352 On the Refraction of Light. 



In looking through the long aperture, placed at a short distance 

 from the eye, dark and bright lines, such as are seen bordering shad- 

 ows and supposed to be deflected from bodies, will appear running 

 parallel to the fissure. Having closed one eye, if we apply the long 

 aperture in such a manner to the other that the pupil shall be nearly 

 covered, and then direct the glance to a luminous object, it will ap- 

 pear beautifully bordered with chromatic light. The uniform devel- 

 opment of color along the edges of bodies, led to some experiments, 

 instituted for the purpose of examining, under various circumstances, 

 this phenomenon. From among them I select the following as being 

 curious and anomalous : close one eye, and with the other look stead- 

 fastly at any luminous object, as the flame of a candle or an illuma- 

 led window ; then move an opaque body (for example the finger,) 

 gradually across the eye ; and when the pupil is nearly covered, the 

 candle flame will appear to glow with the primitive colors. The 

 moon viewed in this manner presents a beautiful and splendid spec- 

 tacle. It is remarkable in this experiment that the colois, supposed 

 to be compound, viz. the orange, green and indigo, are more copi- 

 ously and distinctly developed than the primary ones. Whether the 

 opaque body be black or white, the same unaccountable appearance 

 will be produced. 



When the sun is viewed through a puncture, the transmitted white 

 light is resolved into its elementary hues, and the colors are seen em- 

 anating separa/eZ?/ fron) the sun. 



If we apply the long aperture to the eye, and hold a needle at a short 

 distance behind it, it will form a curve, which beijig gradually bi'ought 

 closer to the eye, will enlarge into the seeming shadow before spo- 

 ken of; but if we place behind the long aperture a broader body, 

 as the flat side of a penknife blade, it will appear cut on either side 

 by a semicircle, thus describing a space between two circles. In 

 passing through a small circular aperture, the image of a candle 

 flame received on a white surface, will be found inverted, Rnd if the 

 white surface be held at some distance, the image will be exceed- 

 ingly magnified, as in the case of its transmission through a double 

 convex lens. In other instances the small aperture displays the prop- 

 erties of a double concave glass, as in giving distinctness and achro- 

 macy to telescopic images. When the image of a candle flame is 

 transmitted through a long incision in the lead, it will be multiplied 

 and present the appearance of a row of lights all inverted. If a 

 plate of lead having many puncturea be held close to a candle flaniCj 



