(From conspicio, to behold). Spectacles.

Spectacles are either convex, concave, or plain. The first are adapted to old persons; the next to those who see only with distinctness at a small distance; and the third, formed of glass with a light green or blue shade, are designed to defend weak eyes from too strong light. The form of the eye in old and near sighted people has been explained under the terms Ambly opia; and the subject will again recur, vide Presbytae and Myopes.

Those who wear spectacles should be very cautious. to have the glasses ground with the most perfect accuracy, and should apply to opticians of credit, rather than to itinerant Jews; for the aberrations of the rays produced, by an imperfect figure of the glass, strain the eye to distinguish the image; from this cause indistinct. For a similar reason, the glasses of old people should be not at all, or very slightly, tinged: and the glare which arises from a candle, or a strong sun, may be better avoided by a shade against the former, or over the eyes, to guard against the latter.

It has been doubted whether spectacles should be used to preserve the sight. We think that in old persons they will be useful: with the near sighted, who are usually young, they should be discouraged. Old people will save their eyes, and there is little danger of exhausting the degrees of convexity: indeed none. The young will not, indeed, exhaust the degrees of concavity; but the other senses should be kept "on the alert,"while they can supply the place of distinct vision. The hearing, the feeling, even the facility of conjecture, are kept alive by disusing spectacles; and we should improve all our powers. As we have already hinted, the near sighted person should use the number next below that of distinct vision, and he will soon attain it. Habit, in this way, will coincide with the change which age induces; and not to see with the utmost acuteness, is still an advantage to those who could otherwise see very imperfectly.- All this is, however, refinement; for spectacles used with little caution or discrimination have seldom done harm, if the glasses are good.

Pebbles, which admit not of scratches, should be in every instance preferred.