r.'.u; 



sr.M.MAUV OF CUKRKNT RKSKARCHES RELATING TO 



high dispersion. One of these discs carries a totally reflecting prism, 

 through which light passes from the comparison light-source; it also 

 carries a holder, in which gauged smoke-glass wedges with scale and 



QO 



6 



platinized glass plates can be inserted for weakening the light-source to 

 a measurable quantity. A second disc is provided for photometric com- 

 parisons with the smoke-glass wedges in the direction of the collimator- 

 tube : this arrangement is for measuring the selective absorption of 



