274 OPTICAL PROJECTION 



CHAPTEK XVIII 



LIGHT I 

 EEFLECTTON, REFRACTION, DISPERSION, AND COLOUR 



THE phenomena of Light not only lend themselves most 

 readily of all to demonstration by the lantern, but in studying 

 them we best acquire a mastery of the various manipulations 

 of beams and pencils of light required in the demonstration of 

 other subjects. For this reason, the demonstrator in other 

 departments, though he may not himself desire to perform 

 purely optical experiments, will do well to read and understand 

 what is said respecting their details and methods, for the 

 sake of the hints which these may give him in handling his 

 tools. 



151. Kays of Light. The image-forming power of rays of 

 light, the inversion of images, and the relation of the size of 

 the image to the distance from the aperture or lens by which 

 it is formed, cannot be better shown than by the experiments 

 described in Chapter I., pp. 2, 3. 



That rays are really reflected from ordinary bodies may be 

 easily shown by removing everything from the nozzle of the 

 lantern, and receiving the full parallel beam, or still better a 

 slightly divergent beam, at an angle of about 45, on a large 

 piece of card, on which is pasted red surf ace -paper with a 

 * dead ' surface. On holding another white card as a screen 

 some little way off, it will be seen that a strong red light is 

 thrown upon this by the reflected rays ; and other colours 

 will display similar effects. The colours should be as rich 

 and ' full-bodied ' as possible but a glossy surface should be 

 avoided, that it may be clear the effect is produced solely by 

 scattered reflection. 



152. Scattered Reflection. That we only see things, not 



