the most tempting recommendation to the 
 million : but as a pair of the very best Glas- 
 ses, which are warranted free from all im- 
 perfections, may be purchased for only two 
 shillings — who would be so mad as to run 
 the risk of forfeiting the fee simple of his 
 precious Sight — for four-and-twenty pence! 
 for a Groat a Year ! ! for the Glasses seldom 
 require changing oftener than or.ce in half-a- 
 dozen years, and sometimes not in a dozen ! ! ! 
 
 CHAPTER XVIL 
 
 ON THE VARIOUS DEGREES OF THE PERFEC- 
 TION OF THE EYE AND EAR. 
 
 Good, and well-educated Eyes are as much 
 delighted with the Harmony of Colours — as 
 fine Ears are with the Harmony oi Sounds 
 — and a cultivated Eye is as much distressed 
 by ill-according Colours — as a cultivated Ear 
 is offended by discordant Sounds. I well re- 
 member that excellent Musician, Dr. Arnold, 
 10 
 
110 VARIOUS DEGREES OF PERFECTION 
 
 telling me when I was studying compositiori 
 with him, that when he first began to learn 
 counterpoint, his Ears were so excruciated 
 bj the Chord of the 2nd of the Key — u e. 
 the Sharp 6th — that he used to call it " the 
 Gritty ChordJ^'^ 
 
 It has been recorded that the Eyes of some 
 persons have been gifted with such Penetrat- 
 ing power (as Dr, Herschel termed what I 
 call Illuminating power) — that they could 
 perceive the Moons of Jupiter. — See G, 
 Adams on Vision^ 8vo, 1789, p. 64, 
 
 I have heard of, but never met with such 
 Visual organs,™ Common Eyes can scarcely 
 perceive them with a good Achromatic Opera 
 Glass magnifying 4 times. 
 
 Father Castel invented an Ocular Harpsi- 
 chord — which was strung with coloured tapes 
 instead of wires, and being placed in a dark 
 room, when the keys were touched, the 
 transparent tapes which corresponded with 
 them became visible. C. published a pam- 
 phlet describing this curious machine, which 
 was translated into English, and I once had 
 a copy of it. 
 
 I have met with some very sensitive Ears 
 — and 1 have known several extraordinary 
 Musicians who have been able, if a handful 
 of the keys of a Harpsichord were put down. 
 
OF THE KYE AND EAR* 111 
 
 SO as to produce the most irrelative combi- 
 nations- — to name each half-note without a 
 mistake. — When I mentioned this to that ex- 
 cellent Organ Player, Mr. Charles Wesley, 
 he said, " At the age of twenty, 1 could do 
 it myself — but I can't now.'' He was then 
 in his 55lh year. 
 
 The delicately discriminatingpower of the 
 Ear is more the gift of Nature than extreme 
 sensibility of the Eye, which latter is I be- 
 lieve always in a considerable degree the re- 
 sult of cultivation. — Miss Cubitt, of the The- 
 atre Royal, Drury Lane, when only six^^years 
 old, surprised me very much, by the high 
 degree she then was gifted with the former 
 faculty ; so was Mr. Watson, of the Theatre 
 Royal, Covent Garden: which they still re- 
 tain. 
 
 Mr. T. Cooke, the Singer and Composer 
 to Drury Lane Theatre, whom no one will 
 contradict me when 1 style the most extra- 
 ordinary Musician of the present Age, when 
 I put down the following Notes on a Piano- 
 Forte,— told me at once, '^ I think. Sir, that 
 you have Beef in one hand— and Cabbage in 
 the other* 
 
112 VARIOys DECREES OF PERFECTION 
 D b Minor, 
 
 B E 
 
 1 
 
 CAB BAGE- 
 
 
 CAB BaG^E,B E E F. 
 
 or G -^ Major. 
 
 Some Eyes are doubtless of as superior a 
 quality as these Ears. 
 
 But the other extreme is more common, of 
 the ears being so dull and badly provided 
 with defining powers, that their owners can 
 hardly distinguish '^ Oh the Roast Beef of 
 Old England*" from ''• Buttered Pease ;'''' — and 
 are more delighted with the discordant 
 screams of kheir Pet Parroquet, the snarling 
 of their Darling Dog--- or some such Barba- 
 rous Uproar — than w^ith the sweetest Melody 
 or the sublimest Harmony — Arne or Handel 
 ever ima2;ined. 
 
 Sound passes through the Paste-board Par- 
 
OF THE EYE AND EAR. 113 
 
 ty Walls of modern houses with such unfor- 
 tunate facility — that the majority of the 
 Dogs — Parrots — Piano-fortes, &c, in this Me- 
 tropolis are — Actionable Nuisances ! ! ! 
 
 1 believe that many of those imperfect per- 
 formances, and erroneous opinions, which are 
 visually ascribed to the want of Skill, or the 
 want of Industry, or Good &7i5e~would be 
 more justly, and will be, set down to the want 
 of Good Senses by those who adjust the Micro- 
 scope of Criticism with Good-nature. 
 
 When I have heard the works of various 
 Artists, of Painters, Enp:ravers, &c. found 
 fault with—for either bad drawing, or bad 
 colouring, or finishing, — 1 have often thought 
 that such defects, in construction or arrange- 
 ment, have been owing more to the Eyes of 
 the Artists not being capable of shewing 
 them how to do better — than to the careless- 
 ness, &c. which they have been inconside- 
 rately censured for those who had a sharper 
 Sight. — A Good Eye, is unhappy, till every 
 part of its work is as perfect as it can make 
 it:— the gratification which it then receives 
 is so superior to all other considerations, that 
 to obtain it—Labour becomes Pleasure. 
 
 We find persons of profoundly Good Sense, 
 have imperfect notions on some subjects, to 
 10* 
 
114 YAEJOUS BEGREES OF PERPECTIOK 
 
 a degree which is quite surprising until ex- 
 plained on these principles. 
 
 Few men are " framed so in the prodigali- 
 ty of Nature,'' as to have all their Senses in 
 perfection— very few have a single One, that 
 approximates within many degrees of it — - 
 the Eye of Raphael^ the Ear of Handel^ — or 
 the sensitive Touch of the Blind Girl who 
 could feel Colours — are pancratic faculties 
 which are seldom produced." 
 
 The peculiar Genius and Character of 
 each Individual originates either in the ex- 
 quisite sensibility — or in the extreme obtuse- 
 ness of some single sense :-— this makes one 
 man a Painter, — another a Musician,-- in op- 
 position to all the influence which can beset 
 tip against it. 
 
 Many eminent Painters and Musicians 
 were originally self-taught, and unable to re- 
 sist the fascination of their Eye or Ear, but 
 were so overcome by their love of their Art 
 — that they have overcome all Obstacles, 
 which were placed in their way to prevent 
 them pursuing it. 
 
 I have met with persons in whom the sense 
 of Seeing or Hearing was so absolutely pre- 
 dominant, that — the other Four appeared to 
 he totally eclipsed : 
 
OF THE EYE AND EAR. 115 
 
 «^ And hence one Master Passion in the breast, 
 Like Aaron's serpent, swallows up the rest." 
 
 Pope. 
 
 Where Nature has given an extremely ^tn- 
 sible faculty to a man, the employment there- 
 of is more delightful and easy to him than 
 the employment of any other, and the culti- 
 vation of it, an irresistible enjoyment. 
 
 This is Genius in ihe proper sense of the 
 ivord, whether in Mind or Body — and is the 
 super-eminent faculty which is born in man. 
 
 The possession of extraordinarily Perfect 
 Senses^ is by no means so enviable as people 
 ordinarily imagine,^ — the works which they 
 enable the possessors to produce can only be 
 fully appreciated by faculties equally perfect 
 and equallj^ cultivated. 
 
 The purblind 
 
 " Undelighted, gaze on all delight," 
 
 The Sagacity to comprehend, and estimate 
 the importance of any uncontemplated im- 
 provement — is confined to the very few, on 
 whom Nature has bestowed a sufficient de- 
 gree of perfection of ihe sense wiiich is to 
 measure it ; — fhe candour to make a fair re- 
 port of it, is still more uncommon — and the 
 kindness to encourage it — cannot often be 
 expected from those, whose most vital inte- 
 rest it is, to prevent the developement of that, 
 "by which their own importance — perhaps 
 
1 1 G VARIOUS DEGREES OP PERFECTION 
 
 their only means of existence — may be for 
 ever eclipsed ; and as Pope says— 
 
 cc ' — How many are 
 
 Condemned in Business or in Arts to drudge 
 Without an Equal — or without a Judge." 
 
 Thus, the Inferiority of the Senses of 
 others — prevents their deriving much advan- 
 tage from the Superiority of their own. 
 
 When Ability and Industry have over- 
 come the difficulties always attending the 
 perfect execution of exquisite works, they 
 have still to contend with the obfuscated 
 imaginations of the Ignorant,-- and the mali- 
 cious misrepresentations of the Idle, — -the In- 
 terested, — and the Envious,— and are seldom 
 repaid for their exertions, unless they are 
 content to reckon with Pope, that 
 
 *' One self-approving hour whole years outweighs 
 Of stupid starers, and of loud huzzas. 
 In parts superior what advantage lies ! 
 Tell, for you can, what is it to be wise ? 
 'Tis but to know who little can be known, 
 To see all other's faults, and feel our own ; 
 Painful pre-eminence yourself to view 
 Above life, weakness, and its comforts too,'* 
 
 Pope. 
 
 Persons who have Bad Senses^ i. e. only 
 just enough Ear and Eye to hear a Dinner 
 Bell, and find a Spoon — often appear to be 
 gifted with Good Sense in a very superior de- 
 gree, and seem to think deeper than those 
 who have the External Senses in greater 
 
OP THE EYE AND EAR. 117 
 
 perfection.— When those avenues to the in- 
 terruption of Intellectual abstraction, the 
 Eyes and Ears, — are half shut, — it is reason- 
 ble to suppose, that the Thinking Faculty 
 may be more active, and more perfect. 
 
 Those persoris vhose External Senses are 
 obtuse and impeiiccL are generally, close 
 Reasoiicrs— subtle Calculdior- — ri^^id Econo- 
 mists, — and ill ail s .• ppcts Persons of exem- 
 plarj^ Pruderice. 
 
 The Insensibility, of people who have Bad 
 Senses^ exempts them from many dive'ting 
 temptations, Vvhich assail those who See — 
 Hear — Feel — Taste — and Smell in perfection. 
 
 That P;!ragon of Good Sense — Dr. S. John- 
 son, was Short sight fd^ and could not see dis- 
 tinctly more than 4 or 5 inches from him. — 
 
 His Ears zvere imperfect also, — when others 
 expressed the delig:Hi they received from Mu- 
 sic, he said, '^ I should he happy to have that 
 sense given to me ;"■— and v hen a celebrated 
 Player had finished -an elaborate Concerto, 
 which they told him was extremely difficult, 
 — he said— '^^ Sir, I wish it had been impos- 
 sible." 
 
 The slovenliness of his own Drr«;s, — 1 dare 
 say arose from the defect in his Sight, pre- 
 venting him from being sensible of ihe agree- 
 able impression produced by proper atten- 
 tion to neatness in others. 
 
il8 PANCRATIC EYE-TUBE. 
 
 We have irresistible evidence that his 
 Taste was defective^ — for his appreciation of 
 a Good Dinner, was according to the Scale 
 which Tasteless people always measure hy^-—- 
 the Variety, the Rarity, and the Costliness of 
 it,— for he needed not Dainties to excite his 
 Appetite ; that, we are told, was sharp enough. 
 
 PANCRATIC EYE-TUBE, 
 
 INVENTED BY 
 
 WILLIAM KITCHINER, M.D. 
 
 Is applicable to Achromatic^ and Reflecting 
 Telescopes of_ all Lengths^ and also to 
 Microscopes. 
 
 [See an Engraving thereof opposite this Page.] 
 
 This Eye- Tube is applied to the Telescope 
 in the same manner as other Eje-tubes, and 
 is adjusted to distinct Vision by the same 
 Pinion Motion. 
 
 * Those in which the Errors arising from Colorific refrac- 
 tion, are corrected by the figure, position, and refractive 
 power of the Lenses which constitute the Object-glas? 
 
 I 
 
a Gem??wrum. W7t7t 2SO. 
 
 iM/'yi/ 
 
 iners Ucorzomy of the Byes j Tart Ipaxje lit 
 
HTi^m (Emmmn^ti^>Mii 
 
PANCRATIC EYE-TUBE, 119 
 
 For the Lowest Magnifying power, the 
 Three Inner lubes must be shut up within 
 the Outer one ;— when the Magnifying power 
 is to be increased, the smallest of the sliding 
 tubes, A, must be draw^n out to either of the 
 numbers engraved upon it ; care being taken 
 not to draw out any part of the other sliding 
 tubes, B and C, until the whole of the Firsts 
 A, is pulled out ; — the Second tube, B, may 
 then be drawn out to either of the numbers 
 engraven thereon ; and in like manner the 
 Third tube. 
 
 The numbers engraved on the Tubes, de- 
 note the Magnifying power of the Telescope. 
 
 To change the Pozver for any less power 
 than the one to which the tubes have been 
 drawn out, the reverse of the above-described 
 mode of proceeding must be observed ; — the 
 Largest tube must be returned first, and so 
 on, until they have been brought back to the 
 number required. 
 
 Each alteration of the Magnifying power will 
 require a new adjustment of the Pinion ;— as 
 the Magnifying power is increased, the dis- 
 tance between the Eye-glass and the Object- 
 glass must be diminished. 
 
 " It has long been known, that the Magni- 
 fying powers of Telescopes could be aug- 
 mented by increasing the distance between 
 
120 PANCRATIC EYE-TUBE. 
 
 the two glasses next to the Eye, and the two 
 that are next to the Object-glass, to almost 
 double the power of the Eye-tube in its usual 
 form, i. e» from 30 to 55. This is the utmost 
 that Opticians have heretofore accomplished ;— 
 yet this variation is so desirable, that I think 
 it only requires to be generally known, to 
 be generally desired, both for Convenience 
 and Cheapness.* 
 
 ^^ A few months ago, I saw an Eye-tube, 
 made by Mr, Cauchoix, with a scale of mag- 
 nifying powers from 25 to 73 ; but, upon 
 trial, I found that the vision was perfectly 
 good only between 35 and 45. 
 
 " My attention was strongly excited by 
 the idea of One Eye-tube effecting the whole 
 business of Magnifying; and after several 
 experiments, with the assistance of Mr. S. 
 Pierce, I combined lenses of such propor- 
 tions that they admitted of being separated 
 from each other so as to Magnify at one ex- 
 tremity, more than double what they did at 
 the other, the vision continuing uniformly 
 distinct. 
 
 * Before Mr. Jesse Ramsden invented, about 1785, 
 The Pipe-draiverfoi- the Terrestrial Eye-tube — and chang- 
 ed the Magnifying power, by chanj2;ingthe two Glasses next 
 to the Eye—for which half Eye-tube he charged 10s, 6d.-— 
 for every change of Magnifying power, there was the in- 
 cumbrance and expense- of another Eye-tubCj costing II. Is. 
 
PANCRATIC EYE-TUBE. 121 
 
 " Having now done more than had been 
 previously effected, I brought it to You. 
 The approbation You expressed of what I 
 had done, so encouraged me, that I applied 
 unceasingly, determined to perfect the object 
 in view, which I have now accomplished, 
 
 " I beg to present to you the following 
 accurate measurement of the powers, and 
 faithful account of the performance of 
 
 " The Pancratic Eye-Tube, which 1 think 
 gives a better defined image of a fixed Star, 
 — and shews Double Stars decidedly more 
 distinct,* and perfectly separated, than any 
 other Eye-tube, and t hope will enable us to 
 determine the distances of these objects from 
 each other, in a mot-e perfect manner than 
 has been possible heretofore.! 
 
 " This Eye-tube, when accurately made, 
 applied to an Achromatic of 44 inches focus, 
 produces, in the most perfect manner, every 
 intermediate degree of Magnifying power 
 between 100 and 400, either for Celestial or 
 
 * Especially in Achromatic Telescopes, which are, what 
 is termed, a little over-corrected, and the purple rays pre- 
 dominate : that is, when the focal length of the Convex 
 Lens, is formed rather too long for the Concave^ 
 
 t This may, perhaps, be accounted for, from the greater 
 degree of the aberration arising from the extreme sphericity 
 of the lenses in other Eye-pieces which magnify so highly, 
 11 
 
122 PANCRATIC EYE-TUBE. 
 
 Terrestrial uses— the Fidd^ of Vision confinU' 
 ing U7iiformly distinct. 
 
 "Therefore it is presumed, that the advan- 
 tage of my Pancratic Eye-tube over the 
 usual common Eye-tube, in variety of Mag- 
 nifying power, — convenience, — cheapness, — 
 and portability, — is as 300 to 1. — The cost 
 of a common Eye-tube is One Pound ; of the 
 Pancratic only Two Pounds, two Shillings. 
 
 " The tubes are graduated ; every 10 de- 
 grees, thus, 100, 110, 120, up to 400. 
 
 '^ The change from one Power to another 
 may be made instantaneously, with the ut- 
 most facility and certainty, and the Observer 
 always knows exactly what Power he is 
 using." 
 
 [The above is an extract from Dr. Kitchi- 
 ner's Letter to Sir Joseph Banks, P.R.S., 
 which was read at the meeting of the R. S. 
 on the 20th of April, 1820.] 
 
 Another is made, which is adapted for 
 Terrestrial purposes, Magnifying with an 
 Achromatic of 44 inches focus, from 55 to 
 
 * It may be said that Common Eye-tubes have rather a 
 larger field — but of what use is that part of the field in 
 which objects appear distorted and fringed with Colour. 
 
 That, can only be considered the actual and useful field 
 of view, the Margin of which, is as perfectly distinct as the 
 middle of the field, when the Telescope is adjusted at aa 
 object seen in the middle of the field. 
 
DAY TELESCOPES. 123 
 
 200 times—and with a 30 inch from 40 to 
 160. 
 
 The power it will give to a Telescope, is 
 according to the focal lensith thereof, and is 
 easily found by the Rule of Three; for in- 
 stance — if the Telescope be of 18 inches 
 focus — 
 
 If a Telescope of) ( what will one of 18 
 44 Inches gives ) ^ ( Inches ? 
 
 18 
 
 44)990(22i the Magnifying 
 88 Power with an 
 
 18 Inch. 
 
 110 
 88 
 
 22 
 from 22i times, up to 88 — being as low a 
 power as is requisite for Land Objects — and 
 as high as is requisite to shew the Ring of 
 Saturn^ — the Belts and Satellites of Jupiter and 
 several Double Stars. 
 
 If the Pancratic be applied to a Telescope 
 with sliding tubes, it is desirable, on account 
 of the great power it produces, that it should 
 
124 DAY TELESCOPES, 
 
 have an Adjusting Screw with a tooth and 
 pinion ; these are made separate from the 
 Telescope, and introduced between the first 
 and second sliding tubes. 
 
 The Advantage— of having All Powers in 
 One Eye-tube is sufficiently obvious. 
 
 In very Clear Days the Air is so transpa- 
 rent, that we can use a Power of 100 for 
 Land Objects, and on objects well illumi- 
 nated sometimes 150, as well as in some other 
 days we can a power of 50. Telescopes 
 act best when used in the same direction that 
 the Sun shines. — I have known good Teles- 
 copes condemned by trying them upon ob- 
 jects situated towards the East in the morn- 
 ing, or the West in the evening. 
 
 To have Perfect Vision— every Day, and 
 every Object, must have its appropriate de- 
 gree of Magnifying* power! — this can only 
 be accomplished by the Pancratia Eye-tube. 
 
 On the 25th of March, 1819, Mr. Pierce, 
 the Optician, with a Pancratic Eye-tube 
 which made a 1 foot Achromatic magnify 
 80 times, perceived a Geminorum to be 
 double. 
 
 * " The Effective Power of Telescopes has a 
 considerable range of extent,— and can only be assigned— » 
 when the Object to be viewed is given." — Sir Wm, HuR- 
 scHELj in Vol, CV. of the PhiL Trans, page 294, 
 
0OUBLE STARS. 125 
 
 On the 5th of April, 1819, 1 shewed this 
 with a power of 70 to Mr. Wrn. Brockedon, 
 the Painter, and to Mr. Charles Turner, the 
 Mezzotinto Engraver in Ordinary to His 
 Majesty. 
 
 ct Geminorum requires very little Ilhimi- 
 nating Power : I have shewn it to several 
 persons who did not know that it was a Dou- 
 ble star, with two 1 foot portable Telescopes, 
 with an Object-glass of the usual aperture of 
 li inch in diameter, to which 1 applied a 
 Pancratic Eye-tube, which gave a power of 
 70 times, and they described to me its 
 appearance very accurately. 
 
