EXPERIMENTS 269 



ing, by having blindfolded subject point in direction of sounds 

 heard. Close one ear and repeat. 



[7) Demonstrate graphically the varying characteristics of 

 sound waves by projecting tones of voice and cornet into speak- 

 ing tube of apparatus, at same time that revolving mirror is 

 whirled to separate the tongues of flame produced by sound 

 waves.] 



Vision 



Materials: Color top with color disks; set of worsteds for 

 testing color blindness; small glass prism, 60 angles; camera 

 with ground glass, or ordinary magnifying glass with cardboard 

 diaphragms having central openings of *4, ^ and 1 in.; 

 spectacle lenses, concave and convex of varying strengths; 

 candle ; screen, a piece of cardboard placed in a vertical position 

 on a base; [sharp scalpel; curved scissors; forceps]. 



1) Demonstrate formation of image by lens. Use camera 

 with ground glass, or ordinary magnifying glass, and receive 

 image on paper. Note a) Relative sizes of images of near and 

 far objects, b) Relative lengths of focus for near and far 

 objects. 



2) Test effect of different-sized diaphragms on brightness- 

 and sharpness of images. 



3) Analyze white light (sunlight) by means of prism throw- 

 ing spectrum on white paper. 



4) Mix colors by means of color top : 



a) Black with white in different proportions (grays). 



b) Various colors with white (tints). 



c) " " " black (shades). 



d) " " " each other. 



5) Color blindness: Give to pupil a set of standard colors 

 and their tints and shades. Hold up in succession different 

 colors and ask for selection of all pieces resembling them. 



6) Near-sight: Place candle on table; two feet distant, set 

 screen. Place magnifying glass between, so as to throw focus 

 on screen. Move screen away from lens until image is blurred, 

 to imitate the elongated eye of near-sight. Take small piece of 

 paper and locate focus by moving it between lens and screea 

 until image on it is distinct. 



