Isaac Newton

“ This is the reason of the decay of sight in old Men, and shews why their Sight is mended by Spectacles. For those Convex glasses supply the defect of plumpness in the Eye, and by increasing the Refraction make the Rays con­verge sooner, so as to convene distinctly at the bottom of the Eye if the Glass have a due degree of convexity. And the contrary happens in short­sighted Meh whose Eyes are too plump. For the Re­fraction being now too great, the Rays converge and convene in the Eyes before they come at the bottom ”

“ AX VII. AX. VII. Wherever the Rays which come from all the Points of any Object meet again in so many Points after they have been made to converge by Reflection or Refraction, there they will make a Picture of the Object upon any white Body on which they fall.
So if PR [in Fig. 3.] represent any Object without Doors, and AB be a Lens placed at a hole in the Window-shut of a dark Chamber, whereby the Rays that come from any Point Q of that Object are made to converge and meet again in the Point q ”

“ AX. VIII. An Object seen by Reflexion or Refraction, appears in that place from whence the Rays after their last Re-flexion or Refraction diverge in falling on the Spec­tator's Eye. If the Object A [in Fig. 9.] be seen by Reflexion of a Looking-glass mn, it shall appear, not in its proper place A, but behind the Glass at a, from whence any Rays AB, AC, AD, which flow from one and the same Point of the Object, do after their Re-flexion made in the Points B, C, D, diverge in going from the Glass to E, F, G, where they are incident on the Spectator's Eyes. ”