 I have seen these two Stars with 230 in an 
 Achromatic Telescope of 28 inches focus, 
 and 2i inches aperture, (which was made by 
 the present Mr. DoUond for the late Mr. G. 
 Hodgson, at whose sale in February last I 
 purchased it,) like Two Shillings on a bit of 
 Black Cloth — See diagram facing page 118; 
 but in which, I beg to observe, that the 
 smaller Star is made rather too small in pro- 
 portion to the larger Star. See Sir Wm. 
 HerschePs diagram of Castor^ as it appeared 
 in his 7 feet Newtonian with 460. in the 
 Phil. Trans, for 1782. 
 
 g Bootis^ was observed on the 25th of May, 
 1819, by Mr. H.Browne, F.R.S. and my- 
 11* 
 
126 DOUBLE STARS. 
 
 self, with an Achromatic Telescope of 2-^ths 
 aperture, made by Mr, George Dollond, 
 F.R.S. With a Pancratic Eye-tube magni- 
 fying 270 the two Stars, were just as per- 
 fectly and as distinctly defined, and at about 
 the distance from each other, as represented 
 in the Engraving of the Pancratic Eye-tube fac- 
 ing page 118, without either rings or raysj 
 &c., around them. This was in an extreme- 
 ly fine clear evening — the air quite still — and 
 the star very near the meridian. The Blue 
 colour of the smaller star was remarkably 
 bright for so small an aperture — This Dou- 
 ble Star is very rarely seen perfectly distinct- 
 ly, in an Achromatic with a less Aperture 
 than 3i, or in a Gregorian Reflector of less 
 than 5 inchfes, and a Power of 300. 
 
 Sir William Herschel saw it in his 7 feet 
 Newtonian when its aperture was limited to 
 Si inches ; with 460 the vacancy between 
 the Stars was i a diameter of the smallest. 
 See Phil. Trans. Vol. 95, p. 42. 
 
 Well might Dr. Maskelyne say that " Te- 
 lescopes of Sir Isaac Kewton^s construction 
 perform most excellently in the Minutim of 
 Astronomy, especially if small Apertures 
 and long Foci are made use of." See 
 Supplement to the Nautical Almanac for 
 1787, p. 42. 
 
DUMPIES. 127 
 
 Magnifying power when required for ohserv- 
 ing Double Stars, is also more perfectly 
 effective in an Achromatic Telescope, in 
 proportion, as it is derived from a prv>per 
 degree of original powei from the Object 
 Glass — the image of the Stars appears small- 
 er, and their separation greater, 
 
 I will here take the liberty to caution 
 those who hereafter may be crazy with the 
 Durapy"^ Mania, that the convenience de- 
 rived from Telescopes being made short, (if 
 beyond a certain proportion,) is greatly more 
 than overbalanced, by the errors produced 
 by the great increase of the aberration of 
 Sphericity arising from the deep curves of 
 the excessively small Eye-glasses we are 
 obliged to employ — there is much difficulty 
 
 * This appellation was first given by Mr. Short, the 
 celebrated Maker of Reflectors, to a Telescope he made 
 for the Honourable Topham Beauclerc, of 6 inches aper- 
 ture, and which I saw in Colonel Auberfs Observatory at 
 Highbury ; it was only 24, instead of the length he usually 
 made them, i. e. 36* inches focus. The instrument is 
 well known in the Optical World by the name of ^' Shorfs 
 Dumpy,^'' 
 
 Mr, Tullty informs me, that this Telescope is still in 
 high preservation, and is now in the possession of Mr» 
 AlleUy Plough Court, Lombard Street. 
 
 * See the Supplement to the Nautical Almanac for 
 1787, p. 39. 
 
128 DUMPIES* 
 
 in getting deep Lenses well worked — and so 
 much more mischievous are the errors aris- 
 ing from any deviation from proper figure. 
 
 It is almost impossible to find an Eye-glass 
 so deep as even the -?^th of an Inch focus, 
 that will give a well-defined image of a Star, 
 notwithstanding much deeper magnifiers are 
 useable in Microscopes. 
 
 Steady Stands are now constructed at a 
 very moderate expense, which make it as 
 easy to use a Telescope of 9 feet, as one of 
 3 feet in length. 
 
 Writing the above, reminds me of a con- 
 versation I had about 25 Years ago with an 
 eminent Optician of great experience:- — 
 
 Kit. How much more convenient short 
 Telescopes are than long ones ! I have late- 
 ly bought a Dumpy. 
 
 Opt. Do you find it perform much better, 
 Sir, than Telescopes which are of the usual 
 length ? 
 
 Kit. No, it certainly does not perform 
 better. . 
 
 Opt. Did you pay much less Money for it 
 then ? 
 
 Kit. No, Sir — -a great deal more. 
 
 Opt. Then 1 think, Sir, that You have laid 
 out your Money very badly — I guess that 
 You have not got so good a Telescope for 
 
DUMPIES* 129 
 
 £30. as You might have had with half the 
 troi-ble to yourself and the Optician for 
 £20. — for You might have had the choice of 
 half a dozen Telescopes of th% usual length, 
 and what does it signify whether the Tube is 
 2 or 4 feet long ? — a Stand that will carry 
 the one will carry the other; and remem- 
 ber, Sir, that Vision is better, and easier to 
 the Eye — in proportion that Magnifying pow- 
 er is produced by Eye-glasses of long foci,-— 
 I am taking it for granted, Sir, that the In- 
 strument is employed for important scientific 
 purposes, when the first consideration is Op- 
 tical perfection. — How^ever, I ask your par- 
 don, Sir, for speaking^ so plainly — perhaps 
 You purchased your Dumpy merely for a 
 Plaything ? 
 
 I have seen e Bootis, as distinctly as re- 
 presented in the diagram, facing page 118, 
 with a Telescope which would not exhibit a 
 glimpse of the small star which accompanies 
 RigeJ^ nor the small star near the Pole Star — 
 and other Telescopes which would plainly 
 shew the latter, but failed entirely at the 
 former. 
 
 Very few Instruments are so perfect, that 
 they will perform perfectly well on all Ob- 
 jects.— There is almost always, some false 
 light flitting about some part of the Image^ 
 
130 DOUBLE STARS. 
 
 and if a small Star happens to be in that 
 part, it is enveloped therein, and is 
 
 " Invisible or dimly seen." 
 
 I do not call it seeing a Star Double, when 
 you can only now and then, fancy you can 
 perceive a faint glimpse of a Utile flitting 
 ghost of an accompanying Star, during fits 
 of easy transmission — l)ut only, when the 
 apparent diameters of the Two Stars are as 
 perfectly round, well defined, and distinctly 
 separate, with a deep black division between 
 them : as they are delineated in the diagrams 
 in the plate facing page 1 1 8. 
 
 I have several times seen that very pretty 
 object, y Andromedod^ with 1-foot Achroma- 
 tics, with an aperture of 1 and -^yh of an 
 inch, and a Magnifying power ot 35. In 
 these little telescopes, the smaller Star which 
 in larger instruments appears of a fine Blue 
 colour — for want of illuminating power, ap» 
 peared of the same colour as the larger 
 Star. Tke Blue Colour of the Stars accom- 
 panying this Star and f Bootis, becomes 
 vivid in proportion to their proximity to the 
 Meridian, and the Perfection and Illuminat- 
 ing power of our Teiescopes. 
 
 i mu^L here caution the Novice, that He 
 must not often expect to see these extremely 
 
DOUBLE STARS. 131 
 
 minute objects to the utmost advantage,* as I 
 have described them, when 1 saw them at 
 very favourable moments with very fine 
 Instruments — especially the Colour of the 
 Blue Stars, even when they are near to the 
 Meridian, and the Illuminating power of the 
 Telescope is in due proportion to the 
 Magnifying power, and the Instrument is Ex- 
 tremely perfect — unless the Air is very clear and 
 still — and every circumstance is favourable,^ 
 
 * "For if there be any vapours iiiovlng and undulating 
 in the atmosphere, which often happens, though tht^ night 
 appenrs clear to the naked eye, these will entirely destroy 
 the distinctness of the appe nance : and it often happens 
 that the air in this respect, at least here with ns at Kew, 
 will so suddenly and so totally alter, that the object will 
 appear very distinct and very confused afterwards in 3 or 
 4 seconds of time ; and the air is sometimes so very varia- 
 ble '"^hat objects will appear instantaneously to change, 
 from being very clear to be confused, and then to be clear 
 again. It will therefore be proper to accustom one's self 
 to the fluctuating appearances of some land-objects, seen 
 in the day time through the reflector ; lest the undulating 
 appearances of the planets in the night may deceive one, 
 and incline one to think this instrument does not succeed 
 so well as it is certain it will in a*pure undisturbed Air." — 
 Dr. Smith's Optics, 4to. vol. ii. p. 366. 
 
 t " I have had recourse to my Journals to find how 
 many Favourable Hours we may Annually hope for in this 
 Climate, 
 
 "It is to be noticed, that the nights must be very clear — ■ 
 the Moon absent — no Twilight — no Haziness — no violent 
 Wind — and no sudden change of Temperature ; — and it ap- 
 pears that a Year which will afford 90, or at most 100 
 Hours, is to be called a very productive one^ ! ! /--Sir Wm. 
 Herschel, in page 84 of "the 90th vol, of the Phil Trans. 
 
132 DOUBLE STARS. 
 
 The Astronomical Amateur should be fully 
 aware, that such is the capricious and vibra- 
 ting state of the Atmosphere of this Country, 
 that many Evenings which seem to be ex- 
 tremely fine, when the Stars appear very 
 brilliant and dazzling to the naked Eye, are 
 quite unfit for Observation, and our best Te- 
 lescopes will perform but very badly. 
 
 Sir Wra. Herschel observes, that '• Double 
 Stars require a great deal of good distinct 
 light ; or even with the best instruments, the 
 observer must not condemn either his instru- 
 ment or his eye if he does not discern them.'' 
 
 N. B. The apparent Diameters — and the 
 Distances of Double Stars^ from each other, — » 
 vary very much, — according to the different 
 states of the Atmosphere, — the Defining,— ^ 
 Illuminating, — and the Magnifying power of 
 the Telescope, and their proximity to the 
 Meridian. 
 
 ^ The Reader will find, in the 26th Number of The Jour- 
 nal of Science^ edited at the Royal Institution, 1822, 24 
 Diagrams of Double Stars, by Mr. J. South, F. R. S. 
 
 fn the Second Part of the Economy of the Eyes — 
 will be given Portraits of the Planets, and Diagrams of the 
 most remarkable Double Stars, as they appear in Tele- 
 scopes of various Magnitudes, with various Magnifying 
 powers — stating with how Low a Power and how Small a 
 Telescope, the Stars may be perceived to be separate, and 
 with What Power they are seen best. 
 
NEWTONIAN DIAGONAL EYE-TUBE. ISS 
 
 To avoid the painful position when observ- 
 ing Celestial objects when they are near the 
 Zenith, I have tried all the 9 different kinds 
 of Diagonal Eye-tubes, the respective advan* 
 tages of which 1 shall state at large in the 
 Second Part of this work ; 1 have only space 
 here to say, that 1 think that the best 1 have 
 was made by Mr. G. DoUond, and consists 
 of a Plane Speculum placed at an angle of 
 45 degrees between the Object Glass and 
 the Eye-glasses, and receives all the Eye- 
 pieces, and renders an Achromatic Refracting 
 Telescope as convenient as a Newtonian Re- 
 flector. 
 
 The light lost in the Reflection is scarcely 
 perceptible when observing fixed stars — the 
 position is not only pleasanter, but our organ 
 of sight is more perfect, when we look com- 
 fortably straight forwards — than it is in the 
 break-neck position required in observing 
 objects in a high Altitude without such as- 
 sistance. It may be urged, that a Prism 
 would bend up the rays with less loss than a 
 Speculum can reflect them — but in the latter 
 you have only one surface to get worked 
 truly, and it is no easy thing to obtain that 
 quite good* — in the former you have several, 
 
 * "I find more difficulty in correcting the figure of the 
 little flain piece of metal next the Eye-glass than one 
 12 
 
134 NEWTONIAN DIAGONAL EYE-TUBE. 
 
 and the imperfections of the glass to contend 
 with into the bargain : — such is the intense 
 intrinsic brightness of the fixed stars, that the 
 inferior degree of vividness of the pencil of 
 rays is, I may say, imperceptible. 
 
 " «ft Lyrae, I surmise, has Light enough to 
 bear being magnified at least a hundred thou- 
 sand times, with no more than 6 inches of 
 aperture, provided we could have such a 
 power, and other considerations would allow 
 us to apply it." 
 
 See Sir Wm. HERScHEt, First Catalogue 
 of Double Stars in the Phil. Trans^ for 1782. 
 
 As Sir Wm. Herschel has remarked, "the 
 Newtonian, as usually constructed, is admi- 
 rably adapted for observation, for the Ob- 
 server always stands erect, and looks in an ho- 
 rizontal direction,though ihe Telescope should 
 be in a vertical position, and elevated to the 
 very Zenith." — 
 
 The position it was placed in by this in- 
 genious Astronomer is, perhaps, still more 
 convenient. 
 
 " My Eye-glass is mounted on that side of 
 
 would expect." — See Sir Isaac JSTewtorCs Letter in the 
 Phil Trans, for 1672, vol. vii. p. 4032 ; and Sir William 
 HerscheVs Obs. in Octob. 12, 1782, in page 44, of the Phil. 
 Trans, for 1 795. — Messrs. Watson and Tulley have assur- 
 ed me that no figure is more difl&cult to make? than a per- 
 fect Plane. 
 
NEWTONIAN DIAGONAL EYE-TUBE. 135 
 
 an octagon tube, which in the horizontal po- 
 sition of the instrument makes an angle of 
 45° with the vertical — having found by ex- 
 perience that this position, resembling the 
 situation of a reading desk, is preferable to 
 the perpendicular one commonly used in the 
 Newtonian construction — which has the capi- 
 tal advantage of rendering observations 
 equally commodious in all altitudes; and 
 you may therefore place the Instrument in 
 the meridian, and view the stars in their most 
 favourable position." — See PhiL Trans, for 
 1786, Vol. Ixxv., p. 457—8. 
 
 I have no hesitation in saying, that in the 
 uncomfortable (and if long continued, pain- 
 ful) position required in observing objects 
 near the Meridian with any other Telescope 
 —no Half Dozen Observers, even if as ex- 
 perienced, and as expert and as indefatigable, 
 as the Immortal Herschel himself, could 
 have performed, what that incomparable Ob- 
 server achieved single-handed with his 1 feet 
 J^eivtonian. 
 
 When we wish to discern those delicate 
 and minute objects, which are the most in- 
 teresting exhibitions our Telescopes display 
 to us, and with the finest Instruments are on- 
 ly discernible with the most favourable cir- 
 cumstances, — we should be in a position of 
 
13G NEWTONrAN DIAGONAL EYE-TUBE. 
 
 the greatest ease : no cramp or painful pos- 
 ture must distort the Body, or irritate the 
 Mind ; — the whole powers of which must be 
 concentrated in the Eye. 
 
 Such is the sympathy between the various 
 organs of the human body, that we may as 
 well attempt to think accurately on two sub- 
 jects at the same time, as to use two Senses 
 at the same moment : — each must be used 
 alone, if we wish to give it a fair chance of 
 doing it^ utmost. — As Skakspeare has observ- 
 ed of Listening with such profound attention, 
 that "rlich other Sense was lost in that of 
 Hearing." 
 
 The Magnitude and Colour^ of Celestial Ob- 
 je^s^ appear surprisingly diff(?rent, to differ- 
 ent Eyes. — The same Evening, that with a 
 power of 180, the planet Jupiter has appear- 
 ed to m.e to be about an Inch and a half in 
 diameter, — a person, who observed it the next 
 minute, said it looked as big as the moon ; — 
 another, about Four inches diameter ; — and a 
 third, thought it did not appear quite so large 
 as a sm^il Pea. 
 
 " It will be necessary here to take notice, 
 that the estimations made with one telescope, 
 cannot be applied to those made with ano- 
 ther. Wh?*tever may be the cause of the 
 apparent diameter of the Stars, they are cer-^ 
 
DOUBLE STARS* 137 
 
 tainly not of equal magnitude with the same 
 powers in different Telescopes, nor of pro-^ 
 portional magnitude with diff'erent powers in 
 the same Telescope."— Sir Wm. Herschel, 
 in vol. 72 of the PhiL Trans. 
 
 N. B. The Reader is cautioned, that my 
 Pancratic Eye-iube^ is composed of Three Inner ^ 
 and an Outer Tube^ and that when all drawn 
 out, it is 14 inches and |rhs in length ; — when 
 shut up, not more than 5i inches ; — and that 
 when drawn out, the magnifying power is 
 Quadruple, what it is when the tubes are 
 shut up. 
 
 As 1 have no Interest in the sale of this 
 Eye-tube, I have stated my opinion upon it 
 — it is made by Mr. Dollond, and sold at 
 £2. 2s. — for £l. Is. more than the common 
 Eye-tubes. 
 
 On the old Plan Two Magnifying powers 
 cost £2. 2s. : with the Pancratic mentioned 
 at page 122, you have Three Hundred for 
 £2. 2s. 
 
 J^one are Genuine but those precisely answer- 
 ing the above description^ and exactly resemble 
 the engraving opposite page 118, and have 
 the following inscription engraven on the 
 Outer Tube :— 
 
 " The Pancratic Eye-tube : Invented by 
 Wm. Kitchiner, M. D." 
 
 1o ^ 
 
138 PANCRATIC EYE-TUBE. 
 
 This remark is necessary, because, Couu" 
 terfeits"^ are made with only One Tube. — which 
 have oniy half the variety of powers the 
 Pancratic has, and consequently, magnify on- 
 ly Half as low — or Half as high as they 
 ought — such are only put to ordinary Tele- 
 scopes, for the reason we have stated, that a 
 low power is pot to an ordinary Opera-glass. 
 
 But the Reader must not expect that every 
 ordinary Telescope which is fitted up mere- 
 ly for Terrestrial purposes, — will properly 
 carry for Celestial purposes, extraordinary 
 high Magnifying Powers, — nothing like it; — 
 nevertheless — such Telescopes may be per- 
 fectly efficient Instruments for the purposes 
 for which they are made, and perform very 
 well for Land Objects — there are plenty of 
 Good Day Telescopes, — but few Superlative 
 Star Telescopes. 
 
 To bear an uncommonly powerful Eye- 
 glass, for Celestial purposes, you must have 
 an uncommor-y perfect Object-glass, and as 
 the difficulty of forming this, increases as 
 the magnifying power to be used with it in- 
 
 * To construct this Eye-tube perfectly, requires AU care 
 and excellent workmanship — the Lenses must be All of ex- 
 actly the right focus — All without any blemish — and the 
 Glasses and the Tubes containing them must be very truly 
 centered with regard to each other, and to the Object Glas?* 
 
DOUBLE STARS. 139 
 
 creases— in like manner, the makers must be 
 rewarded for their trouble, — which is great- 
 er, as the Instrument must be adjusted at a 
 Fixed Star,— which is a much more elabo- 
 rate and Eye-teazing operation than the or- 
 dinary method observed with Day Tele- 
 scopes, of the defining power of which, a 
 Printed Paper is often considered a sufficient 
 criterion. 
 
 If I w^as an Optician, — I think that I would 
 almost as willingly — fValiz blindfold and bare- 
 foot among 9 Red hot Ploughshares laid at 
 unequal distances from each o^Aer,— as have 
 All my Telescopes tried by that truly trou- 
 blesome test a Fixed Star. 
 
 When a Telescope is perfectly adjusted, — 
 a very trifling accident— will derange it so 
 as to prevent its properly defining a Star — 
 although it may not perceptibly affect the 
 brightness or distinctness of the vision of it 
 with any other object — not even w^ith the 
 Planet Jupiter. 
 
 Before You condemn a Telescope because 
 it does not very nicely define a Star, — try it 
 several Evenings with several Eye-pieces, — 
 and let the Maker of it (trust it with no other 
 Person) examine whether it be in perfect Ad- 
 justment. 
 
 Defects in Eye Glassev^ are seldom suspect* 
 
140 PANCRATIC EYE-TUBl!:* 
 
 ed — but, however perfect the original power 
 of the Object Glass or Speculum may be, it 
 will avail little, if one of your Eye Glasses is 
 veiny, &c., or not quite clean— or not exact- 
 ly truly centred to the Object Glass. — Sir 
 Wm. HerschePs Observation in p. 31, of the 
 95th Vol. of the PhiL Trans, is perfectly 
 true :~ 
 
 " The best Eye-lens will give the least spu- 
 rious diameter of a Star." 
 
 Not One Instrument in Tzoenty can be made 
 to give a neat Image of a Star with its w^hole 
 Aperture, — and not 7bo of Them will give 
 quite so perfectly well defined an Image with 
 the Whole Aperture — as when it is to a cer- 
 tain degree contracted. 
 
 I do not think that any Achromatic of 21 
 inches Aperture, and 3i feet focus, can be 
 made to give quite so neat an image of a Star 
 with the w^hole of that Aperture, as a fine 5 
 feet of Sfths Aperture will when it is limited 
 to 21 — I have never seen one that approxi- 
 mated within some degrees of it. 
 
 The more perfect vision in the 5 feet, 
 am aware, is partly to be attributed to thej 
 greater original power of its longer Object! 
 Glass, and to its larger Eye Glasses — but 
 what I have asserted is true of Telescopes of^ 
 
DOUBLE STARS. 
 
