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serve his Customers, or occasionally to look along the Street for a passing friend. Another pair of deeper focus, was a repeated necessary 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 would not perform their office distinctly, unless assisted by Spectacles of 11 Inches focus so that he became literally half-blind in the course of about 10 Years.
"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 aware of 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 canvas."-MR. S. PIERCE.
With such divided Glasses, it requires considerable 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 moment, — One playing "Sally in our Ally,”— and the Other " Ally Croaker."
There have been several other plans for obtaining the convenience of Two pairs of Spectacles in One frame - by having the glasses to turn up on the side, &c. 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. I 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 Glasses in a frame attached to the Spectacle frame, and moving on hinges which, when brought down before the Glasses
fixed in the Spectacle frame might make combined the focus required for painting the Picture, and which, when it was requisite to refer to the Object or Sketch, might be turned up on the Forehead, quite out of the way.
"The late President of the Royal Academy - BENJAMIN 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 90 years of age, he had the upper half of 30 inches focus, and the under half of only 8 inches focus." The Glasses were round and an inch and a half in diameter.
The above account of Mr. West's Spectacles is another of the contributions of Mr. S. Pierce, who made the Spectacles.
By trying a variety* of Glasses at an Opti
• Though in the choice of Spectacles, every one must finally determine for himself, which are the Glasses
cian's, the Sight soon becomes confused and tired, and for the moment quite unfit to appreciate with proper accuracy, what Glasses 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 Glasses, which consist of Spectacles, of regular gradations of power, set in a framethe first Set of Convexes usually contains the first Seven Glasses mentioned in the Table at page 33 or, if these cannot be had choose at the Optician's, those Spectacles which they
through which he obtains the most distinct Vision; — yet some confidence should be placed in the judgment of the Artist of whom they are purchased, 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 the purchaser often fixes upon a pair of Spectacles not the best adapted to his sight, 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. 1789, p. 96.
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 try these repeatedly for whatever purpose they wish to employ should take care, that the Glasses they
them: 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 magnifying power more than they require by Daylight, will show very small objects most distinctly but I protest against such indulgence at first-when the Sight is much impaired by Age a pair of Glasses for use by Day, and another for Night, are advisable comforts for the Eyes.
The best plan for the Preservation of the Eyes,
is not to employ them in any work at Night
that gives them any trouble: let all Business which requires intense attention, such as mending Pens, &c. be done by "the better Day."