Q. What sort of glasses are double convex spectacle-glasses?
A. Glasses which curve outwards on both sides.
The figure A is double convex, or convex on both sides.
Q. What is the use of double convex spectacle-glasses?
A. As the image of near objects is reflected behind the ret’ina, these double convex glasses shorten the focus of the eye, and bring the image into the eye (upon the ret’ina).
Q. Why do near-sighted persons bring objects close to the eye, in order to see them?
A. As the distance between the front and back of their eye is too great, distant objects are reflected before they reach the ret’ina; therefore, near-sighted persons bring the objects closer, in order that the reflection may be cast further back, (to reach the ret’ina).
Q. Why do old people hold objects further off, in order to see them better?