 141 
 
 equal length ; though the improvement is not 
 in so high a ratio. 
 
 Whatever inexperienced Amateur Opti- 
 cians may think of this declaration of ^^ the 
 Cook^s Oracle,''^ — 'tis true. 
 
 The Author respectfuUj^ assures the Reader 
 that these Lucubrations from his Garret — are 
 the result of actual experiments; and, like 
 those which were lately published from his 
 Kitchen — are faithful statements of facts re- 
 peatedly proved. 
 
 Although he has been very cautious, in 
 constructing every sentence with words which 
 would express his meaning as exactly and as 
 clearly as He could, — nevertheless, — his 
 chief Ambition has been to give those who 
 may do him the honour of perusing this lit- 
 tle Book, all the Information he has accumu- 
 lated, in the most convincing and most satis- 
 factory manner ;— -and he has never been 
 contented to offer a mere assertion, whenever 
 it has been in his power to produce collate- 
 ral proofs from the writings of experienced 
 authors. 
 
 " If the Aperture of a Telescope be 5 or 6 
 inches, there will be required a piece of Me- 
 tal 7 or 8 inches broad at least, because the 
 figure will scarcely be true to the edges." 
 See Sir Isaac Newton's Letter to the Secre- 
 
142 PANCRATiC EYE-TUBE. 
 
 tary of the Phil Trans. March 26, 1672. vol, 
 vii. p. 4032. 
 
 It may be supposed that Speculums are 
 now worked with more accuracy than when 
 " the Optician's Oracle,*"' Sir I. Newton, wrote 
 the above ; however, I have not yet seen a 
 Reflecting Telescope of 7 Inches Aperture 
 which did not define Stars much better when 
 Jt was contracted in a certain degree. 
 
 That excellent Optician, and candid wri- 
 ter, Mr. Peter Dollond, observes of his Achro- 
 matics, that " though the surfaces of the Con- 
 cave Lens, may be so proportioned as to 
 aberrate exactly equal to the Convex Lens, 
 near the axis, yet as the refractions of the 
 two lenses are not equal, the equality of the 
 aberrations cannot he carried to any great 
 distance from the axis.'' See Mr. Dollond's 
 Letter to Mr. Short in the Phil. Trans, for 
 1765. 
 
 I had an Achromatic of S^^ths Aperture, 
 which was a remarkably brilliant Day Tele- 
 scope, and with which I saw Planets very 
 well- — but could not see Rigd and several 
 other delicate objects distinctly, until its Ob- 
 ject Glass was limited to 2| inches — with 
 3„6„t.hs-— the small Star accompanying Rigel 
 was enveloped in the false light from the 
 large one— with S-f^^^hs inches— it was not 
 
DOUBLE STARS. 143 
 
 much better— but with 2i inches, the little 
 Star was ver}^ distinctly, and easily visible, 
 ' — and it exhibited, 2 Bob'tis — y Leonis^ &c., 
 better than I have generally seen them with 
 Telescopes of 2| inches Aperture. 
 
 Those who have Telescopes which do not 
 define Stars so well as they wish — may, sup- 
 posing the aperture to be 2iths, make a 
 pasteboard cover for the Object end, with an 
 aperture of 2y\ths — and if that be too large, 
 contract it to 2/^ths, and so on by lOths till 
 the Image of a Star is neatly defined. 
 
 The best Advice I can give to Buyers of 
 Telescopes^ is, that — -if they are particular 
 about the Quality of the Instrument, the less 
 curious they are about the Price^ the more 
 likely they are to be pleased with the per- 
 formance of it — if they deal with an Optician 
 of established character, and leave it to his 
 Judgment and Integrity to choose for them — 
 not restraining him in Price — my own expe- 
 rience assures them, they have then, the best 
 chance of obtaining what they desire. 
 
 For instance, a common portable Two feet 
 Achromatic Telescope which is made mere- 
 ly for Day purposes and magnifies about 30 
 times, is sold for £4. 4^. ; — if this is required 
 to carry a power of 100, i e. three times the 
 power it was made to bear ; and to define 
 
144 PANCRATIC EYE-TUBH* 
 
 Double Stars, &c. — it must have a picked 
 Object-glass, — of a degree of perfection, 
 which is only attainable by a casual concur- 
 rence of the various circumstances which 
 combine to form these Compound Object- 
 glasses, 
 
 The Planet Jupiter was till within the last 
 30 years considered the grand test of Tele- 
 scopes for Celestial purposes, — and when it is 
 near to the Meridian it is a pretty severe one — 
 "but many Glasses will define a Printed Pa- 
 per, and shew the Planets very well, w^hich 
 will not so well define Double Stars^ because 
 they were not adjusted at a Star. — Double 
 >Stars were not thought of till the attention of 
 Astronomers was called to them by Sir Wil- 
 liam Herschel publishing his Catalogues in the 
 PhiL Trans, for 1782 and 1785 — since that 
 time, the Art of making Telescopes has been 
 gradually improving, and both the Optical 
 and Mechanical parts of them are now made 
 much more perfect than they were Twenty 
 years ago. 
 
 For exquisite perfection,— we are, in all 
 mechanical matters, almost as much indebt- 
 ed to accident, as to Art : — for instance, a 
 Watch-maker makes a Dozen Chronometers^ 
 and bestows an equal degree of attention to 
 the finishing of each of them ; so much 
 
DOUBLE STARS. 145 
 
 that he has reason to hope they will all per- 
 form equally well : however, — when put to 
 the trial, he commonly finds, that of the 
 Dozen, — perhaps Four^ in spite of all his care 
 and pains, will turn out but indifferent Watch- 
 es, — Six of them good,— and the remaining 
 Two, fine, and fit to 
 
 "Correct Old Time, and regulate the Sun." 
 
 But why Two of his Watches perform with 
 such superior accuracy beyond the others he 
 cannot imagine. 
 
 In every department of Art it is the same, 
 the Acme o/Per/ec^ion is always accidental, — 
 and the most experienced and pains-taking 
 workman cannot attain it with undeviating 
 certainty by any Rules — this Observation 
 applies to a Telescope even more than it does 
 to a Watch — for the Optician has not only to 
 contend with the difficulty of workmanship 
 — but with the greater uncertainty of the 
 quality of the Material he employs ; and if 
 not One in Half a Dozen Chronometers will 
 measure Time truly — not one in a Dozen 
 Telescopes which perform perfectly well for 
 all other purposes, will define Double Stars 
 sharply — and accordingly, those which will, , 
 bear a proportionately High Price. 
 
 Very few persons, however, require Tele- 
 scopes for this purpose. Objects which are 
 13 
 
146 HOW TO ADJUST 
 
 SO severe a test of a Telescope — are as se- 
 vere a trial to the Sight— and those who have 
 due regard for their Eyes, forbear from 
 straining them by all needless exertions. 
 
 See the account of an alarming Dimness of 
 Sights from such fatigue of the Eyq, in pages 
 5d and 60 of this work. 
 
 CHAPTER XVIII. 
 
 OPERA GLASSES. 
 
 ^^ Ne damnent, quae non intelligunt." 
 
 This entertaining Optical Instrument, seems 
 to have escaped the observation of preceding 
 writers on Optics — -the whole, of the ^^ Lex 
 Scripta''' which I have seen about it, is, that 
 ^^ An Opera G/a^s" is like a Galilean Tele- 
 scope, and composed of a concave Eye-glass 
 and a plano-convex Object-glass— and that 
 its Magnifying power will be augmented, in 
 the proportion, that the focal length of the 
 former is diminished, and that of the latter is 
 increased. 
 
 As so little has been written on this sub- 
 ject — I have embraced this opportunity of 
 endeavouring to communicate such informa- 
 tion^as I have collected concerning it. 
 
OPERA GLASSES. 147 
 
 Pew Persons know even 
 
 '' How to Adjust an Opera Glass- — " 
 partly from the want of this knowlege, and 
 partly from the very low Magnifying power, 
 and imperfect consi ruction of Common Opera 
 Glasses— I have not been much surprised, 
 when I have heard people insist, that such 
 Instruments are useless Machines, — which 
 are made merely to be sold. Others, from 
 not knowing how to adjust them, I have heard 
 complain that their Ej^es are always so much 
 strained by looking through them — that they 
 are afraid to use one. 
 
 To look through a Good Opera-Glnss, when 
 it is properly adjusied, — I have not found to 
 be more fatiguing to my own Eye,- — than to 
 look with as earnest attention— at the same 
 Object,-- -for the s;^rae length of time, with 
 my naked Eye. These mi'^takes of Ignorance 
 and Impatience, would not happen so often, 
 if the Instruments were properly construct- 
 ed, and if, in the Case of every Opera Glass^ 
 there were pasted Plain Directions for ad- 
 justing it to Distinct Vision. 
 
 The irritable state of the Eyes, which some 
 Persons complain of, after having passed the 
 evening at a Theatre, is not a mere local af- 
 fection,- — but is to be attributed chiefly, to 
 that general exhaustion of their nervous En- 
 
148 HOW TO ADJUST 
 
 ergy, which many suff'er when they do not 
 retire to rest at their accustomed hour.-- -See 
 pages 58, 59, and 60 of this Volume. 
 
 To give some idea of the Focus^ Opticians 
 sometimes draw a line round the Tube,^ 
 where it is most distinct for a Common Eye 
 at the distance commonly required in our 
 Large Theatres, which, to see the Scenery in 
 perfection^ is seldom less than about 50 or 60 
 feet. 
 
 When You use an Opera G/a55,— hold the 
 Outer tube in one hand, and the Inner with 
 the other hand — and while looking through 
 the Glass at the Object you wish it to shezo you^ 
 ADJUST IT patiently and precisely: — thus,— 
 press the Eye tune towards the Object Glass, 
 Vision will gradually increase in distinctness 
 as the Eye glass approaches its proper dis- 
 tance from the Object glass, and when there^ 
 the Object will be seen perfectly and sharp- 
 ly defined—if the Eye tube be put in be- 
 yond the proper distance,— the object will 
 again become indistinct, and in that casCj 
 
 * As the Reader may have observed, that the Spying 
 Glasses which are in use at Watering Places — and at Sea 
 — have a mark on their tube which is called the place to set 
 it to — very few persons have any idea that every variation 
 in the distance of the Object, or the Age of the person^ 
 requires a variation of the adjustment of the Glass* 
 
OPERA GLASSES. 149 
 
 the Eye tube must be withdrawn again :— a 
 very little practice, will enable a person 
 easily to obtain the precise point at which 
 the most perfect distinctness can be obtain- 
 ed, — This is a much better way of adjusting 
 an Opera Glass — than to put it up to the 
 Eye, and then pull out the Inner tube — by 
 which act, if the tube does not slide regular- 
 ly, or is shorter than you expect, it may 
 suddenly sHp out, and strike your Eye. To 
 prevent this — in the best finished Opera 
 Glasses the end of the inner tube is attach- 
 ed to the outer tube by a spring which 
 screws in. 
 
 The greater the Magnifying power of an 
 Opera Glass, the greater nicety is required 
 in adjusting it. 
 
 If You wish to see any thing 10 or 20 feet 
 further off^ or as much nearer,— for each va- 
 riation of distance, a corresponding varia- 
 tion of Adjustment is required ; i. e. of the 
 distance of the Ocular Glass from the Ob- 
 ject Glass — which must be dimmished, in 
 the proportion that the distance of the Ob- 
 ject is increased. This caution is quite ne- 
 cessary — 1 have met wnth many persons 
 who have condemned an Opera Glass-— be- 
 cause they could only see some objects dis- 
 tinctly with it, and for others they found it 
 13* 
 
160 HOW TO ADJUST 
 
 useless— merely, because they had not been 
 told, thdit— -every variation of the Distance of 
 the Object^ requires a corresponding variation in 
 the Adjustment. More Opera Glasses have 
 been coiidemned for the want of this know- 
 ledge than from any other cause — and more 
 Eye and Object Glasses have been spoiled* 
 Those who are not aware of it — suppose^ 
 that when they turn their Opera Glass to an 
 Object to which it is not adjusted — its 
 Glasses want w-iping, and they keep rub^ 
 bing, til! in a little time they render them 
 about as unfit to look through as Ground 
 Glass. 
 
 To See an Object distinctly at any given 
 distance, The longer and older the Sight of the 
 Person^ the longer the tube must be drawn 
 out — Thus—if a person of 20 years of Age, 
 who has a common Eye^ has adjusted an Ope-^ 
 ra Glass with a power of 4, for distinct 
 vision at the distance of 60 feet — and wishes 
 to set it so that a person of 40 or 50 years 
 of Age, who uses Convex Spectacles of 36 
 or 30 Inches focus, may see as distinctly 
 with it an object at the distance of 60 feet-— 
 he must pull out the tube about the eighth 
 of an Inch further, — more or less, as the 
 Eye is longer or older, and the Magnifying 
 power, and the distance of the Object^ are 
 
OPERA GLASSES. 151 
 
 more or less, — or they must look through 
 the Opera Glass with their Spectacles on. 
 
 Near-sighted People^ when they wear their 
 Spectacles, See at the same focus as persons 
 who have a common eye — wilhout their 
 Spectacles the tube must be pushed in near- 
 er to the Object Giass. 
 
 If an Opera Glass has been kept in a Cold 
 place^ it very commonly happens that soon 
 after a person has taken it from its case, a 
 Mist will spread itself over the Glasses, so 
 as to prevent his distinguishing any Ob- 
 ject. — This, arises from the cold air within 
 the Tubes, becoming condensed on the 
 Glasses, either by the heat of the hand or 
 of the house, — if the Inner tube is draw^n 
 out from the Outer tube, the Mist will pre- 
 sently go off. and the Glasses become quite 
 clear — without any wiping. 
 
 The best way of holding an Opera Glass* 
 
 If you put it up to your Right Eye, hold 
 it wiih your Left Hand— in such a manner, 
 that the Left Arm forms a blind before the 
 Left Eye. 
 
 Some Fidgetty folks, when not looking 
 through their Opera Glass, keep ever and 
 anon, pawing, and wiping the Eye or the Ob- 
 ject Glass ; — neither of these should be 
 touched. — except when it is absolutely ne- 
 
152 OPERA GLASSES* 
 
 cessary to clean them, and then, only with a 
 bit of soft Leather, fine Linen, or the finest 
 Silver Paper. 
 
 The Sliding Tube soon becomes dirtied by 
 the dampness of the hands; — to avoid this, 
 do not touch the Sliding Tuhe^ but take hold 
 only of the Neck of the Eye-head, and ad- 
 just by that. The Sliding tube must be wiped 
 occasionally, and at the same time wipe round 
 the cloth lining of the larger tube — so that it 
 may slide smoothly~if it will move only by 
 fits and st'^rts, you will not be able to adjust 
 it accurately. 
 
 I have heard persons (unacquainted with 
 the Laws of Optics,) complain, that an Opera 
 Glass magnifying 4 times, has not so large a 
 Field of View as a Glass which magnifies 
 only 2 — this cannot be remedied ;-—their 
 only alternative, is to have a small Field 
 distinct, or a large Field of little or no use — 
 with a power of 4 they have in quality, what 
 with 2 they have in quantity, — the objects 
 which they do see, they see much more 
 than twice as distinctly. 
 
 In 1 801 there sprang up " the Grand Dandy 
 Opera Glass^'^'^ with a Great Eye glass ^ as Ugj 
 as its Object glass! — it was imagined, — by 
 the Amateur Optician who introduced it,— 
 that by increasing the diameter of the Eye- 
 
OPERA GLASSES* 16S 
 
 glass, the field of view was proportionately 
 increased, — and that the Stops'^ which had 
 heretofore been plnced as Sentinels to pre- 
 vent the inrusion of false light, — were im- 
 pertinent impediments. 
 
 The fact is.— these great Grand Dandj 
 Eye-glasses, aclualiy magrnfied very little, 
 and on that account had a very large Field 
 • — iioid a Card with an aperture of half an 
 inch in diameter, before the large Eye- 
 glass — you will find the field of View as 
 large, and the Vision as bright through that, 
 as through the Eye-glass of an inch and a 
 half in diameter i — or, apply a Concave of 
 an inch and a half in diameter, which makes 
 
 * These are often opened too Lar^e, especially in Ope- 
 ra Glasses made with a Single Object Glass. — As the Eye^ 
 glass should be a little Larger — so the Stop should be a 
 little (very little) not irore than one-twentieth of an Inch 
 less, than the cone of Bays conning from the Object-glass. 
 
 The effect of the Stop varies according to its distance 
 from the Object-glaFs. 
 
 Tht Diamcttr of the Aperture of the Stop, must bepro^ 
 portioned to the Df-gree of the Maanifying Foiver — the 
 former must be contracted, in proportion that the latter is 
 increased — if it is too large the Vision will be confused and 
 indistinct by the intrusion at False light, if it is too small 
 part of the pencil of rays will be cut off. 
 
 The subject of Stops is excellently illuminated in a 
 Paper on " Indistinctness of Vision," caused by the pre- 
 sence of False Light in Optical Instruments ; and en its 
 Remedies, by C. R. GoRiiVG, IVI.D., in the Journal of 
 Science, No. xxxiii. for April 1824. 
 
154 OPERA GLASSES. 
 
 them magnify 4 times, and you will find that 
 the field of view is not a hair's-breadth wider 
 through that than it is through an Eye-glass 
 of only half an Inch in diameter. 
 
 Vision through the Smaller, is more distinct 
 than through the Larger Eye-glass : — the 
 Eye is apt to wander about before large Eye- 
 glasses, and the margin of the field of view 
 is curved,— Fi^ion is perfectly distinct^ — only^ 
 when you look precisely through the centre of th^ 
 Eye-glass. 
 
 1 shall relate some further Observations, 
 PRO AND CON Concave^ Eye-glasses— when I 
 treat on the comparative Illuminating Pow- 
 ers of Cassegranian, Gregorian, Newtonian, 
 and Achromatic Telescopes in the Second 
 Part of this Work. 
 
 The field of view in Telescopes construct- 
 ed with Convex Eye-glasses, — is regulated, by 
 the Stop which is placed in the focus of the 
 1st Eye-glass, or that next to the Eye; — 
 the diameter of the Stop is regulated by the 
 diaiarler of the 2d Eye-glass, the diameter 
 of which, varies according to the Magnify- 
 ing power used. If the Stop be opened 
 
 * See several Remarks on Concaves in Sir W. Hers« 
 ehel's paper on the Quintuple Belt of the planet Saturn.— 
 Phil Trans, for 1794, vol, Ixxxiv. p. 28; and in vols 
 cv* p. 296» 
 
OPERA GLASSES. 155 
 
 larger than the 2d E. G. it will produce a 
 strong Orange Colour around a very indis- 
 tinct margin — with the same Magnifying power j 
 the field of view is the same^ whether the 
 Aperture of the Telescope be One Inch, or 
 Three. This is easily proved, by contract- 
 ing the Aperture of a Three Inch Telescope 
 to One Inch, when the field of view will re- 
 main the same!i5 — you will find that the only 
 difference in its appearance, is the diminu- 
 tion of the brightness of it. 
 
 But with Perspectives or Galilean Teles- 
 copes, or Opera Glasses which have a Con- 
 cave Eye-glass — The Field of View^ when they 
 do not magnify more than Twice^ depends in a 
 great measure on the Diameter of the Object 
 Glass. 
 
 If an Object Glass of an Inch and a half 
 in diameter, is made to magnify only twice, 
 it will have a much larger field than an 
 Object Glass of an Inch in diameter. 
 
 But when a Magnifying power of 4 times 
 is applied, — an Object Glass of an Inch aper- 
 ture will have very nearly as large a field as 
 one of an Inch and a half— hut through the 
 larger aperture, Objects will appear twice as 
 bright, as they do through the smaller, the 
 Illuminating power of the larger, to the small- 
 er aperture, being as 22 to 10. — These facts 
 
156 OPERA GLASSES. 
 
 any body may prove, by looking through an 
 aperture of an Inch and a half^ and then con- 
 tracting it to an Inch. 
 
 Some of our most valuable discoveries 
 have been purely accidental, — as little the 
 result of scientific investigation, as the Tele- 
 scope, which was found out by Children play- 
 ing with the lenses in a Spectacle-maker's 
 workshop : — these Great Graiid Dandy Eye- 
 glasses, as big as Object Glasses, led me to 
 consider — what Diameter of Eye-glass and 
 Object Glass is actually useful. 
 
 Theoretical Opticians, — have said, — that 
 if the Eye-glass, be as large as the Pupil of 
 the Eye — it will perform as well, as if it was 
 as big as the Dome of St. Paul's. 
 
 The Opening of the Pupil of the Eye is in 
 inverse proportion to the Brightness of the- 
 Objects presented to it — as the latter in- 
 crease in Brightness, the former diminishes 
 in Diameter, therefore — the less the magfti- 
 fying power, the less the Pupil of the Eye — 
 which is always in an inverse proportion to 
 the bigness and brigjhtness of the pencil of 
 Rays from a Telescope. 
 
 The ordinary opening of the Pupil^ when the 
 Eye is turned to the Light, has been com- 
 puted to very little exceed y'^th of an Inch 
 in Diameter ; See Figure 3 in the Engravings 
 
OPERA GLASSES. 157 
 
 fronting the Title, and No. 10 of the Appen- 
 dix. 
 
