54 WONDERS OF LIGHT AND OF COLOUR. If the light be moved from the circumference nearer toward the centre the focus will be farther off. If the light be put closer to the lens than its focus, the rays will be divergent, or spreading. … The above will suffice to illustrate a double convex lens. B is a plano-convex lens, and parallel rays will meet at the circumference (instead of at the centre, as in a) ; and conversely a light at the circumference (which is its focus) will emit parallel rays through this lens.
Light · Color · Optical illusions · Optics
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