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THE POPULAR EDUCATOR. 



RECREATIVE SCIENCE. XII. 



AMUSING EFFECTS OF EEFRACTION DISSOLVING VIEWS. 



WE now proceed with illusions and instruments in which re- 

 fraction only is used, and not reflection. 



To construct a magic picture which, being seen in a certain 

 point through a glass, shall exhibit an object different to that 

 Been by the naked eye : 



As this optical problem is solved by means of a glass cut into 

 facets, or what is called a multiplying glass, we (says Hutton, 

 translating Montucla) shall first explain the nature of such 

 glasses. These glasses are generally lenses, plain on one side 

 and cut on the other into several facets in the form of a poly- 

 hedron. Such is the glass shown in front in Fig. 1, and edgewise 

 in Fig. 2. It consists of a plain hexagonal facet in the centre, 



placed perpendicular to the axis continued, and paint on it an 

 image of that facet of a greater or less size, and which, at a 

 certain distance, will be inverted. Consequently, if we suppose 

 the eye to be substituted instead of the luminous point, and 

 that the image itself is luminous or coloured, the rays which 

 proceed from that image or part of the paper will terminate 

 at the eye, and they will be the only ones that reach it after 

 experiencing a double refraction on the same facet. H the like 

 reasoning be employed in regard to the rest, it may be easily 

 seen that when the eye is placed in a fixed point it will 

 observe through each facet only a certain portion of the 

 paper, and that the whole together will fill the field of vision, 

 though detached on the paper ; so that if a certain part of a 

 regular and continued picture be painted on each, they will all 

 together represent the picture. The artifice, then, of the proposed 



and six trapeziums arranged around the circumference. These 

 glasses have the property of representing the object as many 

 times as there are facets, for if we suppose the object to be o, 

 the rays which proceed from it fall upon all the facets of the 

 glass, AD, D c, c B. Those which traverse the facet D c pass 

 through it as through a plain glass interposed between the eye 

 and the object, but the rays which proceed from O to the in- 

 clined facet AD experience a double refraction, which makes 

 them converge towards the axis o E nearly as they would do if 

 they fell on the spherical surface in which the glass polyhedron 

 might be inscribed. The eye being placed in the common point 

 of concurrence, sees the point o at w in the continuation of the 

 radius, E F ; consequently, an image of the point O, different from 

 the former, will be observed. As the same thing takes place in 

 regard to each facet, the object will be seen as many times 

 as there are facets on the glass and in different places. Now, 

 if we suppose a luminous point in the axis of the glass, and at 

 a proper distance, all the rays which fall on one facet will, 

 after a double refraction, proceed to a piece of white paper 



magic picture, after having fixed the place of the eye, that of the 

 glass and the field of the picture, is to determine those portions of 

 the picture which shall alone be seen through the glass ; to paint 

 upon each the determinate portion, according to a given subject, 

 such as a portrait, so that when united together they may pro- 

 duce the painting itself ; and in the last place, to fill up the 

 rest of the field of the picture with anything at pleasure, but 

 arranging the whole in such a manner as to form a regular sub- 

 ject. Having thus explained the principle of this optical amuse- 

 ment, we shall now show how it is to be put in practice. Let 

 A B c D (Fig. 3) represent a board, at the extremity of which is 

 fixed another in a perpendicular direction, having at its edges 

 two pieces of wood, with grooves, to receive a piece of paste- 

 board, covered with white paper or canvas ; this pasteboard, 

 which may be pushed in or drawn out at pleasure, is the field 

 of the intended picture. E G H is a vertical board, the bottom of 

 which may be pushed in or drawn out farther from the picture, 

 and towards the upper part it is furnished with a tube having at 

 its anterior extremity a glass cut into facets, and at the other 