 Under the idea, that the opening of the 
 Pupil when before an Opera Glass, is of the 
 like dimension, it has been assumed, thai — no 
 matter what be the Magnilying power, or 
 what the Diameter of the Object Glass ol an 
 Opera Glass, an Eje-glass of -/^ths of an Inch 
 in Diameter, would be even larger than is re- 
 quisite. 
 
 My Eye, had for some time suspected the 
 Truth of this Theory : — wishing to avail my- 
 self of the amu ement of a change of Mag- 
 nifying power, and to have an opportunity of 
 illustrating its efl'ects to others, I had a i?e- 
 volving Eye head made like the double Head 
 of the French Opera Glasses, invented by 
 Mr. Cauchoix,* with two Glasses — one mag- 
 
 * I have had three very good Achromatic Opera Glasses 
 made for me by this Optician, of an Inch and a half, — and 
 One of Two Inches apeiture ; but the latter size is heavy, 
 and inconveniently, and I think, uselessly large, — its Dou- 
 ble Object Glass weighs 5 ounces, and the Instrument alto- 
 gether 9 ounces, and cost 5/, in Paris, — See an account of 
 Mr. C'iUCHOix's Opera Glasses, in page 374 of the Edin- 
 burgh Review^ for October, 1819. 
 
 Mem. 1 do not quote this, because I am of the same 
 opinion as the erudite Editor of the pnper referred to — my 
 own opinion of Opera Glasses, is impartially stated^ at the 
 termination of this note. 
 
 Lemiere, JVo. 6 Palais Royal, has introduced an 
 Opera Glass with a Screw adjustmerit, similar to what our 
 14 
 
158 OPERA GLASSES. 
 
 nifying 3, the other 4| 5 the Eye-glasses were 
 y^^ths of an Inch in diameter — and I was sur- 
 prised to find, that on trying an Eye-glass of 
 half an Inch in diameter, Vision was consi- 
 derably brighter and easier to my Eye. 
 
 The Magnifying Power of an Opera GlasSj^ 
 may be varied several different ways : 
 
 ,1st, By having a Concave fixed in the 
 Eye-head which magnifies 2|, |for viewing 
 Pictures, &c. — and another to screw on over 
 that, which will increase the power to 4, for 
 Theatrical purposes ; 
 
 One foot Achromatic Telescopes in a Brass Tube on a 
 Stand have — but the adjustment is so fine, that it is more 
 difficult to find the exact focus with it — than it is by i^oving 
 the Tube, provided that be kept clean and slides smoothly : 
 his charge for an Obera Glass with this adjustment and an 
 Achromatic Object Glass of an Inch and a half in diame- 
 ter, magnifying 2 1-2, is 2/, 4s, 
 
 The machinery foi adjusting the focus, may be as much 
 too fine — as too coarse — The fine Screw adjustment, which 
 stills seems the best that can be applied to Gregorian Re- 
 flectors, was applied to the original 46 Inch Achromatics— 
 but when even a power of 150 is applied to them — it is not 
 quick enough, and the focal point is not half so easily and 
 exactly hit, as with the more modern invention of the Tooth 
 and Pinion adjustment on the side of the Tube, 
 
 I do not mean to insinuate, that I think the productions 
 of our English Opticians are not equal to those of the Pa- 
 risian Artists — I have had several Dozens of Opera Glasses^ 
 made by Mr. Pierce and Mr. Dollond, which are as 
 elegantly formed and finished — and the Optical parts, are 
 as perfect as Art can produce : — For a Description thereof^ 
 see, pp. 153, 154, 156, &c. 
 
OPERA GLASSES. 159 
 
 gdly, By having a Concave fixed in the 
 Eyehead which magnifies 4— -and a Convex 
 to screw on over that, which will reduce the 
 power to 2|-. I like this last plan best, be- 
 cause most light is required for theatrical 
 purposes. The additional Glass may be at- 
 tached to the Eyehead by a hinge on the 
 side ; and when only one of th^ipi is w^anted, 
 the other may be turned up. The opening 
 of the Stop m the Eyehead must be regulat-* 
 ed to suit the deepest power : — or when that 
 is used, a smaller Stop must be brought be- 
 fore the larger one, in the manner in which 
 the Sun Glass is brought before the Eye 
 Glasses in the 4 Eye Glass Perspectives. 
 
 I am induced to offer it as an invariable 
 maxim, — that although there may be no use 
 in the Diameter of the Eye-glass being much 
 larger^ yet, it should be somewhat larger than 
 the Pencil of Rays transmitted by the Object- 
 glass — which, when an Object-glass of 1|- 
 Inch Diameter magnifies 3 times, w^ill, if not 
 cut off by the Stop,* be | an Inch. (See next 
 page.) 
 
 * To ascertain whether any of the O'/ject- Glass is cut off 
 by the Stop in the Eye-tube— 3ic\]ast th-^ Opera Glass to' 
 distinct Vision— then, take out the Eye-glass, put your 
 Finger on the edge of the outside of the Object-glass, and 
 look down the tube-^if you can see your Finger just peep* 
 ing over the edge of the Object-glass— none is cut olt^ 
 
160 OPERA GLASSES. 
 
 As I have before observed, it has been as- 
 sumed that the opening of the pupil of the 
 Eye, when before an Opera Glass, is about 
 YV^h ul an inch in diameter; — 1 believe it 
 ^i es not exceed |-%ths,— -that the Image is 
 brighter with a pencil of three tenths and 
 three quarters than it is with one of three 
 tenths, my Eye assures me is evidently true 
 —but why tne larger pencil of rays makes a 
 stronger impression on the Eye, I will not 
 pretend to offer any reason*— I know, it is 
 contrary to the accepted i he. ry — however, 
 it is True. 
 
 ^« There are more things in Heaven and Earth, Horatio, 
 Than are dreamt of in your Philosophy." 
 
 Shakespeare. 
 
 The Diameter of the Eye-glass, for any 
 Opera Glass, and any Magnifying power — 
 should be rather more than what is given, 
 by reducing the diameier of the Object- 
 glass into Tenths of Inches, and dividing 
 that, by the Magnifying power — 
 
 Thus : for an Object-glass of 1 Inch and 
 a half, — or fifteen lOths in Diameter, — -if a 
 Magnifying power of 4 times he desired, di- 
 vide 15, — the number of Tenths the Object- 
 
 * See Sir Wm, HerscheVs observations on Night GiasseSj 
 in page 68 or 69 oi Vol, 90. of the Phil Trans, 
 
OPERA GLASSES. 161 
 
 glass is in diameter— by 4, the Magnifying 
 power : — 
 
 4)i5(j^^ths and |(hs, the diameter of the 
 12 Pencil of Rays. 
 
 3 
 
 I would hdive the Eye-glass somewhat larger 
 than the Pencil of Rays, i, e. for an OI>ject- 
 glass of -^ inch in diameter, and magnifying 
 4 times, I think that my Eye sees easiest, 
 when the opening of the Aperture in the Eye- 
 head is about fths of an Inch in diameter. 
 
 The Eyehead should be of Black Ivory, 
 not less than an inch and -fths in diameter, 
 and made concave — something in the form of 
 an Eye-bath — or a shade on the side similar to 
 those prefixed to the Tubes used for viewing 
 Pictures — so that it may form a Screen 
 around the Eye, and prevent the intrusion of 
 any rays upon the retina, except those coming 
 directly from the Opera Glass- — this, will not 
 only improve the Vision very much, but also 
 render it much easier to the Eye. {See page 
 78 of this Vol.) 
 
 The average Distance^ at which a Common 
 Eye^ can see distinctly^ the expression of the 
 Human Countenance (in a good light) has 
 been calculated to be about 15 feet. 
 
 The average Distance^ between the Actor and 
 14 * 
 
162 OPERA GLASSES* 
 
 the Spectator^ in the Boxes of a Theatre, is 
 about 4 times 15 feet, i. 6. about 60 feet — - 
 therefore, — to shew distinctly,— an Opera 
 Glass must mngnify 4 times. 
 
 The Bell Operas, which have only one 
 sliding tube, are the best ; in those which 
 have more tubes, the centre of the Object* 
 glass and the centre of the Eye-glass are 
 very seldom exactly opposite to each other 
 —-and in proportion as they are Eccentric, 
 Vision is Imperfect, and the Instrument (ac- 
 cording to a very usual and very useful Op- 
 tical phrase) is said, to be Out of ^icjusU 
 merit. 
 
 Look with a scrutinizing Eye through 
 Operas zvhich are elaborately ornamented and 
 have many Tubes— for it is one of those 
 General Rules which has the fewest excep- 
 tions, that those which are so very pretty to 
 look at, are — not seldom—mere Toys, w^hich 
 are made to be looked at, rather than to be 
 looked through. 
 
 This Caution is quite needful, friendly 
 Reader-- for I think I have been as much 
 puzzled to produce arguments to persuade 
 my friends that Opera Glasses are not always 
 to be chosen for their Tubes, as I have had 
 to assure them that — a Piano-Forte will not 
 always make good its claims^ to lavour from 
 
OPERA GLASSES. 163 
 
 the Ear — exactly in the proportion that its 
 external appearance happens to please the 
 Eye. 
 
 As Ten are mnde of the plain mountings, 
 fo One of the other, it is, in like proportion, 
 easy to pick out a fine one. 
 
 The majority of the Opera Glasses which 
 are sold at Trinket and Toy-shops, magnify 
 so little^ and are of so little use — that many 
 people who have good Eyes, say with truth, 
 that they can see as well with their naked 
 Eye — I have met with many who have said 
 so to me — but, when I have shewed them a 
 good Opera Glass, magnifying 4 times ^precisely 
 tuned to the peculiar pitch of their Visual Organ 
 ' — they have All, acknowleged, with astonish- 
 ment and delight, the surprising aid that their 
 Sight received from the Eye-invigorating 
 power of Optics, which enabled them — to 
 See Persons in the most distant parts of the Thea- 
 tre^ almost as distinctly^ as those zoho were within 
 15 feet. 
 
 After a deliberate, and fair trial of the 
 Magnifying powers of 3 — 4 — 5 — 6, &c., my 
 Verdict is, — that for use in the Theatre, for 
 Common Eyes, a Magnifying power of about 
 4 times ^ is decidedly^ the most generally useful 
 and agreeable^' — and what is of great impor- 
 tance, as the Eye is sometimes before it for 
 
164 OPERA GLASSES* 
 
 a long time, it is — much easier to the Eye than a 
 Higher Power. 
 
 Persons who are extremely Short-sighted^ — 
 (See the Note at the foot of page 93), may 
 find a Concave which produces a power of 
 5 to a common Eye, not too much for them. 
 
 It is desirable, that the Magnifying Power 
 be as Low as can 6e, that the Field of View 
 may be as Large as can be ; because the lat- 
 ter depends party on the former — moreover, 
 the vapour from the breath of a large As- 
 sembly, and the Smoke from the numerous 
 ' Lamps, &c. prevent our using much Magni- 
 fying power. 
 
 When I suggested my opinion of what ought 
 to be the Magnifying power of an Opera Glass 
 to an Optician — I was told, ^Mt has been 
 tried— but the less they magnify, the more 
 people like them ; and indeed, those seem to 
 me to be most approved, which magnify so 
 little that they scarcely require any Adjust- 
 ment." 
 
 Exquisite Opera Glasses^ that have no focus ! 
 — and are equally distinct, whether all the 
 Eye-tube is pulled out, or all put in ! ! — or 
 you put up the Large, or the Small end to 
 your Eye ! I ! — My Optical friend added, with 
 a smile, " You may laugh, Sir, — but every 
 body has not time to listen to a Long Story 
 about — FocuSj — Adjustment, &c. &c. &c.—- 
 
OPERA GLASSES. 165 
 
 Gentlefolks don't like a troublesome thing,— 
 that requires Half a Minute to set it in some 
 particular form, before they can see through 
 it." 
 
 Opera Glasses have been one of my fa- 
 vourite hobbies for the last Thirty Years — 
 and to gain the information contained in these 
 pages, I have carried my experiments to the 
 greatest extent possible, for I think I have 
 tried almost All Apertures and All Focal 
 Lenghs — I had one Object-glass made by 
 Mr. Pierce, of 4 Inches in Diameter — and 
 from that Brobdignagian, he made for me all 
 the intermediate sizes, down to the Lillipu- 
 tian, which I have called my, '^ Invisible Ope- 
 ra G/055," whose Object-glass is only -j^^ths 
 of an inch in Diameter, and of which an ac- 
 count is given in page 93. 
 
 My favourite Single Obj.ct-glass Opera Glass^ 
 which is very portable, and very light, for 
 it only weighs two Ounces, — has a Piano 
 Convex Object-^lass, of one inch and -^oths 
 in Diameter, and usually magnifies 2i, but 
 w^ith a deeper Eye-glass of 1 ^%lhs for Com- 
 mon Eyes, or If^j^ths for the extremely short- 
 sighted, Mr. Doilond informed me, may be 
 made to magnify about 4 times, and is in his 
 Catalogue called the Middle Size Opera 
 Glass, with a Nourse Skin tube, and mounted 
 with dyed Ivory-— its price £l. 1 
 
1§G OPERA GLASSES. 
 
 The most effective Achromatic Opera-glass for 
 general use, which I have seen, is Mr. Dol- 
 lond's Bell Opera of an Inch and a Half aper- 
 ture^ with a Power of 4 — it is conveniently 
 portable, an entertaining companion at a Play- 
 house, and a very pleasant Prospect-glass. 
 
 If the Eye-glass is changed, for One v^^hich 
 makes it magnify Twice, it will be an excel- 
 lent Instrument to assist the Sight to view 
 distant Pictures at Exhibitions, c^c, which it 
 will shew with very beautiful effect — and 
 Short-sighted persons (especially) will find it 
 an incomparable assistant to give them a 
 General View of the Constellations^ — ^and it also 
 deserves to be recommended as an excellent 
 Finder to such as are fond of turning out on 
 a fine frosty night to sweep the sky for a 
 Cornet^ — those who are not, or have not 
 Courage or Constitution to brave the incle- 
 mency of mid^night Frosts and Damps, with* 
 out which, actual Astronomical Observations' 
 cannot be made, I recommend to pay a visit 
 to the 
 
 OURANOLOGIA,* 
 
 * This Lecture on Astronomy and the Phmnomena of the 
 Heavens and of the Earth., is annually given during Lent, 
 at the English Opera House, on a Magnificent Orrery, de- 
 scribing a circle of One Hundred and Thirty Feet, In this 
 Immense Machine^ the jSun, and all the Planets and Sa^ 
 
OPERA GLASSES. 167 
 
 in which is shewn the most beautiful and 
 perfect Orrery ever exhibited, and is one of 
 the most Instructive Exhibitions that youth 
 can be taken to. 
 
 '^ Stars teach as well as shine." 
 
 " An Undevout Astronomer is mad.'' 
 
 ^^ The Heavens are telling the Glory of GoD, and the 
 Firmament sheweth his handy work." 
 
 " These are Thy Glorious Works, 
 Parent of Good, Almighty." 
 
 ^' A Deity believ'd, is Joy begun ; 
 A Deity ador'd, is Joy advanc'd; 
 A Deity belov'd, is Joy matur'd." 
 
 Dr. Young. 
 
 The late Astronomer Royal, Dr. Maske- 
 LYNE, who was short-sighted, had a BinGCular 
 Opera Glass^ i. e. two Opera Glasses, magni- 
 fying about ivvice, fixed in the opening of a 
 Spectacle frame, which he placed before his 
 Eyes, like as you put on Spectacles. I re- 
 member seeing a pair of such Spectacles in 
 
 tellites revolving round him, are seen in motion, with their 
 comparative Diameters and Orbits, The Comet of 1811, 
 descending in its eccentric orbit towards the Sun, arriving 
 at its perihelion, and retrograding, being an original and 
 entirely novel mode of exhibiting and illustrating this beau- 
 tiful Phenomenon. 
 
 Mr. Bartley well deserves the fame he has acquired, 
 by the impressive manner in which he delivers his illustra- 
 tions of these sublime subjects, which are expressed in 
 terms perfectly intelligible, and spoken so distinctly, as to 
 be perfectly audible in the most distant parts of the Theatre, 
 
168 OPERA GLASSES* 
 
 the Observatories, of Mr. Larkins, on Black- 
 heatb Point; of Mr. Aubert, at Highbury 5 
 and of Mr. Hodgson — at Hoddesdon. 
 
 For those purposes which do not require a 
 Magnifying power exceeding 24 — a Single Ob" 
 ject Glass of 54 inches focus, and of ly%ths in 
 diameter, is^ very nearly^ quite as good as an 
 Achromatic^ and costs only half as much. 
 
 The Colorific, and Spherical Aberrations, 
 which cause that fringe of colour, and indis- 
 tinctness around the margin of the field of 
 view of Single Object-glasses — which arise 
 in an extreme degree, when the Aperture of 
 a Single Object-glass, is too large, for its fo- 
 cal length — or the Eye-glass is too short and 
 magnifies too much — and are sometimes so 
 glaring when such a Glass is pointed at a 
 highly illuminated object in the Day time — 
 are often hardly, if at all, perceptible in a 
 Theatre^ unless it be directed to the Lights. 
 But half the errors of aberration arising from 
 the over large apertures of Single Object 
 Glasses are rendered imperceptible in most 
 Opera Glasses — either by a small Stop cut- 
 ting off half of the cone of rays, or the Eye 
 Glass, or aperture in the Eyehead, not being 
 half large enough to receive them — and while 
 the observer imagines that his Object is illu- 
 minated by an aperture of II inches, perhaps 
 
OPERA GLASSES. 169 
 
 he has, in fact, not the use of an aperture 
 of H. 
 
 Concave Eye-glasses may be had for 1.9. 65. 
 each — and it will aftbrcl some amuser eni to 
 have three or four — Magnifying 2 and 3 
 times, for viewing Pictures — 4 for the Theatre 
 — and 5 or 6 as a Perspectivt Glass^ for use at 
 a Review, or on a Race-course, &c. For 
 15s. every degree of Concave may be pur- 
 chased — that is from Two inches to One inch 
 focus — proceeding by tenths of inches : thus 
 — any one who is anxious to give his Eye all 
 the assistance that Art can afford it, may 
 readily do so to the utmost nicety. 
 
 The following Rules will serve for ascertain- 
 ing the comparative decrees of the Magnifying 
 Power of several Eye Glasses^ although, gen- 
 tle Reader, you may think that the 1st — is 
 one of the completest Paradoxes you ever 
 met with. 
 
 1st. " The more a Glass Magnifies^ the more 
 it Diminishes ;" — i. e. if you have two Con- 
 caves^ or Convexes^ and wish to know which 
 magnifies most — hold one in each hand, 
 about one foot from your Eye, and about five 
 feet from a window frame — the Lens through 
 which the panes of Glass appear leasts — mag- 
 nifies most: — this is the readiest way of 
 15 
 
170 OPERA GLASSES* 
 
 ascertaining the comparative power, of various 
 Lenses, 
 
 2d. The further the Eje-glass requires to 
 be removed from the Object-glass, and the 
 more the Inner tube must be drawn out — the 
 more the Eye-glass magnifies. If an Opera 
 Glass magnifies 3, and the Eye-glass is chang- 
 ed for a concave which is a little deeper ta 
 make it magnify 4 times, to obtain distinct 
 vision the tube will require to be drawn out 
 fiirther. 
 
 The Double Object-glass before-mentioned 
 is an Inch and a Half in Diameter; its 
 length, when in use, when it magnifies 4 
 times, is about 4 Inches; and with its tubes 
 weighs 3 and i Ounces ; — a larger Glass is 
 cumbersome to carry, — an unsightly machine 
 to use ; — and the additional Illuminating and 
 Magnifying power gained by a larger aper- 
 ture and longer focus — are in a Theatre, of 
 very little, indeed 1 think of no use. 
 
 There is no need of a Magnifying power 
 of more than 4 times — nor of a pencil of rays 
 of more than three tenths and three quarters 
 in diameter, which is given by an Object-glass 
 of an Inch and a Half in diameter. 
 
 That the Field of View is considerably 
 larger through an Object-glass of Two inches 
 in diameter, if the Magnifying power be as 
 much as 4 times, is a Vulgar Errors 
 
OPERi. GLASSES. 171 
 
 The increase of the field of view in the 
 larger Object-glasses is comparatively very- 
 trifling, and much more than counterbalanced 
 by their unwieldly weight and length. — More- 
 over, the difliculty of making Object-glasses, 
 as their diameter is increased, increases in so 
 high a ratio, that those of Two inches, very 
 rarely define Objects so perfectly and sharply, 
 as those of an Inch and a Half in diameter. 
 
 In every department of Art, the acmi of 
 perfection is always partly accidental, and is 
 not to be attained with undeviating certainty 
 by any Rules; and as there are 100 of li 
 made for 1 of 2 inches aperture — it is in the 
 like proportion, more easy to select a Fine 
 One. 
 
 Imperfections in the Object-glasses of Opera 
 Glasses, like those of Telescopes, are magni- 
 fied and become evident, as the Magnifying 
 power of the Eye-glass is increased. 
 
