The Dispersion and Absorption of Fuchsin 



17 



fleeting prisms p and p' by means of a split lens 5. Then prisms 

 reflect the light on to the mirrors in and ni , and these direct the 

 light on to the collimator slits. Part of the light from 

 the right-hand collimator reaches the observing telescope by 



If 



reflection from a silvered strip cemented in the comparison 

 prism P. The rest passes above or below the strip and 

 is lost. On the other hand, of the light which comes from 



117 



