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able Achromatic adjust aperture appear applied assistance attention become better bright called centre CHAPTER Colour common Concave Convex define diameter distance distant objects distinct distinctly Double Stars Ears easily effect enable equal exactly experience extremely Eye-glass Eye-tube feet field of view Figure focal length frame front give given half happens hold Illuminating inch in diameter inches focus increased Joint larger least less light look Magnifying power manner measure natural night Object Object-glass observed opening Opera Glass Optical Optician original pair Pancratic perfect perfectly perform persons Phil placed position prevent produce proper proportion Pupil rays Reader remarkably require round seen Senses shew Short Short-sighted side Sight Single soon Spectacles Star sufficient Telescope Theatre thing Three tion Trans true tube usual Vision whole wish
Pagina 19 - Why has not man a microscopic eye ? For this plain reason, man is not a fly.
Pagina 197 - And speak, though sure, with seeming diffidence; Some positive persisting fops we know, Who if once wrong will needs be always so; But you with pleasure own your errors past, And make each day a critique on the last.
Pagina 105 - A man of sense sees, hears and retains everything that passes where he is. I desire I may never hear you talk of not minding, nor complain, as most fools do, of a treacherous memory. Mind not only what people say, but how they say it; and if you have any sagacity you may discover more truth by your eyes than by your ears. People can say what they will, but they cannot look just as they will; and their looks frequently discover what their words are calculated to conceal.
Pagina 26 - ... eye than you have been accustomed to do, and desire the aid of plenty of light ; and on looking at a near object, it becomes confused, and appears to have a kind of mist before it, and the letters of a book run one into another, or appear double, &c. ; and BY CANDLELIGHT you catch yourself holding a book &c. close behind the candle.
Pagina 245 - At one time, after sweeping a portion of the heavens with that instrument, he tells us that " the appearance of Sirius announced itself at a great distance like the dawn of the morning, and came on by degrees, increasing in brightness, till this brilliant Star at last entered the field of the telescope with all the splendour of the rising sun, and forced me to take my eye from the beautiful sight.
Pagina 98 - The fact is this, that he does not know a shortsighted person, who has had occasion to increase the depth of his glasses, if he began to use them in the form of spectacles ; whereas he can recollect several instances, where those have been obliged to change their concave glasses repeatedly, for others of higher powers, who had been accustomed to apply them to one eye only.
Pagina 14 - When persons who have long patronized One Eye, and slighted the Other, take to Spectacles, they will (generally) require Glasses of a different focus for each Eye. When You go to an Optician's to choose Spectacles, the first thing to attend to, is to look at a Book with each eye alternately, — and carefully ascertain, if You see equally well, with both Eyes, with the same Glass, at exactly the same distance.