CHR OMA TICS SPECTRA. 409 



ECTfON IV. 



CHROMATICS. SPECTRA. 



634. Other Results of Refraction. In our previous 

 consideration of luminous rays we have studied the effect of reflec- 

 tion and refraction upon the direction of rays ; in fact, we have 

 dealt with only those properties which are common to all luminous 

 rays. But the properties of light and the phenomena of refraction 

 are not so simple as we might thus be led to suppose. Most 

 luminous objects emit light of several kinds blended together. We 

 must not be satisfied with our knowledge of light until we are able 

 to sift these varieties one from the other, and to deal with any one 

 kind by itself. 



FIG. 314. 



635. Solar Spectrum. Admit a sunbeam through 

 a very small opening in the shutter of a darkened room. 

 The opening may be prepared by cutting a slit an inch 

 (25 mm.) long and ^g- of an inch (1 mm.) wide in a card. 

 See that the edges of the slit are smooth. Tack the slit 

 over a larger opening in the shutter. If we look at the 

 aperture from E we shall see the sun beyond. The path 

 of the beam from S to E is made visible by the floating 

 18 