 Defects in an Object-glass which, when it 
 magnifies only Twice, are almost impercepti- 
 ble — when it Magnifies Four or Five times, 
 become too glaring to pass muster before a 
 good Eye — the Vision, (especially the mar- 
 gin of the field of view.) becoming less Sharp, 
 and the edges of the Objects being fringed 
 with Colour. 
 
 Opticians charge £2. 12^. 6d. for the Best 
 
172 OPERA GLASSES^ 
 
 Achromatic Opera, in a plain mounting, with 
 an Object-glass of 14 inch in diameter and 
 which magnifies 4 times — £2. 2s. for the 
 Common Achromatics, which magnify 24 — 
 and £\. \s. for those of like power with Sin- 
 gle Object-glasses. 
 
 I must here caution my Reader, that the 
 real, or the relative powers, of various Opera 
 Glasses, can only be accurately appreciated by 
 actual trial in the Theatre^ m which they are 
 to be used — especially, comparisons of Ach- 
 romatic and Single Object-glasses ; and unless 
 particular care be taken that they are glass- 
 ed with precisely the same kind of Glass—- 
 w^ith Concaves which give precisely the same 
 Magnifying power — and the Glasses are di- 
 rected to the same Object, at, as nearly as 
 can be, the same time ; and the Ocular Glass- 
 es and Object-glasses are all perfectly clean 
 — Comparison will be in vain. 
 
 The difference of even 34 and 4 in the 
 degree of Magnifying, will, with some objects, 
 give quite a different character to an Opera 
 Glass,— -even if the Object-glasses and Eye- 
 glasses are equally good. 
 
 An ifiCxperienced person, will say that 
 the Opera Glass which magnifies 4 times, 
 defines some objects more distinctly than that 
 which magnifies only 34— but that there is a 
 
OPERA GLASSES. 173 
 
 greater degree of brightness about the latter, 
 and that the vision in it appears clearer : — 
 This, is thus to be accounted for,—- //le lower 
 the Power^ the clearer and brighter objects 
 appear — and upto a certain maximum, (which 
 I think for use in a Theatre is about 4 fimes,) 
 the higher the Power the better minute objects 
 will be defined, and the sharper and more 
 distinct the Vision will appear. 
 
 The Achromatic Object-glass above-men- 
 tioned, is composed of a Piano Concave lens, 
 and a double Convex^^ which, combined, are 
 generally (in every part) of the thickness of 
 about |ths of an Inch. 
 
 The thickness of the usual Piano Convex 
 Single Object-glass of the like focus, — in the 
 central and thickest part of it is seldom more 
 than fths of an Inch, and in the thinner parts, 
 not half that : — however, such is the advan- 
 tage of the Achromatic — that if you compare 
 m Single^ and a Double Object-glass of li 
 
 * Sometimes a Film or Fog forms between the Object- 
 glasseSy or, as the Optical phrase is, *' the Glasses sweat :" 
 — when this happens, they must be taken out of their cell 
 and wiped with a bit of soft Leather or of very fine Silver 
 Paper— but never do this but when it is absolutely needful 
 •—and then, take care to replace them in the same position ; 
 it is seldom requisite oftener than once or twice in a Year. 
 Nor wipe the Object or Eye-glass except they really require 
 it — as often as you wipe them— you scratch them a little. 
 15* 
 
174 OPEtlA GLASSES. 
 
 inches in Diameter and 4i inches focus, and 
 put to them Eye-glasses which make them 
 magnify 4 times, you will find that Vision, 
 (excepting just in the centre of the field of 
 view in the Single Object-glass,) is more 
 distinct, and objects are more sharply defined 
 through the Double, than they are with the 
 Single Object-glass. If you contract the 
 aperture of the Single Object-glass to 1-^, 
 you will find the Errors of Aberration consi- 
 derably duninished — and more so if you li- 
 mit it to l^yhs, and if the focal length of your 
 Single Object-glass is increased from 4i to 
 6 Inches, its vision will be still more im- 
 proved. If its aperture be 1 v\ths, the open- 
 ing of the Stop must be limited to a little less 
 than 3%ths of an inch in diameter. 
 
 Tenths the Object-glass 
 is in Diameter. 
 
 Mag. Power 4)12 (y^hs, Diameter of the 
 12 Pencil. 
 
 The Chromatic and the Spherical aberra- 
 tions which produce prismatic colours, and 
 distort the Vision in the Margin of the field 
 of view, — exceeding^ly distress the Eye, and 
 which are the main Evil of Single Object-glasses 
 which have a larger aperture in proportion 
 to their focal length than an aperture of l^ths 
 
OPERA GLASSES. 
 
 inches, to 5i — and which magnify more than 
 3 times, are in a great measure corrected in 
 Double Object-glasses, vvilh vvhic h the Image 
 of Objects appears more Distinct, in propor- 
 tion as the order in which the Rays proceed 
 is better preserved. ^ 
 
 The Grand superiority of the Double or as it 
 is commonly called Achromatic Object-glass^ 
 consists in the field of view being almost 
 quite as distinct at the margin, as it is in the 
 centre, and thus. Vision is made easy lo the 
 Eye, w^ith a considerable Magnifying power. 
 
 The Eye, is sadly puzzled, how, to adjust 
 itself with a Single Object-glass, when it 
 magnifies more than 3 times — (especially if 
 its focus is less than 54 inches and its diame- 
 ter more than H), which then becomes indis- 
 tinct, except just in the very centre of the 
 Field. I think that in the very Centre of the 
 field of a Single Object-glass, the vision is 
 quite as vivid, if not more so, than it is in a 
 Double Object-glass — but as only just the 
 very middle of the field is distinct—looking 
 through it, soon becomes much more fatiguing 
 to the Eye than with a Double Object-glass. 
 
 Those who wish to prove this, may get a 
 Single Piano-Convex Object-glass for five 
 shillings, of exactly the same diameter and 
 focus as the Achromatic one I have recom- 
 
176 OPERA GLASSES. 
 
 mended in page 157, — and judge for them- 
 selves. If Vision is distinct, when the Sin- 
 gle Object-giass is at the sanrie distance from 
 the same Eye-glass, as when the Double one 
 is used, the Magnifying power will be the 
 same — if the Eye and Object-glass must be 
 brought nearer together—the Magnifying 
 power is less, and the Single Object-glass is 
 of too short a focus — to have a fair compari- 
 SQ7i^-— the focal length of each Object-glass^ must 
 he exactly the same* 
 
 For a Single Object-glass, to be at the Sc.me 
 distance from the Eye-glass as a Double One 
 of the same focus, the Eye-glass must be 
 brought, apparently, full ^-^ih^ of an Inch 
 nearer to the Single Object-glass— to make 
 up for the Double Object-glass projecting so 
 much further up the Tube than the Single 
 One does. 
 
 I formerly thought, that for use in a Thea- 
 tre, the Single Object-glass was best. 
 
 Until Mr. Pierce, about Five Years ago, 
 just before he retired from business, made me 
 an Acbrcojatic Opera glass, which magnified 
 4 times, 1 had not seen a Double Object 
 Glass, nor do I think one had been made, 
 which magnified more than 2J, which is the 
 power usually put to those commonly sold. — 
 My own excellent Single Object-glass, which 
 
OPERA GLASSES, 177 
 
 Mr. p. made for me, magnified rather more 
 than 34 -— it is no wonder then, that I prefer- 
 red it to the ineffective Double ones vvhi^h 
 only magnified 2i. 
 
 The reasons why Opera-glasses were for- 
 merly not made to magnify more than 2i~ 
 were, that the small size of the Theatres at 
 the time these instruments were originally in- 
 vented, did not require more magnifying pow- 
 er, — and that with such a low power, the im- 
 perfections in vision arising from the Spheri- 
 cal and Colorific aberration of the Single 
 Object-glasses of the very large"^ Apertures, 
 v^ith which it has been the fashion to make 
 them latterly, were comparatively trifling— 
 indeed, an Opera-glass seems hitherto, to 
 have been considered ^s^apreUy Thing to Look 
 at — or a Play Thing to Look through- — 
 rather, than — an useful and entertain- 
 ing Instrument to See with, — its Proper 
 Powers have never before been explained — 
 with such Low powers, they were easy to 
 Opticians to make, and to their Customers 
 to use. 
 
 I feel no awkwardness in publishing: this re- 
 cantation of my former Opinion respecting 
 Single Object Glasses — but willingly em- 
 
 * The origin of these Great Single Object Glasses of so 
 short a focus, was an attempt at an imitation of the aeter' 
 nal appearance of the Achromatic Opera Glass, 
 
178 OPERA GLASSES* 
 
 brace this welcome opportunity of acknow- 
 ledging my Error— to want the Candour to 
 do so, — would be to want the Courage to con- 
 fess that I am wiser To d iy, than I was Yes- 
 terdays—remembering the excellent Advice 
 given bj Pope in the 368th and following lines 
 of his Essay on Criticism. 
 
 • '^ Positive, persisting Fops ws know, 
 
 WhOj if once wrong, will needs be always so; 
 But You, with pleasure own your Errors past, 
 And make each da}^, a Critique on the last." 
 
 To measure the Magnifying Powers of Opera 
 Glasses * 
 
 Look at one object at the same time with 
 both Eyes, — one eye viewing the object 
 through the Glass — and the other without it. 
 
 You will find som^ difficulty at first in keep- 
 ing both Eyes open in this unusual way, while 
 looking through the Glass ; but after a few 
 trials you will be surprised at the great accu- 
 racy and ease with which the Powers can be 
 ascertained. 
 
 The Object to be viewed, must not be more 
 distant than what the naked eye can distinctly 
 define : and not less distant than 60 or 80 feet. 
 For this purpose, the best Object to be viewed, 
 is perhaps the front of a huilding of regular 
 stone work, with indented horizontal joints: 
 or when such an object does not readily oc« 
 
OPERA GLASSES. 179 
 
 cur, a building of good regular brickwork will 
 in general be found to answer tolerably well : 
 other objects, as the squares of glass in a long 
 window, which are usually of the same size, 
 will be found convenient for the small powers 
 that are usually applied to Opera-glasses. 
 
 It will be obvious, from what has been said, 
 that the object to be vievred must consist of 
 a number of equal divisions in the height. 
 These divisions must be regarded by one eye 
 through the Opera-glass at the side and close 
 against the object as seen by the other eye ; 
 and the number of divisions seen by the nak- 
 ed eye in the height of one division as seen 
 through the Glass, is of course the Magnify- 
 ing Power. 
 
 The foregoing process gives the Magnify 
 ing power in wliole numbers. It is, however, 
 desirable sometimes to ascertain the power 
 of an Opera-glass to the fraction of one 
 quarter : this may be done by marking every 
 fourth course of brick-work with a chalk line ; 
 and the number of these chalked divisions 
 and the additional joints of brick-work seen 
 wdth the naked eye, in the space of one 
 chalked division as seen through the Teles- 
 cope, gives the Magnifying power in whole 
 numbers and quarters. 
 
 The Magnifying Power of any Object Glass 
 
1 80 OPERA GLASSES, 
 
 of an Opera Glass, is in proportion to its dis- 
 tance from the Eye Glass— as I have before 
 observed. Therefore — a person who is so 
 Short-Sighted as to use a Concave No. 4, does 
 not derive that degree of advantage from an 
 Opera Glass, that a Common Eye does— the 
 same Opera Glass which only magnifies 3i 
 for him, — v/ill magnify 4 for a Common Eye^ 
 and for a Long Sighted Eye of 60 Years old, 
 which requires convex Spectacles to read 
 with, of 18 Inches focus, it may magnify 4i 
 or perhaps rather more. 
 
 Shorty and Long Sighted Eyes when they 
 look through an Opera Glass, with their Spec- 
 tacles on — will see at the same focus, and con- 
 sequently with the same Magnifying Power 
 as Common Eyes — and without Spectacles the 
 JN'ear Sighted will have about, or almost, half 
 a degree less^ — ihe Long Sighted^ about as 
 much more Magnifying Power. The exact 
 Focal length of the Eye-glass which is best 
 for any peculiar Eye, will be best determined 
 by Experiment. See page 154. 
 
 Lastly — take care that the front edge of 
 the cell containing the Ohject-glass projects at 
 least the 10th of an inch beyond the surface 
 of the middle part of the Glass — that it may 
 be properly defended when laid down ; and 
 that it may not be soiled by the stuffing in 
 the top of the case coming against it ; this said 
 
OPERA GLASSES. 181 
 
 Stuffing is a mighty silly decoration, and 
 much better omitted- — if the inside of the top 
 of the case be required to be double natty — 
 let it be lined with bright green Velvet,-— 
 The Eye-end should be sufficiently distant 
 from the Eyeglass to prevent any thing touch- 
 ing it. 
 
 Diagonal Opera-Glasses.-- To the object 
 end of an Opera-glass may be attached a 
 plane mirror, placed at an angle of 45 de- 
 grees, like the small speculum in a Newtoni- 
 an Telescope : if this be well made, and the 
 lateral aperture is as large as the Object- 
 glass, the Illuminating power is so sufficient, 
 that the light lost by the reflection is almost 
 imperceptible, and the Diagonal is almost 
 quite as bright as the Direct vision. 
 
 This is an entertaining Optical Plaj^thing, 
 with which, you may observe distant objects, 
 as unobservedly, as you can those which are 
 near with the QVci^m^pec^or, mentioned in page 
 75 of this work— as the Instrument points to 
 a different object from that which is viewed 
 - — and as there is an aperture on the side, it 
 is almost impossible to guess which way you 
 are observing. 
 
 However trifling in value, or however inv 
 16 
 
182 OPERA GLASSES* 
 
 perfectly expressed the foregoing Observa- 
 tions I fear are in many respects, notwith- 
 standing the extreme labour and care I have 
 bestowed in order to be accurate and intelli- 
 gible — 1 hope, that my Reader will give me 
 credit for having done my best, to put him 
 into complete possession of all the '^ Practi- 
 cal Facts" which I have been able to accu- 
 mulate. 
 
 Of the many " Casdes in the Air," which 
 Theory has built at the expense of Truth, — 
 there are none more numerous, or less sub- 
 stantial, than those which have been set 
 up by Speculative Op icians. — I have not 
 aimed at amusing the Imaginations of such 
 Ingenious Persons with abstruse Algebraic 
 calculations, — or of amazing the reader with a 
 confounding crowd of cramp Technical terms 
 which are only intelligible to Practical Opti- 
 cians — by which, if some Writers have suc- 
 ceeded in exciting 
 
 " Wits and Philosophers, Scholars and Conjurers," 
 
 to admire their amazing erudition — it has 
 been at the unwise expense, of rendering their 
 works entirely useless to the Public. 
 
 The humble efforts of the Author, have 
 been confined, to an ingenious Endeavour to 
 give a plain unvarnished account of the actu- 
 al results of his experience, in so clear a 
 manner that — All may easily and exactly 
 Understand, 
 
OPERA GLASSES. 183 
 
 Truths interesting to All, should be told in 
 Terms intelligible to Alh 
 
 Errors, and Omissions, will no doubt be 
 found, and from enlightened Readers,— will 
 meet indulgence — They, — know,-— how un- 
 avoidably, — and how often, — such defects, 
 will escape the most persevering industry, 
 and most unremitted attention. 
 
 Those who are already well acquainted 
 with the subject, which I have devoted many 
 an hour to illuminate so plainly, that I hope 
 All may understand, may think I have upon 
 some matters, been tediously minute, — but if 
 I had not written so fully and so plainly — I 
 could not have enjoyed the main gratification 
 I receive from publishing this little book — 
 the pleasure, of hoping, that it will give an 
 attentive Reader, in a Few Hours — ^what 
 the Writer, has been collecting Many Years. 
 
 ^' Content, if hence th' unlearn 'd their wants may view. 
 The learn'd reflect on what before they knew : 
 Careless of censure, nor too fond of fame ; 
 Still pleas'd to praise, yet not afraid to blame ; 
 Averse alike to flatter, or offend ; 
 Not free from faults, nor yet too vain to mend." 
 
 Pope. 
 
 CHAPTER XIX. 
 
 THEATRES. 
 
 I AM informed that the distance from the 
 
184 THEATRES. 
 
 front of the opposite Boxes to the ( 'urtaio 
 
 is — 
 
 At the English Opera House 50 Feet. 
 
 Drury Lane - » - 60 — 6 Inches 
 Covent Garden - - 63 — — 
 
 I am I believe correctly informed, that at 
 the Theatre which Garrick rebuilt in Drury 
 Lane^ and where he estabSisher! his immortal 
 fame, the distance from the Front Boxes to the 
 Curtain was not more than 47 feet 6 inches^'— 
 and am disposed to attribute no small part of 
 the great admiration which I hear that he 
 excited in those who saw him act, and who 
 speak still of the extraordinary distinctness 
 with which he spoke, and of the variable and 
 incomparable expression of his Countenance, 
 — to the Spectators being so much nearer to 
 the Stage. 
 
 I understand from the best authority, that 
 at the cotemporary Theatre of Covent Gar- 
 den^^ the distance of the Spectators from the 
 Performers was then 8 feet further, i. c. b^ 
 feet — and that the disadvantage of this great- 
 er distance, was then frequently remarked 
 and complained of. 
 
 " In most theatres, whoever wishes to have 
 a tolerable view of the Stage, must be situat- 
 
 *"In this Theatre, 1 foot 9 inches was the whole space 
 allowed for seat^ &c, though a moderate-sized ^jerson can- 
 
•theatres. 185 
 
 ed beyond the reach of the Actor's voice — 
 but if he wishes to be near the St^ge, he is 
 (in the Boxes) miserably seated sideways — 
 I am confident, that where the distance of 70 
 feet from the Scene to the opposite Boxes is 
 exceeded, the Actor will be heard very im- 
 perfectly. 
 
 " It is an universal custom to take the point 
 of Sight for the Scene Painting-^-dii the centre 
 of the front of the opposite boxes ; and this, 
 not only for the flats or end scene, but for 
 the side scenes also, in which it is necessary, 
 in many instances, to represent one continued 
 line, such as the side of a Room, &c. ; in which 
 case, the least remove from the centre breaks 
 this line and weakens the efl'ect of the scene. 
 This demonstrates that our painted Scenes 
 can be viewed to a proper advantage in one 
 situation only ; and that they will appear de- 
 fective in proportion as they are viewed at a 
 distance from this point. 
 
 " It has often been observed, that if we view 
 a person at a greater height than an Ancrle 
 of 45 degrees, the features appear distorted 
 and the expressions grimace. 
 
 not conveniently sit in less space than that of 1 foot 10 
 inches from back to front, nor comfortably in less than 
 2 feet."— G. Saunders, Treatise on Theatres, 4to, 1790, 
 p. 84. 
 
 16 * 
 
186 THEATRES. 
 
 " To discern well the motions of the fea- 
 tures, we cannot be too near the Actor c il is 
 with great difficulty we comprehend the . at 
 the distance of 75 feet, and scarcely with a- 
 tisfaction at more than one-third of that dis- 
 tance. 
 
 *^ Having traced a Circle of 100 feet ia 
 diameter, 1 placed the speaker in the centre ; 
 the distance, therefore, was the radius of 50 
 feet every way— the hearer moving in the 
 circumference of this circle, heard most dis- 
 tinctly when in front of the speaker, not much 
 less so on each side, but scarce at all behind, 
 and contrary to the common notion, that 
 Sound ascends further than it descends— 
 that 
 
 " The Descension of sounds exceeds the 
 Ascension. '' 
 
 Exp, 2.—" The Well-hole of the Staircase 
 in St. Paul's Cathedral, which is free of any 
 redundancy of sound, is about 8 feet in diam- 
 eter, encircled by^a stone wall, and covered 
 with a skylight. At some distance from the 
 bottom, and near the top, were alternately 
 placed Speaker and Hearer ; when the Voice 
 descending was heard at the distance of 80 
 feet, ascending 70 feet.'' — From the interest- 
 
THEATRES. 187 
 
 ing Treatise on Treatres^ 4to, 1790 (published 
 by Tnylor at the Architectural Library' in 
 Hoi born), pages 91,2, 4 and 6: this entertain- 
 ing Volume gives a Description, and the Plans 
 and Dimensions, of all the principal Theatres 
 in Europe; and in which those who desire 
 further information on such subjects, will find 
 it both minutely and plainly set forth. 
 
 I attribute Mr. Garrick's superlative suc- 
 cess, to his proximity to his Audience. I can- 
 not imagine, that there is any Part which the 
 English Roscius of that day played, — but that 
 several of our present excellent Actors per- 
 form quite as v/ell. 
 
 If our Actors appear to fail in any part, it 
 arises from no other cause than occasionally 
 being obliged to overstrain their Voice, 
 (which cannot be done without some distor- 
 tion of the features,) from being at Drury 
 Lane 13, — and at Covent Garden 15 feet 6 
 inches, further from the Audience than in 
 Mr. Garrick's Theatre — the very superior 
 illumination given by the Argand lamp foot 
 lights, side lights, &c. and the Brilliant'Gas 
 light Chandeliers which are suspended from 
 the centre of the Ceiling, in a great measure 
 counteract the disadvantage of the increased 
 distance, as far as the Eye is concerned, espe- 
 cially when it is assisted by a good Opera 
 Glass. 
 
