196 



TABLE 1 92. 

 TRANSMISSIBILITY FOR RADIATION, 



Color Screens. Jena Glasses. 



See " Uber Farbgl'aser fur wissenschaftliche und technische Zwecke," by Zsigmondy, Z. fur In- 

 strumentenkunde, 21, 1901 (from which the above table is taken), and " Cber Jenenser Licht- 

 filter," by Grebe, same volume. 

 (The following notes are quoted from Everett's translation of the above in the English edition of 



Hovestadt's " Jena Glass.") 

 Division of the spectrum into complementary colors : 



1st by 2728 (deep red) and 2742 (blue, like copper sulphate). 

 2nd by 454 (bright yellow) and 447'" (blue, like cobalt glass). 

 3rd by 433 (greenish-yellow) and 424 m (blue). 

 Thicknesses necessary in above : 2728, 1.6-1.7 mm. ; 2742,5; 4S4 ra , 16; 447, 1.5-2.0; 433, 



2.5-3.5; 424 m , 3mm. 



Three-fold division into red, green and blue (with violet) : 

 2728, 1.7 mm. ; 4i4 m , 10 mm.; 447 111 , 1.5 mm., or by 

 2728, 1.7 mm. ; 436 111 , 2.6mm. ; 447, 1.8 mm. 



Grebe found the three following glasses specially suited for the additive methods of three-color 

 projection : 



2745, red; 438 m , green; 447 m , blue violet; 



corresponding closely to Young's three elementary color sensations. 

 Most of the Jena glasses can be supplied to order, but the absorption bands vary somewhat in 



different meltings. 



See also " Atlas of Absorption Spectra," Uhler and Wood, Carnegie Institution Publications, 

 1907. 



SMITHSONIAN TABLES. 



