SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 107, NO. 19, PL. 1 



General View of the Radiometer Set-up within the Constant- 

 temperature ROOM OF THE 100-inch TELESCOPE 



At a the brilliant Mazda lamp, with tube ending at b with pinhole diaphragms 

 at either end of the tube. At c a mirror to reflect spectra directly downward 

 through the quartz lens at d into the radiometer case at c. Opposite / are mirrors 

 to reflect the reading beam 5 meters to the scale and reading device /;. At <j is the 

 micrometer to set and read spectrum positions. Opposite to i is the cord for 

 moving the spectra from one radiometer vane to the other. 



