274 



BULLETIN OP THE UNIVERSITY OF WISCONSIN. 



Table VII — Continued. 

 Prism No. 11. Angle 32". 7. 



Prism No. 15. Angle 2' 10M. 



733.0 

 683.0 

 672.0 

 657.0 



(b) Investigations in the Ultra Violet. — The dispersion hav- 

 ing been measured visually with the spectrometer as far into 

 the violet region as was possible, the photographic method em- 

 ployed by Pniiger 1 was adopted to extend the work into the 

 ultra violet. The arrangement of the apparatus is seen in fig- 

 ure 5 except that sunlight was used instead of the light from 

 the iron arc. 



A solar spectrum thrown by a Rowland concave grating was 

 received upon a photographic plate. Between the grating, E, 

 Fig. 5, and the plate, F, was placed an opaque screen, H, pro- 

 vided with a rectangular aperture over which was fastened the 

 glass plate supporting the cyanin prism. A strip of black pa- 



^Pfluger, Wled. Ann. LXV., p. 206. 



