Outlines of Natural Philosophy for Schools and General Readers baixar o livro de graça

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. 1887 Excerpt: ... layers bounded by the circular arcs in the figure, and the ray to keep a straight course within each layer, but to be bent at an angle in passing from each layer to the next. 194. Prism.--It is easy to produce large changes in the direction of rays of light by employing a prism. All that is really necessary is a piece of glass with two plane faces inclined at a considerable angle to each other; but the prisms commonly employed are triangular (either equilateral or isosceles, ) as in fig. 112, which shows a prism mounted on an adjustable stand, by means of which it can be raised, lowered, and turned about into any position that may be required. When it is placed (as in the figure) with one of its faces (which we shall call the base) horizontal, and one of its three edges at the top, a ray entering at one of the two sloping faces, then traversing the prism to the other sloping face, and there emerging, will be bent down, as shown by the dotted line from the candle to the observer's eye in the figure, and the observer will consequently see the candle lifted up, for it will appear to him to be in the prolongation of the ray which enters his eye. Refraction through Prism. 195. To understand how this is, look at fig. 113, where S I is the incident ray, N I the normal at the point of incidence, IE the course of the ray through the prism, E B the emergent ray, and E N' the normal at the point of emergence. The angle which the ray in the prism makes with the first normal is smaller than the angle of incidence NIS, and the angle which it makes with the second normal is smaller than the angle of emergence N'EB; for the rule always is that the ray in glass makes a smaller angle with the normal than the ray in air. At both faces it is thus bent towards the base of the p...