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No. VI. Curious Experiment

PAGE

....

VII. Dr. WELLS on the Changes which the
Vision of Short-sighted Persons un-
dergoes from Age.....

231

232

VIII. Mr. WARE'S Observations on the Near
and Distant Sight of different Persons 235
IX. Appendix to Mr. WARE's Paper, by
Sir CHARLES BLAGDEN

.....

X. Sir WILLIAM HERSCHEL On the Aper

tures of the Pupil of the Eye

XI. Snow Spectacles....

240

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Explanation of the Plate fronting the Title.

FIG. I. Is the Spectacle front recommended for Eyes in general; the distance between the centres of the openings which hold the Glasses being 2 inches, i. e. 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 81, and No. X. of the Appendix.

FIG. III. The Pupil in its most contracted state. page 81, &c.

See

FIG. IV. Convenient double Folding Hand Spectacles. See page 22.

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 29.

FIG. VI. The 8th Sight, for Long Sighted Eyes - or 12 Inches focus.

FIG. VII. No. 1 CONCAVE, or the First Sight for Short Sighted Persons. See Chapter XIII. page 94.

FIG. VIII. No. 12 Concave, or the 12th Sight for Short Sighted Persons.

The Plate of the Pancratic Eye-Tube and Double Stars

to face page 130.

PREFACE.

TO BE READ AFTER THE WORK.

Now, 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 you so little pleasure, that You begin to think You would rather have your Seven Shillings in your pocket 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 decoyed, 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 Amusement 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 borrowing your New Books, and so contrive to become wise at your expense,but do the Author the favour to recommend all your Friends to purchase it.

B

INTRODUCTION.

GENERAL 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 Genius begins to wait upon Judgment,† the persevering Student would no longer be able to enjoy the fruits of the labours of his Predecessors, or to preserve the produce of his own for the benefit of Posterity.

* "Were there no other use of Optics, than the invention of Spectacles for the help of defective Eyes, I should think the advantage which mankind receives thereby, inferior to no other benefit whatever, not absolutely requisite to support Life.” - MOLYNEUX's Optics.

"The exact time when years have ripened the Judgment, without diminishing the Imagination, by good critics is held to be punctually at Forty."-See MARTIN SCRIBLERUS on the Dunciad, p. 55.

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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 the First period of Life, would very soon after cease to be productive, and, but for the Eyeinvigorating Art of the Optician, his latter 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 most 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 attainable, 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."

It is presumed, that the majority of the purchasers of this Work, cannot See! till they have learned how by the instructions herein given.

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