108 THEATRES, 
 
 The Magic power, which some Performers 
 seem to possess, of making themselves heard 
 distinctly n\\ over the House, without any 
 apparent effort — depends infinitely more on 
 the faculty they have of catching and caging 
 the intense attention of the whole Audience 
 — than upon any extraordinary exertion of 
 their Voice. 
 
 In Mr. Arnold's Theatre, the distance 
 between the Performer and the Spectator is 
 only 2 feet more than it was in Mr. Gar- 
 rick's House. 
 
 The following accurate account of the 
 Building of the present Drury Lane Thea- 
 tre will, I think, be as interesting to the 
 Reader as it is honourable to the Judgment 
 and the Integrity of Mr, Benjamin Wyatt, 
 the Architect who built it. 
 
 The Amount of the Original Estimate for 
 the present Drury Lane Theatre, as design- 
 ed by Mr. Benjamin Wyatt, was JGII8.85O5 
 calculating on the work being completed on 
 the ^\st of December, 1812. 
 
 It being subsequently decided, that the 
 Portico and the external Composition upon 
 every front, excepting the West front, should 
 be omitted, the Estimate was reduced to the 
 sum of £1 1 2,750 ; those Items having stood in 
 the original Estimate at the sum of jEejlOO, 
 
THEATRES. 189 
 
 After the Estimate had 
 thus been reduced to the 
 sum of £112,750, certain 
 extra works were decided 
 upon, which {previously to 
 such decision) were com- 
 puted at £11,540 
 
 During the progress of 
 the work it was decided 
 that the Theatre should 
 be opened to the Public 
 on the lOth of October^ 
 instead of on the 31^^ of 
 December^ 1812, as at first 
 intended ; the addition- 
 al expense arising from 
 which alteration was cal- 
 culated at the sum of - jei,500 
 
 Making, together with 
 the foregoing sum, a total 
 of ----- - -£13,040 above the 
 
 reduced Estimate. 
 
 Which sum of £13,040 
 added to £112,750, (the 
 amount of the reduced Es- 
 timate) makes a total of - - - £125,790 
 which was the precise sum actually paid for 
 the Building; so that in fact the Proprietors 
 never were subjected to One Shilling of expense 
 
190 
 
 THEATRES. 
 
 for the Building beyond the amount at which it 
 was estimated; although, from the alterations 
 above stated, h\ the work executed, the Esti- 
 mate was, from time to time, either diminish- 
 ed or augmented. 
 
 The Building: was commenced on the 21st 
 of October, 1811. and opened to the Public 
 on the lOih of October, 1812, a period of 
 little more than eleven months. 
 
 Distance from 
 
 the Curtain to the 
 
 Front Bnxep. 
 
 Number of Pv.r- 
 
 sons the Seats in 
 
 the Boxes will 
 
 contain. 
 
 Oj o 
 
 6 
 
 3 
 
 At the Feet. 
 English Opera House, ^^ 
 in 1823. ^" 
 
 700 
 at 5s, 
 175/. 
 
 650 
 at 35. 
 97/. 10 
 
 400 
 
 at 25. 
 40/. 
 
 Drury Lane, ^^ « 
 in 1823. ^^--^ 
 
 1134 
 396/. 18 
 
 700 
 122/. 16 
 
 500 
 50/. 
 
 Covent Garden, ^^ 
 in 1«21. ^'^ 
 
 1000 
 
 at Is. 
 350/. 
 
 700 
 at 35. 6d, 
 122/. 10 
 
 500 
 
 at 25. 
 
 50/. 
 
 Hay market, 
 in 1823. 
 
 
 750 
 
 at 5s, 
 
 187/. 10 
 
 400 
 
 at 35. 
 
 60/. 
 
 320 
 
 at 25. 
 32/, 
 
THEATRES # 
 
 1^1 
 
 For the foregoing Calculations T am in- 
 debted to Mr. Arnold, Mr. Winston, and Mr. 
 James Brandon. 
 
 '*• When His Majesty went to Covent Gar- 
 den Theatre on February 7rh. 1 821, ihe Per- 
 formances were 'JwelfthJ^ight \ul Harlequin 
 and Friar Bacon — Iweive Hundred People 
 paid to the Boxes — hut iture is not Siding 
 room for more than a 1 houband." — Mr. J. 
 
 6 
 
 JO 
 
 B to 
 
 1° 
 
 >> 
 
 V 
 
 s 
 o 
 
 o 
 o 
 
 o 
 
 > 
 
 250 
 
 at Is. 2000 
 12/. 10 
 
 325/. 
 
 In the Private 
 
 Boxes, 
 
 160 Persons. 
 
 300 
 15/. 
 
 2634 
 
 584/. 14 
 
 16 Family Boxes, 
 124 Persons, 
 
 24 Piivute Boxes, 
 192 Persons. 
 
 300 j 
 
 at Is. 1 2500 
 15/. 1 
 
 537/. 
 
 26 Private Boxes, 
 172 Persons. 
 
 200 
 
 at \s. 
 
 10/. 
 
 1670 
 
 289/. 10 
 
 14 Private Boxes, 
 98 Persons. 
 
192 ^ THEATRES. 
 
 Brandon^ late Box Book-keeper to Covmt 
 Garden Theatre, 
 
 When His Majesty visited Drury Lane 
 Theatre on Monday, the 1st of December, 
 1823, every part of it was crowded to ex- 
 cess — but I could not learn the exact num- 
 ber of the Spectators. 
 
 When The King went to Covent Garden 
 Theatre^ on Wednesday the 3d of December, 
 1823, the Performances were The Cabinet 
 and Tirnour the Tartar^ and the number of 
 Persons who paid to the 
 
 Boxes ...... 1936 
 
 Pit ------ - 1123 
 
 Gallery ..... 776 
 
 Upper Gallery - - - 420 
 
 4255 
 exclusive of Private Boxes. 
 
 The above account was given to me by 
 Mr. Robertson^ the Treasurer to Covent Gar- 
 den Theatre. 
 
 It appears by this Document, that such 
 was the universal and earnest desire of His 
 Majesty's Loyal Subjects to behold their 
 Gracious Sovereign — that a greater number 
 of Persons assembled in the Theatre on that 
 Evening, than had ever been within it on 
 
god! save the king. 193 
 
 any previous performance : the whole scene 
 was most brilliant. 
 
 " God ! save the King" 
 
 was sung several times. Many appear to 
 have taken much pains to shew — When our 
 favourite National Anthem was composed^ — I 
 have endeavoured to shew — how it ought to 
 be Sung* with 
 
 *^ Good Emphasis and Good Discretion." 
 
 See No. 4. of " the Loyal and National Songs 
 of England." 
 
 Perhaps the latter information, may be as 
 useful as the former — for I remember to have 
 read in " The Cook^s Oracle^'^^ that — '^it is no 
 
 * Never having seen a Complete Score of "God s.ave 
 THE King" for a full Band, Vocal and Instrumental, — I 
 have given one, and have marked the words as they ought 
 to be expressed, in " The Grand Selection of the Loyal, 
 National, and Sea Songs of England, published in 
 Commemoration of the Coronation of King Gf.orge the 
 FoTTRTH, and most humbly Inscribed, and with Gs anions 
 Permission dedicated to the King^s most ExcellE-\t 
 Majesty by William Kuchiner, M.D. 
 
 Printed for Hurst, B obiason, and Co. Booksellers to 
 His Majesty, No. 90, Cheapside, and No. 8, Pall- 
 mall, in which is now fiist printed, from the Original 
 MS. in the possession of tlie Editor, Dr. John Bull's 
 "®fO?l m\St tlir lilllge''— A.D. leie, and a Fac- 
 simile of the earliest printed Copy of *' God save the King^' 
 (1745) and 110 other Loyal, National, and Sea Songs 
 of England. 
 
 17 
 
194 god! save the king* 
 
 matter how Good your Meat is, — if it is not 
 well Dressed." 
 
 1 believe, 1 am entitled to the honour of 
 having given the first hints which have been 
 written, as to Hozi' what is Sung so often ought 
 always to be Sung. 
 
 " The Words being marked with proper Em- 
 phasis—it is presumed will infinitely heighten 
 the effect, and may be a standard for the 
 performance of it — and ensure^ the proper 
 pronunciation of the Words^ and the effective 
 expression of the Music ; and revive that har- 
 monious combination of them, the want of 
 which has long been deplored, — by all who 
 have faculties to comprehend how great is 
 their power when united, and 
 
 " Sound is married to immortal Verse •"--MiLTOK', 
 
 ^' As soon as this is generally considered, 
 Singers will see their readiest road to fame, 
 is to avail themselves of the double power of 
 making the words an appeal to the Hearts 
 and Understandings of their Auditors — as 
 well as attacking their Ears with Volutas 
 and Cadences, &c. 
 
 "To produce effect on others — Actors 
 must themselves feel the passion they wish 
 to inspire their audience with — and to sing 
 with proper and effective expression, must 
 
god! save the king. 195 
 
 give to every Syllable, and to every Quaver, 
 its exact relative value ; but not Shout and 
 Bawl upon From — To — Of — In — And — But 
 — On^ &c. &c. merely, because they hap- 
 pen to be placed (improperly) under the 
 accented part of the Bar, or under a long 
 note, — or a favourite note in their voice. 
 
 '^ Melody is the soul of Music — Poe- 
 try is the soul of Melody — the warbling of 
 Sounds without the distinct articulation of 
 words pronounced with proper accent and 
 emphasis does not deserve to be called Sing- 
 ing : — it is merely playing upon the voice — 
 a Concerto on the Lari^nx^ and comparatively, 
 as uninteresting as a Frrime is without a Pic- 
 ture. Briefly — The Art of Singing effect- 
 ively — ih to Sing every zvord wit'', the same 
 Accent and Emphasis as You would Speak it.* 
 
 * " The Pupils of our excellent English Composer Dr. 
 ARJfE, were remarkable for their proper pronunciation. — 
 It will be thouirht almost inciedihlc when I relate that all 
 the fine and clear pronunciation of the words which dis- 
 tinguished the late vlr. Kennedy, nat^jral as it appeared, 
 was the entire effect of hard up-hiil application of the Doc- 
 tor's lofiy conceptions of what wus calculnted to touch the 
 Hearts and Understanding of the Auditors. This immense 
 difficulty was often accompanied by tears and sobbings, as 
 impossibilities; but Arjve knew otherwise, and ' Omne 
 tulit pnnctum.' I say it is inconceivable what lights the 
 Doctor threw on the accentuation of each Word, nay on 
 gyery Letter of every v/ord, whether commencing or finishing 
 
196 god! save the king* 
 
 In singing " God ! save the King,^' if every 
 Syllable be sung, as it commonly is, 
 
 " God save great Geoige our King," 
 
 these words are pronounced as if they were 
 spelt — 
 
 Gavv-od say-eev grey-eat Jaw-orge ow-er Kee-ing ; 
 
 thus making Monosyllables into Dissyllables* 
 '' U the proper pronunciation be preserved, 
 it must be thus — 
 
 God ! save great George our Kin^g ; 
 
 the only syllables in this line which should 
 be sung, the time indicated by the notes, are— - 
 
 God ! save — and — George. 
 
 " This Solemn Invocation to the Almighty ! 
 as commonly sung, sounds more like a Song 
 of Triumph, — than a Prayer for the preser- 
 vation of our Sovereign — hardly a word of 
 it, except the first and last line, is heard dis- 
 tinctly. 
 
 " How much would the effect of this Loyal 
 Anthem be increased, if the name of God! 
 
 with either vowels or consonants, so as to render the sense 
 of the SoDg intelligible to the most rommon ears as well as 
 to the most refined. He would pass whole mornings, and 
 never give up the Idea, that the Poetry of a Song ill ex- 
 pressed was a Nullity to the Ui>rievstanding, instead of a 
 Blaze of Light; and thus he succeeded with the British 
 Public." — (Literary Gazette,) 
 
god! SAVE THE KINC. 197 
 
 was uttered with due reverence ! ! ! And if 
 
 Singers would consider, that ''God save the 
 
 King,^'is not a florid Song, — but an Anthem, — 
 
 and like other Anthems admits of hardly any 
 
 ornament beyond an Apogiatura — 
 
 " Sing ye Praises with Understanding,^'' 
 
 Psalm xlvii. ver. 7. 
 
 Instead of vying with each other, which shall 
 introduce most Trills — Shakes, &c. let us try 
 who can most distinctly articulate every 
 Syllable— and most effectively utter every 
 Word! 
 
 " The Loyal Anthem^ is not a singular ex- 
 ample of the want of the coincidence of the 
 Musical, and the Prosodical Accent. 
 
 " It is almost impossible to point out a 
 Song, that can be sung, exactly, as it is set 
 down, from this want of the coincidence of 
 the Rhythms of the Poetry and the Music, — 
 which it is no easy task, even to Singers of 
 superior ability, to adjust perfectly — so as to 
 give full effect to the Poetry; and, at the same 
 time, preserve the Melody," — See Observa- 
 tions on Vocal Music and Singing,"^ 
 
 The following is a Specimen of the manner 
 of marking the Words which it is recommend- 
 ed to Composers to avail themselves of, as a 
 
 * Printed for Hurst and Robinson, No. 90, Cheapside, 
 12mo. 1821, price 4s. 
 17 * 
 
198 god! save the king. 
 
 means of avoiding false Accent and Empha- 
 sis of the Poetry they are sfoing to set — and 
 to Singers, to mark the Words of Songs (as 
 they would spe-ak tiiem) before they think about 
 the Tune, which will enable ihem to correct 
 any little errors of accent, which may have 
 inadvertently occurred in Songs already set 
 to music. This may almost always be ac- 
 complished without any detriment to the Me- 
 lody, and to the infinite improvement of most 
 Songs. 
 
 God ! save Great George, our King, 
 Long live our Noble King, 
 
 God ! save the King ; 
 Send Him victorious, 
 Happy, and glorious, 
 Long to reign over us. 
 God ! save the King, 
 
 2. 
 O Lord, our God ! arise, 
 Scatter his enemies, 
 
 And make them fall ; 
 Confound their politics, 
 Frustrate their knavish tricks, 
 On Thee, our hopes are fix'd, 
 
 save us all. 
 
god! save the king. 199 
 
 3. 
 Thy choicest gifts in store, 
 On George be pleas'd to pour, 
 
 Long may He reign ; 
 May He defend our Laws, 
 And ever give us cause, 
 To sing with Heart and voice, 
 
 God ! save the King. 
 
APPENDIX : 
 
 RESPECTING SPECTACLES. 
 No. I. 
 
 RULES FOR CHOOSING SPECTACLES. 
 BY G. ADAMS, OPTICIAN. 
 
 "When the eye sensibly flattens, all delay 
 is dangerous ; and the longer those who feel 
 the want of assistance, defer the use of Spec- 
 tacles, the more they will increase the failure 
 of the eye : there are too many who pro- 
 crastinate the use of them, till at last they 
 are obliged to use glasses of 10 or 12 inches 
 focus, instead of those of 36 or 40, which 
 would otherwise have suited them ; thus pre- 
 ferring a real evil, to avoid one that is ima- 
 ginary. Mr. Thomin mentions several de- 
 plorable cases of this kind, pririicularly one 
 of a lady, who, through false shame, had ab- 
 stained from wearing Spectacles so long a 
 time, that at last it was impossible to suit 
 her, but with those adapted to eyes that have 
 
'202 APPENDIX. 
 
 been couched. Whereas the instances are 
 numerous of those who, by using glasses of 
 a long focus at the first approach of Short- 
 sightedness, have broug;ht back their eyes to 
 their natural sight, quo been able to lay aside 
 their spectacles for years. 
 
 These considerations point out clearly the 
 advantages that may be obtained by a pro- 
 per choice of spectacles on first wearing 
 them, and the importance of making such a 
 choice ; as the eye will endeavour to con- 
 form itself to any improper focus, and thus 
 be brought into a state of extreme age, at a 
 much earlier period than would have hap- 
 pened had they bee?) suited with judgment. 
 There are very few Opticians but what must 
 have seen instances of those, who by habitu- 
 ating their eyes to too short a focus, or too 
 great a m,a2;nifying power, have so injured 
 those tender organs, as to deprive them of 
 future assistance from glasses. This fre- 
 quently happens to those who purchase their 
 spectacles of hawkers and ]:«edlRrs, men equal- 
 ly ignorant of the science of optics and the 
 fabric of the eye. 
 
 '^ Let it, therefore, be carefully remember- 
 ed, that magnifying power is not the point 
 that is most to be considered in the choice 
 of Spectacles ; but their conformity to our 
 
APPENDIX. 203 
 
 si^ht, their enabling us to see distinctly, and 
 with ease, at the distance we were accus- 
 tomed to read or work, before the use of 
 Spectacles became necessary : or, in other 
 words, glasses should so alter the disposition 
 of the rays, at their entrnnce into the eyes^ 
 as will be most suitable to procure distinct 
 vision at a proper distance; an end of the 
 highest import, as in this respect it places 
 the aged nearly on a level with the young, 
 and enables him to read a common print with 
 ease, at a period when, without assistance, 
 he could hardly distinguish one letter from 
 another." — G, Adams on Vision^ 8vo. 1789, 
 p. 105. 
 
 No. II. 
 
 MR. G. ADAMS' OBSERVATIONS ON 
 SHORT-SIGHTEDNESS. 
 
 " It is generally supposed, that the Short- 
 sighted become less so as they advance in 
 years, as the natural shrinking and decay of 
 the humours of the eye lessen its convexity, 
 and thus adapt it better for viewing distant 
 objects : but among the great number of 
 Short-sighted that I have accommodated with 
 
204 APPENDIX. 
 
 glasses, I have ever found the reverse of this 
 theory to be true, and their eyes never re- 
 quired glasses less Concave, but generally 
 more Concave as they grow older, to enable 
 them to see at the same distance." — G. Adams 
 on Vision, 8vo. 1789, p. 126. 
 
 '^ I have found it necessary, in some in- 
 stances, to give Convex Glasses to the Short- 
 sighted when very far advanced in age, not 
 because their Eyes were grown less convex^ 
 but to give them more light, and counteract 
 an extreme contraction of the pupil." — Ibid, 
 p. 127. 
 
 No. III. 
 
 OPTOMETERS. 
 
 Dr. Porterfteld invented an Instrument 
 for measuring the focal distance of the Eye, 
 which he called an Optometer* — See Edinb^ 
 Med. Ess. Vol. IV. p. 85. 
 
 This Optometer has been considerably im- 
 proved by Dr. T. Young, and has been 
 made by Mr. W. Cary, of the Strand, and is 
 easily applicable for the purpose of ascer- 
 taining the focal length of Spectacles re- 
 quired for Myopic or Presbyopic Eyes.— 
 
APPENDIX. 205 
 
 See an Account thereof in Dr. Young's in- 
 teresting Lecture on the Mechanism of the 
 Eye in page 36 of the Phil. Trans. Vol. 
 XCI. 
 
 This ingenious Instrument is a valuable 
 succedaneum to a person residing at a dis- 
 tance from an Optician : — but when the 
 choice of Glasses can be obtained, the plain 
 plan I have laid down in Chapter X. is more 
 accurate, and more satisfactory. 
 
 No. IV. 
 
 DR. SMITH'S RULES FOR CHOOSING SPECTACLES , 
 
 " 51. In order to determine the proper- 
 est Glasses for defective eyes, the distance 
 from the eye, where an object begins to ap- 
 pear confused, should be found — by mea- 
 suring the least distance from which a Long- 
 sighted person can read a newspaper distinct- 
 ly and readily : and likewise by measuring 
 the greatest and the least distances from 
 which a Short-sighted person can read small 
 print readily.'' — Dr. Smith's Optics^ Rem. p. 
 8. 
 
 " Those Glasses are the properest for de- 
 fective Eyes, which are the least Concave^ or 
 18 
 
206 APPENDIX. 
 
 the least Convex of any that will answer the 
 purpose of distinct vision." — Ibid. p. 8. 
 
 " 58. Thus, any person may be fitted 
 with the properest Glasses though he lives at 
 a distance from the shops where they are 
 sold, by sending their focal distances com- 
 puted by the foregoing rules. But if choice 
 of Glasses be at hand, they may be better 
 fitted by trial ; observing only to use those 
 Glasses which are the least Concave or the 
 least Convex of any that will fit the eye. 
 For since they cannot be put quite close to 
 the eye, the less any glass is Concave^ the less 
 it diminishes the pictures of any objects up- 
 on the retina. It will also accustom the eye 
 to that conformation of its coats and hu- 
 mours, which is proper for seeing objects as 
 far off as it can ; and consequently may pre- 
 vent the eye from growing more Short-sight- 
 ed. 
 
 " On the other hand the less any glass is 
 Convex^ the less it magnifies the pictures of 
 objects upon the retina ; and also obliges the 
 eye to that conformation, which is requisite 
 for seeing the objects as near as it can. Both 
 which may prevent the eye in some measure 
 from growing more and more Long-sighted." 
 —page 9. 
 
APPENDIX. 20^1 
 
 No. V. 
 
