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ence :- and I believe it is as good a General Rule as can be written; but, as I have ob
to enable those who have undergone the operation of Couching, to see objects at different distances who generally require one pair of Spectacles for near, and another for distant, objects. The foci which are used lie between 6 and 11 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; the operation of couching was successfully performed upon her Eyes, and she recovered the use of them; but it appeared that the Visual Organ (as is usual in such cases) was not completely restored to its primitive condition. Some very singular and unaccountable anomalies in her Vision presented themselves, which not a little puzzled the curious in Physiology and Optics.
"It was ascertained that her Eye was able to define a certain class of very minute objects with abundant accuracy, 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 single letter, but complained that she could see nothing but a heap of odd marks.
"These facts, no less strange than true, naturally excited an intense interest among the Medical Professors and Students; every one was anxious to distinguish himself by
served in the Introduction to this workNo General Rule has more Exceptions.
"No regular estimate can ever be established as an absolute criterion, either of the want of, or for the change of Spectacle Glasses; because, the failure or the strength.
affording a satisfactory elucidation of these inexplicable phenomena.
"A hundred theories were framed every one more ingenious than the other. The Professors VON KRACBRANER, and PUZZLEDORF, favoured their pupils with most excellent lectures on the subject, with which they were greatly edified. However, none of the disputants succeeded in establishing a Theory which met with universal approbation. Many of the vulgar still chose to think that all the said Theories might be liable to the old objection (however satisfactory and plausible they might appear), viz. "That they were not True.'
“Matters were in this state, when a mischievous rogue of an Irish student, who took a singular delight in ridiculing 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 Doublegilt Gingerbread, which so entirely won the Youngster's heart, that he confessed (though with some difficulty) that to the best of his belief, his Sister" Sarah had never learned to Read," but unwilling to acknowledge her ignorance, had made him and all the Family - promise not to tell."
of the Sight, varies so considerably with different people: - several youths under 20 years of Age, have applied to me, who could not see either to read or write, 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 St. Ann's Blackfriars, who died in the Year 1795, having attained the age of 81, could read the small print in a pocket Bible, unassisted by Glasses*, even to the last. He never wore Spectacles, nor wanted any."
"I knew a Gentleman who took the assistance 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 satisfactorily for upwards of 40 years."
"Another Gentleman, now living, with
whom I am well acquainted, did not take to the use of Spectacles until he was 55 years of Age: since that period, his Glasses have been twice or three times changed; and although 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 indebted to MR. SAMUEL PIERCE.
The time that the First Glasses of 36 inches focus will sufficiently assist the Sight - depends on the peculiar nature of the Eyes on the wear they have previously had — on on their subsequent exertions—and on the Constitution 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, seldom 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 Magnifier.
As a general Rule, the first Spectacles will last You for reading by Daylight, during your first apprenticeship to Old Age-i. e. about 7 Years.
WHEN TO CHANGE THE FIRST SPECTACLES, FOR STRONGER MAGNIFIERS.
WHEN You find a recurrence of the Symptoms 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 require The Second Sight of 30 inches focus. - But, I most earnestly entreat my friend the Reader, to be content with as little assistance as will enable him to read a Newspaper comfortably by Candle-light,* at about the same distance he did before his Sight was impaired — from 8
* See Reading Candlestick or Lamp, in the Table of Contents.