SCIOPTICON MANUAL. 13 



EXPERIMENTAL VERIFICATION. 



These properties of the camera obscura, thus far con- 

 sidered, may receive more lively illustrations by actually 

 darkening a room and admitting light through, say an 

 inch hole. A room with but one window, and that 

 looking from the sun, and towards objects illuminated 

 by sunlight, is to be preferred. A lens, if one is used, 

 of long focal distance (nearly flat) gives more room for 

 spectators before the screen. The images, if the lens 

 has short focus, may be better seen on the back of a 

 semi-transparent screen by transmitted light, as they 

 are seen on the ground-glass in a photographic camera. 

 These moving pictures of busy life and wavy trees, of 

 curling smoke and floating clouds, are peculiarly 

 pleasing and beautiful, as well as suggestive of im- 

 portant principles in optics. 



INDISTINCTNESS. 



Fig. 1 fails of showing the divergence of each pencil 

 of light to the size of the aperture as seen at c (Fig. 3) ; 



Fig. 8. 



a property which renders the image indistinct, from the 

 consequent overlapping of the blunt ends, so to speak, 

 of innumerable pencils. 



CONVEX EENS. 



In accordance with the law of refraction, rays as 

 from d (Fig. 4) are bent towards a perpendicular in 

 entering the convex lens /, and from a perpendicular in 



