194 Table 189. 



TRANSMISSIBILITY FOR RADIATION. 



TransmlsslblUty o2 the Vartons Snbstanoes ol Tal)les 166 to 176. 



Alum : Ordinary alum (crystal) absorbs the infra-red. 



Metallic reflection at 9.05/* and 30 to 40/x, 

 Rock-salt : Rubens and Trowbridge (Wied. Ann. 65, 1898) give the following transparencies foi 

 a I cm. thick plate in % : 



Pfluger (Phys. Zt. 5. 1904) gives the following for the ultra-violet, same thickness : 2%oixn, 95.5% 



231,86%; 210,77%; 186,70%. 

 Metallic reflection at o.iiOjtt, 0.156, 51.2, and 87^. 

 Sylvine : Transparency of a i cm. thick plate (Trowbridge, Wied. Ann. 60, 1897). 



Metallic reflection at 0.114/*, 0.161, 61. i, 100. 

 Fluorite : Very transparent for the ultra-violet nearly to o.i/t. 

 Rubens and Trowbridge give the following for a i cm. plate (Wied. Ann. 60, 1897) : 



Metallic reflection at 24/u, 31.6, 40/*. 

 Iceland Spar: Merritt (Wied. Ann. 55, 1895) gives the following values of k in the formula 

 i = ioe-'* (d in cm.) : 

 For the ordinary ray : 



Quartz : Very transparent to the ultra-violet ; Pfluger gets the following transmission values fori 

 a plate i cm. thick: at 0.222/*, 94.2%; 0.214, 92 ; 0.203, 83.6; 0.186, 67.2%. 

 Merritt (Wied. Ann. 55, 1895) gives the following values for k (see formula under Iceland Spar) ; 

 For the ordinary ray : 



For X>7 /*, becomes opaque, metallic reflection at 8.50/1, 9.02, 20.75-24.4/*, then trans- 

 parent again. 



The above are taken from Kayser's " Handbuch der Spectroscopic," vol. iii. 

 Smithsonian Tablcs. 