 Reasons luhy Elderly Persons want Spectacles 
 to read or work with. — By Dr. Jurin and 
 Dr. Smith. 
 
 Indistinctness in Old Men\s Eyes, how 
 
 CAUSED, and how MENDED BY 
 
 Convex Glasses. 
 
 " 88. If the humours of the eye decay- 
 by old age, so as by shrinking to make the 
 cornea and coat of the crystalline humour 
 grow flatter than before, the light will not be 
 refracted enough, and for want of a sufficient 
 refraction will not converge to the bottom of 
 the eye, but to some place beyond it — and 
 by consequence will paint in the bottom of 
 the eye a confused picture ; and according 
 to the indistinctness of the picture, the ob- 
 ject will appear confused. This is the rea- 
 son of the decay of sight in old men, and 
 shews why their sight is mended by Specta- 
 cles. For the Convex glasses supply the de- 
 fect of plumpness in the eye, and by increas- 
 ing the refractions make the rays converge 
 sooner, so as to convene distinctly at the bot- 
 
^08 APPENDIX. 
 
 torn of the eye, if the glass has a due degree 
 of convexity. 
 
 '^ 89. The contrary happens in Short- 
 sighted men whose eyes are too plump. For 
 the refraction being now too great, the rays 
 converge and convene in these eyes before 
 they come to the bottom, and therefore, the 
 picture made in the bottom, and the vision 
 caused thereby, will not be distinct, unless 
 the object be brought so near the eye, as 
 that the place where the converging rays 
 convene mj^y be removed to the bottom, or 
 that the plumpness of the eye be taken off, 
 and the refraction diminished by a concave 
 glass till it come to a due figure." — Dr. 
 Smith's Optics^ 4to. Vol. I. pp. 27 and 28. 
 
 " Elderly persons do not see so well at 
 small distances as those of less age. This 
 happens partly from the shrinking, and part- 
 ly from the rigidity of the Cornea^ which in- 
 creases with our age, and may carry out the 
 nearest limit of Perfect Vision from 3 or 4 
 inches, as in children, and from about 5 or 6 
 inches in youn? adult persons, to 20, 30, 40 
 inches, or a greater distance ; and in this 
 case the eye has no assistance in viewing 
 near objects but only from the contraction of 
 the pupil, and this is not sufficient for Distinct 
 Vision^ unless in a strong light.'' 
 
APPENDIX. 209 
 
 ^' If the arc of the cornea shrink ^^o^h 
 part of an inch, this will remove the natural 
 distance from 15 toll inches: and ihe cornea 
 being now grown more rigid, the uvea will 
 be less able to contract it into a greater con- 
 vexity. While the cornea was more flexible, 
 the uvea was ab!e to render it so convex as 
 to reduce the natural distance from 15 inches 
 to 5, that is to a third part : but now proba- 
 bly the new natural distance of 77 inches 
 can hardly be reduced to less than one half, 
 that is to 38 or 39 inches. 
 
 '^ Now this is probably the case of many 
 persons above 50 years of age, and particu- 
 larly my own, not to have perfect vision at a 
 distance less than :^.8 or 39 inches." — Dr. 
 Jurin's Essay on Vision^ at the end of Dr* 
 Smith's Optics^ p. 148. 
 
 No. VI. 
 
 CURTOUS EXPERIMENT. 
 
 " Into the rin^s of a pair of common Spec- 
 tacles let two pieces of Stained Glass of dif- 
 ferent colours be fixea ; and if these Specta- 
 cles should be worn in the common manner, 
 it is evident, that over one of the retinagwill 
 18 * 
 
210 APPENDIX. 
 
 be diffused rays which excite some other 
 colour : and the consequence will be, that 
 neither colour will be singly perceptible, but 
 that some internnediate colour will be seen. 
 — If the Eyes are alternately closed, so as 
 to exhibit the Two Colours singly, one suc- 
 ceedirig the other, — and immediate y after 
 both Eyes be kept open, the intermediate 
 colour wilt be very perceptible/' 
 
 " If a Blue and a Yellow glass are placed 
 one hef'jre the other, and applied to one Eye, 
 the appearance will be that of a full Green ; 
 but if the same glasses should be applied 
 one before each Eye, as in the experiment 
 of the Spectacles or tubes, the colour will 
 be Green diluted with much white light, or a 
 pale Green ; for when the Glasses are placed 
 one before the other, the two in this position 
 intercept much more light than when they 
 are separate ; and this for a reason which 
 must be obvious to all who are acquainted 
 with Optics. — Dr. Crisp on Vision^ 8vo. 
 1796, pp. 161 and 166. 
 
APPENDIX. 211 
 
 No. VII. 
 
 DR. WELLS ON THE CHANGES WHICH THE 
 VISION OF SHORT-SIGHTED PERSONS UN- 
 DERGOES FROM AGE. 
 
 " It has been very generally, if not uni- 
 versally, asserted by systematic writers up- 
 on Vision, that the Short-sio;hied are render- 
 ed by Age fitter for seeins: distant objects 
 than they were in their Youth. But this 
 opinion appears to me unfounded in fact, and 
 to rest altogether upon a false analogy. If 
 those who possess ordinary Vision, when 
 young, become, from the flatness of the 
 cornea, or other changes in the mere struc- 
 ture of the eye, Long-sighted as they ap- 
 proach to old age, it follows, that the Short- 
 sighted must, from similar changes, become 
 better fitted to see distant objects. Such ap- 
 pears to have been their reasoning. But the 
 course pursued by nature seems very diffe- 
 rent from that which they have assigned to 
 her. For, of four Short-sighted persons of 
 my acquaintance, the ages of whom are be- 
 tween fifty-four and sixty years, and into the 
 state of whose vision I have inquired particu- 
 larly : Two have not observed that their 
 
212 APPENDIX* 
 
 vision has changed since they were young, 
 and two have lately become, in respect to 
 distant objects, more short-sighted tha- they 
 were formerly. As the manner in which 
 this change has occurred is unnoticed, I be- 
 lieve, by any preceding author, I shall here 
 relate the more remarkable of the two cases. 
 " A gentleman became Short-sighted in 
 early life, and as his profession obliged him 
 to attend very much to minute visible objects, 
 he, for many years, wore spectacles with 
 Concave glasses almost constantly, by the 
 aid of which he saw as distinctly, and at as 
 great a variety of distances, as those who 
 €njoy the most perfect vision. At the age 
 of fifty, however, he began to observe 
 that distant objects, though viewed through 
 his glasses, appeared indistinct, and he was 
 hence led to fear, that his eyes were affected 
 with some disease. But happening one day 
 to take up, in an optician's shop, a single con- 
 cave glass, and to hold it before one of his 
 eyes, while his spectacles were on, he found, 
 to his great joy, that he had regained distinct 
 vision of distant objects. With regard to 
 such objects, therefore, he had lately become 
 shorter-sighted than he had formerly been. 
 But along with this change, another occur- 
 red of a directly opposite kind. For when 
 
APPENDIX. 213 
 
 he wished to examine a minute object atten- 
 tively, such as he used to see accurately by 
 means of his spectacles, he now found it ne- 
 cessary to lay them aside, and toemploj^ his 
 naked eye. He had become, therefore, in 
 respect to near objects, longer-sighted. The 
 power, consequently, in this gentleman, to 
 adapt the eye to different distances, is either 
 totally lost or much diminished ; but the 
 point, or small space to which his perfect vi- 
 sion is now confined, instead of being the 
 most remote to which he could formerly ac- 
 commodate his eyes, as is commonly the 
 case with the ordinarily sighted, when they 
 are becoming old, is now placed between the 
 two extremes of his former range of accurate 
 vision. The eyes of the other short-sighted 
 person, a physician of considerable learning, 
 whose vision has been altered by age, have 
 been affected in a similar manner, but not in 
 so great a degree. 
 
 " The only change which had occurred 
 from age, in the sight of such of my acquaint- 
 ance as were considerably myopic, was a 
 lessening, on both sides, of their range of 
 perfect vision."— -From Dr. Wells, on Vision, 
 in the PhiL Trans. Vol. CI. p. 385. 
 
214 
 
 APPENDIX^ 
 
 No. VIII. 
 
 MR JAMES WARE THE OCULIST'S OBSERVA-- 
 TIONS RELATIVE TO THE NEAR AND DIS- 
 TANT SIGHT OF DIFFERENT PERSONS. 
 From the 103d Vol. of PhiL Trans, p. 31. 
 
 ^' The fact that J^ear-sightedness most com- 
 monly commences at an early period of life^ 
 and Distant-sightedness generally at an ad- 
 vanced age, is universally admitted. Near- 
 sightedness generally comes* on between the 
 ages of ten and eighteen. The discovery of 
 it most commonly arises from accident ; and, 
 at first, the inconvenience it occasions is so 
 little, that it is not improbable the imperfec- 
 tion would remain altogether unnoticed, if a 
 comparison were not instituted with the sight 
 of others, or if the experiment w^ere not made 
 of looking through a Concave glass." 
 
 " It should be remembered, that for com- 
 mon purposes every Near-sighted Eye can 
 see with nearly equal accuracy through two 
 glasses, one of which is one number deeper 
 than the other ; and though the Sight be in 
 a high degree more assisted by the deepest 
 
 ^ It is generally observed as soon as persons begin t© 
 use their Eyes in earnest, —-W. K,-~ 
 
APPENDIX. 215 
 
 of these than by the other, yet, on its being 
 first used, the deepest number always occa- 
 sions an uneasy sevisation, as if the Eye was 
 strained- If, therefore, the glass that is most 
 concave be at first employed, the Eye, in a 
 little time, will be accommodated to it, and 
 then a glass one number deeper may be used 
 with similar advantage to the Sight ; and if 
 the wish for enjoying ihe most perfect vision 
 be indulged, this glass may soon be changed 
 for one that is a number still deeper, and so 
 in succession, until, at length, it will be diffi- 
 cult to obtain a glass sufficiently concave to 
 aftbrd the assistance that the Eye requires.* 
 p. 34. 
 
 " Although old persons lose the power of 
 distinguishing correctly near objects, and re- 
 quire for this purpose the aid of convex 
 glasses, they usually retain the sight of those 
 that are distant, as well as when they were 
 young. Instances, however, are not want- 
 
 * I have observed, that most of the Near-sighted per- 
 sons with whom I have had an opportunity of conversing, 
 have had the right eye more near-sighted than the left ; 
 and I think it not improbable, that this difference between 
 the two eyes has been occasioned by the habit of using a 
 single concave hand-glass ; which, being most commonly 
 applied to the right eye, contributes, agreeably to the re- 
 mark above-mentioned, to render this eye more near-sight- 
 ed than the other. 
 
216 APPENDIX. 
 
 ing, of persons advanced in life, who require 
 the aid of convex glasses to enable them to 
 see near, as well as distant objects, p. 43. 
 
 " My own case," Mr. Ware observes, 
 "militates against the common observation, 
 that, as Near-sighted persons grow older they 
 become less Near-sighted ; since my Eyes, 
 on the contrary, are more Near-sighted, at 
 the age of fifty-five, than they were at tw' en- 
 ty-five, and I am now obliged to employ 
 deeper concave glasses than I then used to 
 see distant objects, though I am not able to 
 see distinctly through them things that are 
 near. 
 
 " The alteration which has taken place in 
 my range of vision, 1 have reason to believe, 
 is not unusual. — The following is an instance 
 of this kind, that is still more remarkable. 
 Mr. L., sixty-six years of age, who has spent 
 a great part of his life in the West Indies, 
 and whose sight, when he was young, ena- 
 bled him to see both Near and Distant ob- 
 jects with great precision, began, at the age 
 of forty, to experience a difficulty in reading 
 and writing. He immediately procured con- 
 vex Spectacles of the first number sold by 
 Opticians, w^iich glasses are usually ground 
 to a focus of forty-six* or forty-eight inches, 
 
 * Bead thirty-six,— W^, K. 
 
APPENDIX. 
 
 217 
 
 mid by the aid of these he continued to read 
 and write with ease (distinguishing perfectly 
 in the usual way all distant objects without 
 them,) until he was fifty. At this time he 
 first began to perceive an indistinctness in 
 the appearance of things at a distance ; and, 
 on trying with different glasses, he discover- 
 ed that, by looking through a double-concave 
 glass of the sixth number, (which is ground 
 to a radius of eight inches on one side and 
 eleven inches on the other,) he was enabled to 
 see distant objects distinctly. He has continu- 
 ed to use glasses of this description, for the 
 purpose of seeing distant objects, from that 
 time to the present; but is obliged to remove 
 them whenever he reads, and still to employ 
 the first number of a convex glass. — In this 
 instance a presbyopic was changed to a myo- 
 pic sight, without any known efficient cir- 
 cumstance to produce it. p. 47. 
 
 "' In addition to these cases, I beg leave to 
 add the information I have received from an 
 eminent Mathematical Instrument-maker, 
 about fifty years of age, who has long made 
 use of convex glasses to assist his sight in 
 reading. He tells me, that when he has been 
 employed many hours together, for several 
 successive days, in looking through a double 
 microscope that magnifies twenty-eight times, 
 19 
 
-io APPENDIXe 
 
 (In order to enable him to mark the degrees 
 on a small brass plate,) he has afterwards 
 been able, repeatedly, for a few w^eeks, to 
 read without his glasses ; but then the amend- 
 ment gradually ceases, and he is soon oblig- 
 ed to return to the use of the same .^^lasses 
 that he had worn before*" 
 
 £5* 
 
 No. IX- 
 
 AN APPENDIX TO MR. WARE'S PAPER ON VISION. 
 BY SIR CHARLES BLAGDEN, F.R.S. 
 
 In Vol. 103 of Phil. Trans, p. 110. 
 
 " Mr. ¥/are states in his Paper, that Near- 
 sightedness comes on most frequently at an 
 early age ; that it is more common in the 
 higher than the lower ranks of life ; and that 
 particularly at the Universities, and various 
 colleges, a large proportion of the students 
 make use of concave glasses. All this is ex- 
 actly true, and to be accounted for by one 
 single circumstance, namely, the habit of 
 looking at nefltr objects. Children born with 
 eyes which are capable of adjusting them- 
 selves to the most distant objects, gradually 
 lose that power soon after they begin to read 
 and write : those w^ho are most addicted t<^ 
 
APPENDIX. £19 
 
 Study become Near-sighted more rapidly ; 
 and, if no means are used to counteract the 
 habit, their eyes at length lose irrecoverably 
 the faculty of being brought to the adjust- 
 ment for parallel rays. Of this I am myself 
 an example, and as I recollect distinctly the 
 progress, it may not be useless to record it 
 here. 
 
 " When I first learnt to read, at the usual 
 age of four or five years, I could see most 
 distinctly, across a wide church, the contents 
 of a table, on which the Lord's Prayer and 
 the Belief were painted in suitably large let- 
 ters. In a few years, that is about the ninth 
 or tenth of my age, being much addicted to 
 books, I could no longer read what was paint- 
 ed on this table : but the degree of Near- 
 sightedness was then so small, that I found a 
 watch-glass, though as a meniscus it made 
 the rays diverge very little, sufiicient to en- 
 able me to read the table as before. In a 
 year or two more, the watch-glass would no 
 longer serve my purpose ; but being dissuad- 
 ed from the use of a common conccjve glass, 
 as likely to injure my sight, 1 suffered the 
 inconvenience of a small degree of myopy, 
 till I was more than thirty years of age. 
 That inconvenience, however, gradually 
 though slowly increasing all the time, at 
 
2:20 APPENDIX^ 
 
 length became so grievous, that at two or 
 three-and-thirty, 1 determined to try a con- 
 cave glass: and then found that the numbers 
 2 and 3 were to me in the relation so well 
 described by Mr. Ware ; that is, I could see 
 distant objects tolerably w^ell with the former 
 number, but still more accurately v/ith the 
 latter. After contenting myself a little time 
 with No* 2, I laid it wholly aside for No. 3^ 
 and, in the course of a few more years, came 
 to No. 5, at which point my eye has now 
 been stationary between fifteen and tw^enty 
 years. An earlier use of concave glasses 
 would probably have made me more Near- 
 sighted, or would have brought on my pre- 
 sent degree of myopy at an earlier period of 
 life. If my friends had persuaded me to 
 read and write with the book or paper al= 
 ways as far from my eye as I could see ; or 
 if I had occasionally intermitted study, and 
 taken to field sports, or any employment 
 which would have obliged me to look much 
 at distant objects, it is very probable that I 
 might not have been Near-sighted at all. 
 Possibly the persons who become Near-sight- 
 ed, by having constantly to adjust their eyes 
 to near objects, may not usually change to 
 be Long-sighted by Age." p. 11 L 
 
APPENDIX* ?21 
 
 No. X. 
 
 FROM DR. HERSCHEL'S PAPER ON THE POWER 
 OF PENETRATING INTO SPACE BY TELE- 
 SCOPES. 
 
 [In Vol. XC. of the Phil. Trans, p. 49."] 
 
 " The Aperture of the Pupil of the Eye 
 in different persons differs considerably« Its 
 changes are not easily to be ascertained ; 
 but we shall not be much out in stating its 
 variations to be chiefly between 1 and 2 
 tenths of an inch. Perhaps this may be sup- 
 posed under-rated, for the powers of vision 
 in a room completely darkened will exert 
 themselves in a very extraordinary manner. 
 In some experiments on light, made ai Bath, 
 in the year 1780,1 have often remarked that, 
 after staying some time in a room fitted up 
 for these experiments, where, on entering, 1 
 could not perceive any one object, I was no 
 longer at a loss, in half an hour^s time, to find 
 every thing I wnnted. It is, however, pro- 
 bable that the opening of the Iris is not the 
 only cause of seeing better after remaining 
 long in the dark, but that the tranquillity of 
 the retina, which is not disturbed by foreign 
 objects of vision, may render it fit to receive 
 impressions such as otherwise would have 
 
222 APPENDIX. 
 
 been too faint to be perceived. This seems 
 to be supported by telescopic vision, for it 
 has often happened to me in a fine winter's 
 evening, when at midnight, and in the ab- 
 sence of the Moon, I have taken sweeps of 
 the Heavens, of four, five, or six hours' du- 
 ration, that the sensibility of the Eye, incon- 
 sequence of the exclusion of light from sur- 
 rounding objects, by means of a Black Hood 
 which 1 wear upon those occasions, has been 
 very great ; and it is evident that the open- 
 ing of the Iris would have been of no service 
 in these cases, on account of the diameter of 
 the optic pencil, which, in the 20 feet tele- 
 scope, at the time of sweeping, was no more, 
 than the 12th of an inch. 
 
 ^^ The effect of this increased sensibility 
 was such, that if a star of the 3d magnitude 
 came towards the field of view, I found it 
 necessary to withdraw the eye before its en- 
 trance, in order not to injure the delicacy of 
 vision, acquired by lone continuance in the 
 dark. The transit of large stars, unless 
 where none of the f>th or 7th magnitude could 
 be had, have f^enerally been declined in my 
 sweeps, even with the 20 feet Telescope. 
 And I remember, that after a considerable 
 sweep with the 40 feet instrument, the ap- 
 pearance of Sirkis announced itself at a gr^at 
 
APPENDIX, ^23 
 
 distance, like the dawn of morning, and came 
 on by degrees, increasing in brightness, till 
 this brilliant star at last entered the field of 
 the telescope, with all the splendour of the 
 rising Sun, and forced me to take the eye 
 from that beautiful sight. Such striking ef- 
 fects are a sufficient proof of the great sensi- 
 bility of the Eye acquired by keeping it from 
 the Light, p. 54. 
 
 " On taking notice, in the beginning of 
 sweeps, of the times that passed, I found that 
 the eye, coming from the light, required near 
 20 seconds before it would be sufficiently re- 
 posed to admit a view of very delicate'ob- 
 jects in the telescope ; and that the observa- 
 tion of a transit of a star of the 2d or 3d 
 magnitude would disorder the eye again, so 
 as to require the same time for the re-estab- 
 lishment of its tranquillity. 
 
 "The difficulty of ascertaining the greatest 
 opening of the Eye arises from the impossibi- 
 lity of measuring it at the time of its extreme 
 dilatation, which can only happen when eyt- 
 vy thing is completely dark." 
 
224 APPENDIX* 
 
 No. XI. 
 
 SNOW SPECTACLES. 
 
 These appear as if formed of half the Mar- 
 row-bone of a Leg of Mutton, and are worn 
 by our untutored fellow creatures, to guard 
 their Eyes from the glare of light from the 
 Snow. See page 82. 
 
 The following are the dimensions of a pair 
 which were lent to me, and correspond very 
 nearly with those mentioned at page 99. 
 
 Length of Front 4-j^^ths. 
 
 Breadth across it ly^^ths. 
 
 Distance between the Eye slits Ij^ths. 
 
 The Eye slits m length l^^^ths. 
 
 Ditto m breadth -^^^th. 
 
 The part which answers to the knuckle 
 Troths. 
 
 They are fixed on the head by skin Straps 
 about an Inch broad, which also serve to 
 defend the Eyes from side light. 
 
 THE END* 
 
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HP 
 
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 iiii |i: vi! 
 
