900 Infra-Red Investigations with the Echelette Grating. 



The wave-lengths of the maxima of the bands for the 

 quartz rays and the radiations from the flame have been very 



Fisr. 2. 



carefully determined. The single between the collimating 

 mirrors of the vacuum spectrometer were determined, and 

 the formula for fixed collimator and telescope and revolving 

 grating. In the case of the quartz rays the following values 

 were obtained : — 



8-42 



8-90 



8-42 



8-99 



8-40 



8-80 



8-36 



890 



8-49 



8-90 



Mean ... 8'41/a 



8'90/z 



For the flame radiations the following values were found 

 for the three maxima, 4'2/z, 4*4/x, 4*5/x (these values were 

 obtained from calculations made both from the second and 

 third order spectra of grating No. 6). With grating No. 5 

 the values of the two brightest maxima were 4' 32//, and 

 4-43^. 



