416 



CHR QMA TICS SPECTRA. 



FIG. 321. 



case of either bow some light is lost at each reflection ; therefore, 

 since there are more reflections in the secondary bow, this will 

 appear fainter. 



646. Chromatic Aberration. It is impossible, 

 by means of a single spherical convex lens, to bring all of 

 the incident rays to a common focus. The blue and violet 



rays being refracted more than 

 the red rays will converge at 

 points nearer the lens. In con- 

 sequence of this, when an image 

 is projected upon a screen, the 

 image is surrounded with a col- 

 ored border, the color depending upon the distance of the 

 screen from the lens. This inability of a single lens 

 to bring differently colored rays to the same focus 

 is called chromatic aberration. 



647. Achromatic Lens. A convex lens of crown 

 glass, by combination with a concave lens of flint glass, may 

 have its dispersive power neutralized without completely 



FIG. 322. 



