Spectacle secrets / [George Cox].

  • Cox, George
Date:
[1844]
Catalogue details

Licence: Public Domain Mark

Credit: Spectacle secrets / [George Cox]. Source: Wellcome Collection.

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    pursuits, are beginning to feel a want of assistance, should have spectacles of sixty-inch focus, which is an exceed¬ ingly slight magnifying power; and if these are found to be insufficient to afford an agreeable and natural perception (not an enlarged or magnified image of the letters of a book, &c., held in the hand at the distance of twelve or fourteen inches from the eye), then apply those of the next power, viz., forty-eight inches’ focus. If these again are unequal to supply the loss of power or incapacity of the eye to converge the light to a point at the instant it reaches the retina, then lenses of thirty- six inches focus are to be had recourse to; and when these fail to afford agreeable vision, thirty, twenty-eight, twenty-four, twenty, must be progressively adopted, thus gradually descending the scale until the eyes receive such compensation for their progressive decay and loss of power, as spectacles carefully suited to the sight are capable so effectually to supply. The period at which the sight begins to fail does not at all depend on age, but varies in different persons according to the formation of the eyes, the treatment they have received, and the constitutional capability; therefore, the age of the person requiring spectacles gives but a vague general idea to the optician as to what is required, unless other particulars are stated; such as whether glasses have been used before ; the distance at which writing and printing is seen pleasantly without assistance, the focus of those last used, or sending even but a broken piece of the same. “ The proper selection of spectacles for imperfect vision is a point of much deeper importance than is generally believed. An oculist who is only acquainted
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