surface, in so much that DR. PETIT found that the Crystalline of a man 81 years old, resembled two pieces of beautiful Yellow Amber."-Dr. PORTERFIELD on the Eye, 1759, 8vo. vol. i. p. 229.

The commencement and progress of the deterioration of the Sight, depends upon the health of the individual upon 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 50, while the Sight of some persons continues almost as perfect at 50 as it was at 30.

The average period of the Eyes requiring Spectacles 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 distinctly 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 degree of Shortness in their sight, which is the cause of their possessing that advantage longer than persons in general do-if they will try that very shallow Concave which is called, by Opticians, "No. O. Concave," or " 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 by 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 be impaired by Age, is that when You wish to read

a small print, 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 double, &c.; and, BY CANDLE-LIGHT,* You catch yourself holding a Book, &c. close behind the Candle- and, that you begin to admire the ingenuity of the Gentleman who invented Snuffers.

You will begin to feel the absolute necessity of using Glasses, when you want to read a small print by Candle-light, for Twelve months before you require their assistance by Day-light. See Cumumbra Lamp.

* "There are many who find the effect of Candle-light 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 maintain their natural Vigour."- Mr. G. ADAMS on Vision, 8vo. 1789. p. 108.

If You obstinately strive against Nature, and barbarously refuse your Eyes that assistance from Art-which will enable You to see with great ease, but without which, you cannot see without great difficulty — 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.

However, some people seem to be about as unwilling to acknowledge this Truth as they are to confess that they do not feel quite so frisky at 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 again:" 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 distinctly, and when they attempt to read without, 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 refusing 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 considerably increased, and the Eyes be weakened by the efforts they are compelled to exert; all delay is dangerous, and the longer those who feel the want of assistance, defer the use of Spectacles, the more they will increase 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 person 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