Ta all who value their sight : a few practical suggestions and illustrations ... / by R.B. Bate.

  • Bate, R. B. (Robert Brettell)
Date:
1830
Catalogue details

Licence: Public Domain Mark

Credit: Ta all who value their sight : a few practical suggestions and illustrations ... / by R.B. Bate. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    so striking, that persons may be well excused for imagin- ing that they see worse without them than before. The strong impression made by the comparative indis- The impres- tinctness of the print, immediately on the removal of their spectacles, alone mduces many to believe that they cannot JJjJ^ 5nionr read without them, particularly if they have long delayed beginning with them; but if such persons, on taking off their spectacles, would give time for the sympathetic action of tlie nerves and muscles, before alluded to, to move the print to such a distance as to suit the focal length of the eye when unassisted, they might feel satisfied that they see the print as well as they did before, because they would then perceive no other impediment than what arises from the diminution of its size by removal, as before described. It must however be admitted, that some ground for which only this prejudice is afforded by the mischief which actually holds against arises from the use of spectacles improperly chosen *; as in the instance of those who, not having access to persons ca- ^ ^ ' pable of or disposed to pay proper attention to their selec- tion, have chosen such as they liked the best, frequently those]which magnified the most. This effect is perhaps more strongly instanced in others, who have adopted the spec- tacles of their deceased friends, the glasses f of which, being commonly too old for the survivors, also magnify too much; and too old. and by their use, the eye, becoming adapted to such glasses, is in some degree incapable of seeing without them.—As it is highly desirable that the occasion of this effect, as well as of the condition which begets the necessity for aid, should be somewhat explained, the reader's attention is requested to the following illustrations, which shall be stripped of tech- nicalities, and made as plain and intelligible as possible. I. _ The ball of the eye is nearly round, and internally Attempt to consists of three transparent humours, distinguished by their explain the supposed resemblance to water, glass, and crystal: upon cause of this, the action % of these depends the focal length of the eye, ♦ These however, being instances of the abuse rather than of the use of spectacles, are no objections to their judicious employment. t It cannot be too generally known, that glasses may be obtained at the best opticians, properly suited to the sight, and fitted to the frame, for 1*. 6rf, and 2s. per pair. 1 To illustrate this, take a magnifying glass into the darkest pai-t of the room, and hold it in such a manner as to let the light fall directly through It on a piece of paper; by moving the glass to and fro, a distance will be tound at which the image of the window will be distinctly seen upon the paper: this distance is the/oca/ length of that glass. If a glass of \