. The Pharmaceutical era. Fig. 6.—Convergence of Light hy Convex Lens. If the divergent rays originate within or between theprincipal focus and the lens, they will be divergent afterrefraction, but less divergent than before. The straight line passing through both the principalfocus and the middle of the lens is known as the opticaxis of the lens. What is Magnification ?—A question which naturally sug-gests itself to the student is, Why does an object appearlarger when viewed through a convex lens? This is com-monly answered by the statement that the effect of aconvex lens is to increase the v
. The Pharmaceutical era. Fig. 6.—Convergence of Light hy Convex Lens. If the divergent rays originate within or between theprincipal focus and the lens, they will be divergent afterrefraction, but less divergent than before. The straight line passing through both the principalfocus and the middle of the lens is known as the opticaxis of the lens. What is Magnification ?—A question which naturally sug-gests itself to the student is, Why does an object appearlarger when viewed through a convex lens? This is com-monly answered by the statement that the effect of aconvex lens is to increase the visual angle, i. e., to in-crease the angle of the light rays coming from differentpoints on an object. From the illustration (Fig. 7) it is. Fig. 7.—Effect of ^isual Angle on Size. evident that the angle subtended by the arrow increasesas the eye moves toward it. with an apparent increasein the size of the object. The part played by the, lensis to increase the size of the angle artificially by meansof the property of refraction. By increasing the angle of the rays before they enterthe eye, they cross earlier within the vitreous humor andconsequently the image projected upon the retina islarger. An image formed without the aid of a lens maycover too small a space on the retina to excite the sensa-tion of sight, but by the interposition of a lens a largerretinal surface is covered, and the object becomes visible. Designation of Magnifying Power.—Magnifying power, oramplification, as it is frequently called, is expressed ei-ther as diameters or as times, the former method beingpreferable. When it is said that a given lens magnifiesan object one hundred diameters it is understood that itsapparent length or breadth as seen
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Keywords: ., bookcentury1800, booksubjectdrugs, booksubjectpharmacy, bookyear1
