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"Men must be taught as if you taught them not,
Essay on Criticism.
I am sure
I do not think it is Business my it is not my Pleasure, to register the various pretended improvements in Spectacles which have from time to time been proposed to the Public, such as the Sympathetic Pebbleswhich" as the Sight alters, they will alter also to the Sight, by which one pair will last the wearer for Life," &c. &c. &c.!!! This would be irksome to the Writer, and useless to the Reader. I shall only mention the most
In 1758, Mr. B. Martin published a pamphlet recommending what he called
" VISUAL GLASSES,"
the use of which, he assures us, would be "productive of peculiar advantages," — they
but, by Mr. Adam's account, not
to the gentlefolk who bought them.
"The desire men have to increase their
Business, and extend their Fame, has, in many instances, been the origin of alterations and injurious to Science and detri
mental to the Public.
To this we may, with propriety, impute the invention of Visual Spectacles. But the good sense of the world, which always, in the long run, justly appreciates the value of every invention, now leaves Visual Spectacles to the neglect they merit."-G. ADAM'S Essay on Vision, 8vo. 1792, p. 113.
I beg to be excused saying more, than that I do not think that any of the Spectacle Glasses which have come before my Eye, have any superiority over the Common Spherical Lenses now in general use.
In instituting Experiments for ascertaining the distinctness and brightness of Spectacle Glasses-be extremely careful, that the Glass is not only of exactly the same quality, but also of exactly the same Focal length—or any attempt at comparison will be useless.
If one of the Glasses be only of a very little shorter focus than the other-objects will always make a very different, and sometimes a much stronger impression on the Eye.
To measure the Focal Length of Spectacle Glasses, see Chapter xv.
To give my Readers all the satisfaction in my power,-I have added an APPENDIX which contains sufficient corroboration of what I have asserted on certain important points, because by the time Persons want Spectacles, they have generally become wise "in their own conceit," and have picked up a parcel of silly prejudices concerning them, which unless completely counteracted, and rectified by the invariable standard of irresistible Truth, will prevent their deriving that benefit from this publication, which the Author heartily wishes that they should receive to the utmost extent.
I have given Rules for the choice of Glasses as relates to their degrees of Magnifying, and have also pointed out those crite
rions by which All may judge if the Glasses are good and of the right focus and readily discover those imperfections in them which are so common, and so injurious to the Eyes.*
* See Chapter xvii. "Of the Quality of Spectacle Glasses," and the Note at the foot of page 40.
To effectually eradicate erroneous opinions, and to establish the Truth beyond all doubt, I know is no easy task therefore, I have given an Appendix of Quotations from the best Authors on the subject the correctness of whose Judgment has been established by Experiment, and has been pronounced indubitable, by universal acceptance-i. e. from the Writings of Dr. Smith; - Dr. Jurin; Dr. Porterfield;-Dr. Blagden ;-Dr. Wells ;-Dr. Herschell ;- Mr. G. Adams, the Optician;the late Mr. Ware, the Oculist; and Mr. Stevenson, the Oculist; — and for many valuable facts, I am indebted to that experienced Optician, MR. SAMUEL PIERCE, who was upwards of Thirty Years with Mr. Jesse Ramsden.
“Palmam qui meruit, ferat.”
There could not be a more useful Charity – than that of providing proper
SPECTACLES FOR THE POOR.
The Best Glasses, set in Single-Jointed Steel Frames, may be purchased wholesale at the rate of 18s. per dozen Pairs; - if a Singlejointed frame is fastened round the head with
a Riband, it may be kept on, almost as steadily and comfortably as a Double-Jointed Frame.
For the small sum of 18 Pence the Benevolent may enjoy the gratifying reflection of giving an industrious Workman the power of long continuing his labour with undiminished Ability, and of earning a subsistence till extreme Old Age.
In no way-can so much Good be done with so little Money!
"Qui Visum, Vitam dat."
The greatest part of the Disorders of the Eyes of Poor People who are upwards of 45 years of Age, are occasioned by their straining their Sight for want of Spectacles, or by looking through Bad Glasses, or those of a Focus not suitable to their Eyes: - I hope when this is considered by THE OVERSEERS OF THE POOR, THE DISTRICT SoCIETIES FOR BETTERING THE CONDITION OF THE POOR, and the Patrons of THE EYE INFIRMARIES, that they will make the distribution of Spectacles a part of their Bounty.