This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1920 Excerpt: ... bright, the amount of light passing through the hole being great. Further, the image is inverted, since all the beams cross at C. It will also be noted from the geometry of Fig. 491 that the size of the image is proportional to its distance from the pin-hole. If the screen ab be moved nearer to the pin-hole, the image will become smaller and brighter, but it will be noted that it becomes more blurred, owing to the increased overlapping of the patches of light. Exit. 113.--Pin-hole camera. Obtain an ordinary cardboard box; remove one side or end and replace it by a sheet of oiled paper, or ground glass. Make a pin-hole in the side furthest from the oiled paper. On pointing this hole towards the brightly illuminated window of a room, an inverted image of the window and all bright objects near it will be seen on the oiled paper. Transparence, opacity, translucence.--The terms 'transparent' and 'opaque,' as applied to bodies, have been used already, and they may now be defined more exactly. A transparent body is one which will transmit light according to the straight-line law, whereas a body is opaque when it will not transmit light at all. The terms are really only relative, as materials usually considered to be transparent, such as glass, absorb some light when a beam traverses them. On looking through a thick block of glass at a bright object, it will be seen that the brightness is much reduced, and generally the emergent light is of a greenish blue colour. Thus a sufficient thickness of glass would transmit hardly any light. On the other hand, bodies so opaque as the metals will, if sufficiently thin, transmit an appreciable amount of light. Gold may be obtained in such thin layers, in the form of gold leaf, that light will pass through, and the transmitte...
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