TABLE 565.— TRANSPARENCY OF VARIOUS SUBSTANCES 545 



Alum: Ordinary alum (crystal) absorbs the infrared. 

 Metallic reflection at 9.05m and 30 to 40m. 



Rock salt: Rubens and Trowbridge give the following transparencies for a 1 cm thick 

 plate in percent : 



Pfliiger gives the following for the ultraviolet, same thickness: 280mm. 95.5 percent; 231. 



86 percent; 210, 77 percent; 186, 70 percent. 

 Metallic reflection at 0.110m, 0.156, 51.2, and 87m. 



Sylvite : Transparency of a 1 cm thick plate : 



X 9 10 11 12 13 14 15 



% 100. 98.8 99.0 99.5 99.5 97.5 95.4 



Metallic reflection at 0.114m, 0.161, 61.1, 100. 



Fluorite: Very transparent for the ultraviolet nearly to 0.1m. 

 Rubens and Trowbridge give the following for a 1 cm plate : 



X 8m 9 10 11 12m 



% 84.4 54.3 16.4 1.0 



Metallic reflection at 24m, 31.6, 40m- 



Iceland spar: Merritt gives the following values of k in the formula i = ioe~* d (d in cm) : 

 For the ordinary ray : 



X 1.02 1.45 1.72 2.07 2.11 2.30 2.44 2.53 2.60 2.65 2.74m 



k .0 .0 .03 .13 .74 1.92 3.00 1.92 1.21 1.74 2.36 

 X 2.83 2.90 2.95 3.04 3.30 3.47 3.62 3.80 3.98 4.35 4.52 4.83m 



k 1.32 .70 1.80 4.71 22.7 19.4 9.6 18.6 °° 6.6 14.3 6.1 

 For the extraordinary ray : 



X 2.49 2.87 3.00 3.28 3.38 3.59 3.76 3.90 4.02 4.41 4.67m 



k .14 .08 .43 1.32 .89 1.79 2.04 1.17 .89 1.07 2.40 

 X 4.91 5.04 5.34 5.50m 

 k 1.25 2.13 4.41 12.8 



Quartz: Very transparent to the ultraviolet; Pfliiger gets the . following transmission 

 values for a plate 1 cm thick: at 0.222m, 94.2 percent; 0.214, 92; 0.203, 83.6; 0.186, 67.2 

 percent. 

 Merritt gives the following values for k (see formula under Iceland spar) : 

 For the ordinary ray : 



X 2.72 2.83 2.95 3.07 



k .20 .47 .57 .31 



For the extraordinary ray : 



X 2.74 2.89 3.00 3.08 3.26 



k .0 .11 .33 .26 .11 



For \>7 n, becomes opaque, metallic reflection at 8.50m, 9.02, 20.75-24.4m, then trans- 

 parent again. 



TABLE 566.— TRANSPARENCY OF WATER VAPOR (steam) 



SMITHSONIAN PHYSICAL TABLES 



