XI 



LIGHT 



170 



Recomposition of White Light. If in Expt. 173, after 

 having decomposed sunlight to form a spectrum, we place a 



FIG. 92. Recomposition of Light by a Second Prism. 



second similar prism after the first with its refracting angle 

 reversed, it will be seen that the spectrum disappears, and in its 



FIG. 93. The Colour Disc. 



place we get a white image of the slit, not opposite the slit, but 

 displaced owing to the refraction produced by the prisms. But 



N 2 



