ON LIGHT. 325 



gined more singular and bizarre than the appearance of 

 shadows cast on a screen in this manner by a variety of 

 minute objects of different shapes, needles, feathers, 

 lace-work, locks of hair, &c. ; and as their observation, 

 as we have shown, is exceedingly simple and easy, we 

 earnestly recommend them to the attention of our 

 readers a bit of looking-glass, or, still better, a polished 

 metallic reflector, a hole in a window shutter, a lens of 

 an inch focus, a screen of white paper, and a sunny day, 

 being all the requisites. 



(108.) When the image of a small circular aperture (as 

 a pin hole) is thrown on the screen, it is seen as a small 

 round disc, highly coloured, the colours varying as the 

 screen is approached from a distance to the hole pre- 

 senting in regular succession the tints of the reflected 

 colours of thin plates described in a former part of this 

 article, beginning with the first white : or, if the illumin- 

 ation be effected by homogenous light, alternate grada- 

 tions of light from brightness down to total obscurity, 

 and thence through an alternate succession of light and 

 darkness. Around the central spot, too, coloured rings 

 are formed, the tints of which vary in dependence on 

 those of the centre. When the light is transmitted 

 through two holes side by side, and very near together, 

 besides the rings belonging to each, a set of intersectional 

 coloured streaks is formed, straight if the holes be equal, 

 hyperbolically curved if unequal. With three holes form- 

 ing an equilateral triangle, or with a still greater number 

 arranged with perfect regularity (as in machine-stamped 

 paper in patterns), an endless variety of elegant and 