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 illiiiii ill \ 
 
 ^ 
 
 I'ip 1 
 
 11 
 
 -|il 
 
 ft^iH 
 
 ^^ '^ '' 
 
 p|| 
 
 ^ ':i 
 
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 B 
 
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Sot o IP -all ^ iLo 
 
 I ogg-nTTX P Blla >lxnnTn 
 

 it J, itJ 
 
 \ 
 
 m 
 
 l®;~ w. 
 
 m 
 
 ,P 
 
 
 m 
 
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 — !^j — ra^l — 
 
 M-A 
 
^^^'^/?iF- 
 
 cor 
 
 ocr '.y 
 
 
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 (I 
 
i 
 
\ 
 
AVIS AU RIELIEUR 
 
 I^ rilieur aura soin de placer le$ gravured, 
 mivant cette table. 
 
 PEEMiEK volum:£:. 
 
 I Plan de Rome ancienne p. xi. 
 % Plan de Rome moderne p. xiii. 
 
 3 Place Colonne p» si. 
 
 4 Temple d'Antonin le Pleux p. 3i« 
 6 Palais Buonaparte au Cours p. 58. 
 
 6 Gapitole p. y^* 
 
 7 Forum Remain p. liii. 
 
 8 J^glise de St. Theodore p. i38. 
 
 9 Temple d'Antonin et Faustine p. lifi*. 
 10 Basilique de Constantin p. 14^. 
 
 J I Temple de Venus et de Rome p. iio» 
 
 la Golisee p. i63. 
 
 i3 Interieur du Golisee p. 168. 
 
 14 Basilique de St. Jean de Latran p. i8i, 
 
 i5 Interieur de St. Jean de Latran p. i83. 
 
 16 Amphitheatre Castrense p. 193. 
 
 in Basilique de Ste. Croix en Jerusalem p. 190. 
 
 18 Monument de I'eau Claudienne p. 194. 
 \ig Minerva Medica p. 197- 
 leo Basilique de Ste. Marie Majeure p. ao8» 
 lai Interieur de Ste. Marie Majeure p. 209. 
 
 i^a Thermes de Diocletien p* 233. 
 
 a3 Place d'Espagne p. 281. 
 !23 Fontaine de Trevi p. qZ%. 
 JaS Golonne Trajane p. 298. 
 
 26 Forum Palladium p. 3 14. 
 
 27 Plan du Pantheon p. 332. 
 
 28 Vue du Pantheon p. 332. 
 
 .^9 Interieur du Pantheon p. 33€. 
 
700 
 
 SECCI7D VOLUME. 
 
 3o Place Navone p. 365. 
 
 3i Palais Massimi p. 373. 
 
 3a Plan du Theatre de Marcellus p. 385. 
 
 33 Theatre de Marcellus p. 385. 
 
 34 Janus Quadrifrons p. 388. 
 
 35 Thermes de Caracalla p. 4^a. 
 
 36 Arc de Drusus p. 411- 
 
 87 Cirque de Romulus dit de Caracalla p. 4^0 
 
 38 Tombeau de Cecile Metella p. 4^3. 
 
 89 Temple de Bacchus p. 4^6. 
 
 40 Plan de St. Paul hors des murs p. 43o. 
 
 4c Basilique de St. Paul p. 480. 
 
 4a Interieur de St. .Paul p. ^3i, 
 
 43 Pyramide de C. Cestius p. 436. . 
 
 44 Temple de Vesta p. 446* 
 
 45 Chateau St. Ange p. 5or. 
 
 46 Plan de St. Pierre au Vatican p. 607, 
 
 47 Basilique de St, Pierre p. 5ii. 
 
 48 Interieur de St. Pierre p. 5 19. 
 
 49 Escalier principal du Musee p. 6^4' 
 
 50 Chambre de la bigue p. 6a6. 
 
 5 1 Pont Mammolo p. 648. 
 5a Tombeau des Plautii p. 65a. 
 
 53 Temple dit de Vesta a Tivoli p. 660. 
 
 54 Grotte de Neptune p. 661. 
 
 Die a8 August! i8a6. 
 
 REIMPRIMATUR 
 
 Fr* Dominicus Buttaoni Rev. Mag. S. P. A 
 Socius. 
 
 REIMPRIMATUR 
 
 f, Delia Porta Patriarch » Constant, ac Vll 
 cesgerens. 
 
XIX 
 
 CHRONOLOGIE 
 DES EMPEREURS ROMAINS. 
 
 Octavien Aiiguste fonde Vempire apres les ^'i- 
 ctoires de Philippes et d'Actium Van 3o avant 
 Vere chretienne 5 et apres avoir ragne 44 ^^^^ 
 il meurt , laUsant Vempire a Tib ere. 
 
 J^re chrSt. 
 Ans 
 
 t4 Tibere. 
 87 Caligula. 
 4 1 Claude. 
 54 Neron. 
 
 68 Galba. 
 
 69 Othon. 
 69 Vitellius. 
 69 Vespasien. 
 79 Titus. 
 
 8r Domitien, 
 
 96 Nerva. 
 
 98 Trajan. 
 117 xldrien. 
 1 38 Antonin le Pieux. 
 161 Marc-Aurele 5 et Lucius Verus. 
 180 Commodea 
 193 Pertinax. 
 193 Didius Jullanus. 
 193 Septime Severe. 
 
 198 Antonin Caracalla ^ et Geta son frere. 
 ^17 Macrin. 
 aiS Heliogabale. 
 iii>a Alexandre Severe. 
 a35 Maximin I. 
 a37 Gordien I et Gordien II. 
 a37 Maxime et Balbin. 
 2.38 Gordien III. 
 ^44 Philippe le pere et le fils. 
 ^49 Deciu§. 
 
XX. Chronologie des Empereurs. 
 
 2,5 1 Gallus et Volusien. 
 
 253 Emilien. 
 
 2.53 Valerien. ^ 
 
 ^53 Gallien. 
 
 368 Claude II. 
 
 ayo Aurelien. 
 
 S175 Tacite et Florien, 
 
 376 Probus. 
 
 aSii Garu3, 
 
 2i83 Garin et Numerien. 
 
 i284 Diocletien. 
 
 a86 Maximien. 
 
 305 Constance Chlore , et Maximien Galere* 
 
 306 Constantiii le Grand. 
 3o6 Maxence. 
 
 3o8 Maximin II. 
 
 3o8 Licinius. 
 
 337 Constantin le jeune^ Constance, et Constant, 
 
 36i Julien. 
 
 363 Jovien. 
 
 3-64 Valentinien I^ et Valent. 
 
 S67 Gratien. 
 
 375 Valentinien IL 
 
 379 Theodose I. 
 
 383 Arcadius. 
 
 393 Honoiius. 
 
 402, Theodose IL 
 
 42.1 Constance II. 
 
 42.5 Valentinien III. 
 
 4'5o Ma^rcien, 
 
 455 Avitus. 
 
 457 Majorien et Leon. 
 
 461 Lybius Severe. 
 
 467 Antheme. 
 
 472. Olybrius. 
 
 473 Glycerins. 
 
 474 Nepos et Zenon. 
 
 475 Romulus 5 ou Augustule qui Pannee suj- 
 
 vante fut detrone par Odoacre Roi des He- 
 rules, Avec luifinitrEmpire d'Occidenc, 
 
 I 
 
XXI 
 
 CHRONOLOGIE 
 
 DES PAPES 
 
 Depuis St. Pierre jusqu'a nos jours. 
 
 JEre chret. 
 
 Ans 
 
 54 St. Pierre de Bethsais en Galilee ^ etablit 
 le siege a Romec 
 
 65 Lin Toscan. 
 
 78 Clet 5 ou Anaclet Athenien. 
 
 91 Clement I Remain. 
 
 96 Evariste Grec. 
 108 Alexandre I Romain, 
 119 Sixte I Remain. 
 ia8 Telesphore Grec. 
 1S9 Hygin Atenien. 
 142. Pie I Aquileien. 
 
 167 Anicet Syrien. 
 
 168 Soter^ de la Gampanie. 
 177 Eleuthere Grec. 
 
 193 Victor I Africain. 
 ao2, Zephyrin Remain. 
 2,18 Gallixte I Remain. 
 22.3 Urbain I Remain. 
 2,3o Pontien Remain. 
 
 235 Antb^re Grec. 
 
 236 Fabien Remain. 
 aSe Cernelius Remain. 
 262, Luce I de Lucques. 
 a53 Etienne I Remain. 
 aS? Sixte II Athenien. 
 ^69 Denis Grec. 
 
 269 Felix I Remain. 
 ii75 Eutychien Toscan. 
 2i83 Gains Dalmate. 
 296 Marcellin Remain. 
 3q3 Marcel I Remain. 
 
XXII Chronologie des Papes. 
 
 3io Melchiade Africain. 
 3(4 Sylvestre I Remain, 
 
 336 Marc I Remain. 
 
 337 Jules I Remain. 
 352. Libere Remain, 
 355 Felix II Remain. 
 366 Damase I EspagnoL 
 385 Sirice Remain. 
 
 898 Anastcrse I Remain. 
 401 Innecent I d'Albano. 
 
 417 Zosime Grec. 
 
 418 Boniface I Remain. 
 
 4^^ Geiestin I de la Gampanie. 
 
 482, Sixte III Remain. 
 
 44e Leon I oil le Grand ^ Toscan. 
 
 461 Hilaire de Sardaigne. 
 
 468 Simolice Tiburtia. 
 
 483 Felix III Remain. 
 
 49a Gelase I Africain. 
 
 496 Anastase II Remain. 
 
 498 Symmac{U0 Remain. 
 
 5i4 Hormisdas de Frosinone. 
 
 52.3 Jean I Toscan. 
 
 52-6 Felix IV Samnite. 
 
 53o Boniface II Remain. 
 
 532, Jean II Remain. 
 
 535 Agapit I Remain. 
 
 536 Sylvere de Frosinone. 
 538 Vigile Remain, 
 
 555 Pelage I Remain. 
 
 56o Jean III Remain. 
 
 574 Benoit I Remain. 
 
 578 Pelage II Remain. 
 
 590 Gregeire I on le Grand ^ Remain, 
 
 604 Sabinien de Blere, 
 
 607 Boniface III Remain. 
 
 608 Boniface IV des Marses. 
 6i5 Deusdedit Remain. 
 
chronologic dos Papes, xxiii 
 
 619 Boniface V Napolitaln. 
 
 6ii5 Honorius I de la Gariipariie. 
 
 640 Severin Romain. 
 
 640 Jean IV Dalmate. 
 
 64^1 Theodore Grec» 
 
 649 Martin I de Todn 
 
 655 Eugene I Romain. 
 
 657 Vitalien de Segni. 
 
 6^2* Adeodat Romain. 
 
 676 Domnus I Romain. 
 
 678 Agathon Sicilian. 
 
 682. Leon II Sicilien. 
 
 684 Benoifc II Romain. 
 
 685 Jean V Syrien. 
 
 686 Conon Sicilien. 
 
 687 Serge I Syrien. 
 701 Jean VI Grec. 
 7g5 Jean VII Grea. 
 708 Sisinnius Syrien. 
 708 Gonstantin Syrien. 
 7i5 Gregoire II Romain. 
 781 Gregoire III Syrien. 
 741 Zacharie Grec. 
 
 75i2. Etienne II Romain. 
 757 Paul I Romain. 
 768 Etienne III Sicilien. 
 7712. Adrien I Romain. 
 795 Leon III Romain. 
 
 816 Etienne IV Romain. 
 
 817 Pascal I Romain. 
 824 Eugene II Romain. 
 82-7 Valentin Romain. 
 8i27 Gregoire IV Romain. 
 844 Serge II Romain. 
 847 Leon IV Romain. 
 855 Benoit III Romain. 
 858 Nicolas I Romain. 
 867 Adrien II Romain. 
 872. Jean VIU Romain. 
 
XXVI Chronologie des Papes* 
 
 1^276 Jean XIX, ou XXI Portugais. 
 
 liiyy Nicolas III Ursin ^ Rornain. 
 
 is8i Martin IV de Montpince. J 
 
 i2<85 Honorius IV Sas?elli y Rorriain, 
 
 liiSy Nicolas IV d'Ascoli. 
 
 laga Celestin V Napolitain. 
 
 1294 Boniface VIII Ca'etani^ d^Anagni. 
 
 i3o3 Benoit XI Boccasini ^ de Trevise. 
 
 i3o5 Clement V de Gouthy Gascon. 
 
 i3i6 Jean XXII d'Euse^ de Quercy. 
 
 1834 Benoit XII Fournier ^ du pays de Foix. 
 
 1842. Clement VI Limousin. 
 
 i35a Innocent VI Limousin. 
 
 i36a Urbain V de Grimoard de Grissae ^ du Ge- 
 
 vaudan. 
 i38o Gregoire XI Limousin. - 
 
 iSgS Urbain VI Prignani , Napolitain. 
 1899 Boniface IX Tomacelli ^ Napolitain. 
 1404 Innocent VII Melioratij Abruzzois. ::^' 
 1406 Gregoire XII Corario ^ Venitien. - * 
 
 1409 Alexandre V Philarge ^ Cretois. 
 
 1410 Jean XXIII Cossa ^ Napolitain. 
 1417 Martin V Colonna , Romain. 
 i43i Eugene IV Condolmere ^ Venitien. 
 1447 Nicolas V de Sarzane. 
 
 1455 Calixte III Borgia y Espa^noL 
 
 145B Pie II Piccolomini , Siennois. 
 
 1464 Pdul II Barhoy Venitien. 
 
 1471 Sixte IV de la Roi^ere , de Savone. 
 
 1484 Innocent VIII Cibo de Melfe^ Genois. 
 
 149a Alexandre VI Lenzoli-Borgia , Espagnol. 
 
 i5o3 Pie III Todeschini'-Piccolomini ^ Siennoi$« 
 
 i5o3 Jules II de la Rovere^ de Savone. 
 
 i5i3 Leon X de Medicis ^ Florentin* 
 
 iSaa Adrien VI Florent ^ Hollandais. 
 
 i5a3 Clement VII de Medicis y Florentin. 
 
 1534 Paul III Farnese y Romain. 
 
 i55o Jules III Giocchi del Monte ^ Romain. 
 
 i555 Marcel II Cervin^ de Fano, 
 
 li 
 
Chronologie des Papes. nxwi 
 
 i555 Paul IV Caraffa ^ Napolitain, 
 
 iSSf) Pie IV Medickini ^ Milariais. 
 
 i566 Pie V Guislieri ^ de Ligurie- 
 
 iSya Gregoire XIII Buoncompagni , de Bologne. 
 
 i585 Sixte V Peretti^ de la Marche d'Ancone. 
 
 2690 Urbain VII Castagno j Genois. 
 
 jSgo Gregoire XIV Sfrondati ^ Cremonais. 
 
 1 59 1 Innocent IX Facchinetti , de Bologne. 
 
 1592. Clement VIII Aldohrandini^ Florentin. 
 
 i6o5 Leon XI de Medicis d'Otto'iano ^ Florentin. 
 
 j6o5 Paul V Borghese ^ Siennois. 
 
 i6i2i Gregoire XV Ludovisi ^ de Bologne. 
 
 3 6:z3 Urbain VIII Bcirberini , Florentin. 
 
 1644 Innocent X Pamphile^ Remain. 
 
 2655 Alexandre VII Chigi ^ Siennois. 
 
 3667 Clement IX Rospigliosi ^ Toscau. 
 
 3670 Clement X Altieri ^ Remain. 
 
 1676 Innocent XI Odescalcid ^ Milanais. 
 
 3689 Alexandre VIII Ottohoni^ Venitien. 
 
 1 69 1 Innocent XII Fignatelliy Napolitain. 
 
 1700 Clement XI Albani^^ du duche d'Urbin. 
 
 I7i2i Innocent XIII Conti ^ Remain. 
 
 5734 Benoit Xill Ursin^ Romain. 
 
 3730 Clement XII Corsini^ Florentin. 
 
 1740 Benoit XIV Lambertini ^ de Bologne. 
 
 3753 Clement XIII Rezzonico ^ Veiaitien. ' 
 
 1769 Clement XIV Ganganelli , de St. Ange de 
 
 Vado. 
 3775 Pie VI Braschi , de Cesene. 
 3800 Pie VII Chiarainonti y de Cesene. 
 1823 Leok XII des comtes de la Genga^ (jiie 
 
 Dieu conserve pour toujour^* 
 
CATALOGUE CHRONOLOGIQUE 
 DES ARTISTES PLUS GjfeLlfeBB.ES 
 
 HOMMES DAITS GET OUTRAGE. 
 
 PEINTRES. 
 Naissance Mart 
 
 2 2i3o Cimabue, Florentin. 
 
 1^76 Giotto de Bondonej Florentin, 
 
 1405 Masaccioj Florentin. 
 
 142.1 Gentil Bellini, Venitien. 
 
 142.4 Jean Bellini^ Venitien. 
 
 1430 Andre Mantegne 3 de Padoue. 
 
 1446 Pierre Vannucci , dit le Perousin 5 de 
 Citta della Pieve. 
 
 1452. Leonard 5 de Vinci en Toscane. 
 
 J454 Bernardin Pinturicchio , de Perouse. 
 
 1469 Frere Barthelemi de St. Marc^ Flo- 
 rentin. 1617 
 
 1471 Albert Purer 5 de Nuremberg. i5sS 
 
 1474 Michel Ange Buonarroti , Florentin. 1664 
 
 1477 Titien Vecelli ^ Venitien. 1676 
 
 1478 George Barbarelli 5 dit le Giorgione ^ 
 
 de Castelfranco. i5ii 
 
 1479 Jean Antoine Razzi 3 de Verceil^ dit 
 
 le Sodome, i554 
 
 1481 Balthasar Peruzzi 5 Siennois. j536 
 
 1481 Benvenuto Tifi, A\X.\q Garofalo ^ de 
 
 Ferrare. i559 
 
 1483 Raphael Sanzio ^ d'Urbin. iSao 
 
 1484 Jean Antoine Licinius^ dit le Por- 
 
 denon ^ Venitien. i54o 
 
 1485 Sebastien del Piombo ^ Venitien. 1647 
 1488 Jean Frangois Penni 5 difc le Fattore ^ 
 
 Florentin. i5:a8 
 
 1488 Andre del Sarto^^ Florentine i53o 
 
From the New York Commercial Advertiser. 
 To my friend C COLUMBUS CON WELL, M. D. on 
 his departure for Rome. 
 b champ^ de 1' Italie, O cainpagnes de Rome, 
 oh dans tout son orgueil git le neant del' hommel 
 C est \k que des aspects I'ameux par les grands noms, 
 Pleins de grands souvenirs, et de hautes lecons, 
 Vous offrent ces objets, nesors des paysages! 
 
 jUbbee de Jardins^ Chant. 4. 
 Thou art going hence, companion, to the old and mighty 
 
 world; 
 To read the records of the past, where glory's wing was 
 
 fuil'd: , 
 
 Where the sanctity a,nd beauty which thy classic page hatli ■ 
 told, ^ 
 
 Will shed their influence on thy heart— a lengthened scroll 
 
 unrolled. 
 Thou wilt roam tlie seven hill'd city, where childhood-tho'ts 
 
 have been; 
 Where the visions of thy withered years have dwelt on eveiy 
 scene. 
 
 Where the. palace of the Caesars will win the musing eye; 
 
 Wliere the mighty spirits of the pasi have hallowed earth 
 '\xi<X sky. 
 
 Thou wiit njark ftalia's palaces— the towering shrines of 
 fame, 
 
 Where the pictured wall will bring tlie speli<of many a glo- 
 rious name; 
 
 And on the Aino's bosom, and o'er the Tiber's yellow tide, 
 
 Thy bark, beneath the purp sky, careeriugly will glidel 
 
 Andfhespirit'sinward questionings will sanctify each pile— 
 Each dome on ponderous columns rear' d— each proud mo- 
 
 nasiic aisle: 
 Where the dim and struggling sunbeam thro' the oriel stains 
 
 Will come; 
 And monument and cf^'/^ph look pale in chastening gloom; 
 While the owi upou the; Palatine, will wave tlie dusky wing. 
 The voice that stirs the ear of night will break thy slumber- 
 ing. 
 
 Thou wilt mark the starlight trembling o'er the colliseum's 
 
 wall; 
 The moonbeam, coloring ivy caves with silvery coronall 
 And, as the golden sunset will tinge Soracte's brow, 
 And the wide Campagna's waste grow dim, as days' warm 
 
 glories go, 
 How will thine ardent spii it grow holy in such hours. 
 As thy dreams warm, thro' faded years, witli all their spells 
 
 and powers! 
 
 And, as from towering mountains there seems a heaven at 
 hand — 
 
 So will thine earnest thoughts draw near the past— the Spi- 
 rit's land. 
 
 Oh, for one brief hour by thee, when thus thy heart is blest; 
 
 One hour, to linger o'er the graves wliere buried empiies 
 rest. 
 
 CJo friend! thou young enthusiast!— joy's cynosure bethin\^ 
 
 And be this strain an offering at friendship's holv shrin^ 
 
 VV. G. 
 Philadelphia, Sept. 3, 1820. ; , ^ 
 
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