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thereby kept in continual agitation: to these evils we may add the dazzling glare and irregular reflexion from the surface of the Glass, which so weakens the Eyes, that those who accustom themselves to a Reading-Glass, are in a short time obliged to take to Spectacles, and to use them 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 will (generally) require Glasses of a different focus for each Eye.

When You go to an Optician's to choose Spectacles, the first thing to attend to, is to look at a Book with each eye alternately, and carefully ascertain, if You see equally well, with both Eyes, with the same Glass, at exactly the same distance.

Inequality of the focus of the Eyes, is much more common than is generally supposed, as Watchmakers, Engravers, and most Artists who work with a Magnifier, will tell you; they generally work with One and the same Eyewith 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 Hearing, and of Seeing, begin to fail about the same time; there are few 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 useless. This fact, is so little known, that I have frequently heard persons who up to the age of 40 have worked their Right Eye-and finding it begin to fail, say, they must begin to teach their Left Eye to See however, as I told them, they found on trial, that the Eye which had been Idle, was much more impaired than that which had been active.

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66 By ceaseless action 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.

* To ascertain whether an Object seen with Both Eyes, appears brighter or larger, than when seen with One Eye

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); 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.

A Single Glass, set in a smart Ring, is often used by Trinket-fanciers merely for Fashion's sake, by folks who have not the least defect in their Sight, and are not aware of the mischievous consequences of such irrita

only, Dr. Jurin made several experiments, which are too long to insert more than the results of them.

"This difference was most conspicous, when in making the experiment by candle-light, the book was 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. - See Dr. SMITH'S Optics, 4to, vol. ii. p. 107 of Remarks.

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"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 One Only."— See Dr. PRIESTLEY on Vision, 4to. 1772, p. 669.

tion: this pernicious plaything will most assuredly, in a very few Years, bring on an imperfect vision in One or Both Eyes.

Notwithstanding all the experience collected 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 little understood, as that of communicating to our speedily perishing 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 Alertness of Youth?

The only way that Persons can indulge their humour of appearing Purblind with impunity,

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CHAPTER II.

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 acquaintance talk of how charmingly 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 assistance, yet, without trying all sorts of Glasses, cannot be convinced, that however this branch of Optics 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, although so serviceable to a person who is deaf, is not of the least use to one who is not deaf.

"I was well-wished to be

Whose Epitaph is better-Took Physic-and Died."

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