Research on some Standards of Light. 



479 



Fig. 4. — Apparatus used for the investigation on the Lummer and Kurlbaum incandes- 

 cent platinum standard : — 



1. Incandescent lamp serving as standard of reference. 



2. Lummer and Brodhun photometer head. 



3. Enclosure in which the incandescent platinum foil is placed with the 1 sq. cm. 



diaphragm. 



4. Screen to cut off the radiation from the bolometer. 



5. Water-trough, with quartz sides 2 cm. apart. 



6. Bolometer with the cover removed to show the films. 



7. Bolometer cover. 



8. Clips for holding the incandescent platinum foil ; this plate fits on to the back of 



the enclosure 3. 



9. One of the water circulation diaphragms used to keep any extraneous radiation 



from the bolometer. 



VOL. LXV. 



