The Moving Picture World (April 1907)

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u6 THE MOVING PICTURE WORLD. /. $l,OOCX22 will be paid by the publishers of the Moving Picture World, to any person who can prove that this paper is controlled, subsidised, or financed by any firm, interested in the manu- facture, sale or rental of films, or machines used for the pro- jection of films. Our attention has been called to reports that have been put in circulation maliciously, to the effect that this publication is owned, or controlled, by" Miles Bros., of New York, and that Biograph and Edison Companies are interested therein. We wish to state, that all the control exercised by the above firms is, nil. Their sole interest is in the results that they may obtain from, advertising with us. As keen business men, they gave their sup- port by advertising in an independent paper which will .voice the sentiments of all. Our books are open to the inspection of all advertisers and non-partisan readers to verify our statements, and satisfy themselves of our bona fides. We trust we shall not have to revert to this subject again, and will say in conclusion, using a political phrase, the report is a " boomerang." The Optics of Photographic and Projecting Lenses. Chapter II. REFRACTION OF LIGHT THROUGH ^ PHERI CAL TRANSPARENT SUBSTANCES OR LENSES. By Joseph Menchen. jrXt is to the refraction of light that we are indebted fo the use of lenses or artificial glasses to aid the powers oi vision. It lays the foundation of telescopes, microscopes camera obscuras, phantasmagorias, and other optical struments, by which so many beautiful; useful, and won derful effects have been produced.' In order, therefore to illustrate the principles on which such instruments an constructed, it is necessary to explain the manner which the rays of light are refracted and modified who passing through spherical mediums of different forms. W< do not intend, however, to enter into the minutiae of this subject, nor into any abstract mathematical demonstra tions, but shall simply offer a few explanations of genera principles, and several experimental illustrations, whi may enable the general reader to understand the construe tion of the optical instruments to be afterward described A lense is a transparent substance of a differed density from the surrounding. medium, and terminatinj in two surfaces, either both spherical, or one spherica and the other plain. It is usually made of glass, but maj also be formed of any other transparent substance, as ice, crystal, diamond, pebbles, or by fluids of different den sities and refractive powers, enclosed between concan glasses. Lenses are ground into various forms, accordinj to the purpose they are intended to serve. They may generally distinguished as being either convex or con cave. A convex glass is thickest in the middle, and thinner towards the extremities. Of these there are various forms, which are represented in Fig i. * A is plano-convex lens, which has one side plane, and tin other spherical or convex. B is a plano-concave, whi is plane on the one side and concave on the other. C ii double convex, or one which is spherical on both sides, a double concave, or concave on both sides. E is called a meniscus, which is convex on one side and concave on the other. F is a concavo-convex, the convex side o which is of a smaller sphere than the concave. In regard to the degree of convexity or concavity in lenses, it is evident that there may be almost an infinite variety. F« every convex surface is to be considered as the segment of a circle, the diameter and radius of which may vary to almost any extent. Hence lenses have been formed by opticians, varying from one-fiftieth of an inch in radios to two hundred feet. When we speak of the length of the radius of a lense, as, for instance, when we say that a lense is two inches or forty inches radius, we moan that the convex surface of the class is the Dart of a circle, the