. The microscope and its revelations. ought by the first lens to a focus two inches behindthe second if it were not there. This point, which is negative withregard to the second lens, must be taken as the value of p in theformula. We have, therefore : -2V / 6 Hitherto our attention lias been confined, in studying the actionof lenses, to the manner in which they act upon a bundle of parallelrays, or upon a pencil of rays issuing from a radiant point. More-over, we have considered this point as situated in the line of the surface of every luminous body may be regarded as compre-hending
. The microscope and its revelations. ought by the first lens to a focus two inches behindthe second if it were not there. This point, which is negative withregard to the second lens, must be taken as the value of p in theformula. We have, therefore : -2V / 6 Hitherto our attention lias been confined, in studying the actionof lenses, to the manner in which they act upon a bundle of parallelrays, or upon a pencil of rays issuing from a radiant point. More-over, we have considered this point as situated in the line of the surface of every luminous body may be regarded as compre-hending an infinite number of such points, from every one of whicha pencil of rays proceeds, to be refracted in its passage through thelens according to the laws enunciated. In this \vay a completeimage, picture of the object, will be formed upon a suitablesurface placed in the position of the focus. There are two kinds of image formed by lenses, a real image anda virtual image. 1. The formation of a real image means the production of a. FIG. 26.—The formation of a real image. picture by a lens, or a combination of lenses, which can be thrownupon a screen ; such are the images of a projection lantern and theimage produced by the camera upon the focussing glass. The mannerin which this takes place will be understood by reference to fig. 26,where A B is an object placed beyond P, the principal focus of theaplaiiatic combination. From every point of A B are rays radiatingat every possible angle. Let AF and AH be two such raysradiating from the point A. Now if the refraction of these rays be 24 ELEMENTARY PRINCIPLES OF MICROSCOPICAL OPTICS traced, in the manner already indicated, through the aplanatic com-bination, it will be found that the rays which before immergencewere diverging are by the refraction of the combination on emer-gence rendered converging. Thus the ray F C meets H C at thepoint C. The point C is called the conjugate focal point of A, andwherever there is a focal po
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
