200 



TABLE 216. 

 TRANSMISSIBILITY FOR RADIATION. 



Transmissibility of the Various Substances of Tables 166 to 175. 



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



Metallic reflection at 9.05/1 and 30 to 40^. 



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

 a i cm. thick plate in % : 



i iiutiwi i A. UTO* ^* 3* y^^r I o o 



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

 Metallic reflection at 0.110/1, 0.156, 51.2, and 87/*. 

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



Metallic reflection at 0.1141*, 0.161, 61.1, 100. 

 Fluorite : Very transparent for the ultra-violet nearly to O.I/A. 

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



Metallic reflection at 24/4, 31.6, 40/1. 



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

 i = i e- kd (d in cm.) : 

 For the ordinary ray : 



For the extraordinary ray : 



Quartz : Very transparent to the ultra-violet ; Pfliiger gets the following transmission values for 



a plate i cm. thick: at 0.222/4, 94.2%; 0.214, 92 ; 0.203, 8 3-6 ; 0.186, 67.2%. 



Merritt (Wied. Ann. 55, 1895) gi ves the following values for k (see formula under Iceland Spar) : 

 For the ordinary ray : 



For the extraordinary ray : 



For A>7 /^becomes opaque, metallic reflection at 8.50/1, 9.02, 20.75-244/4, then trans- 

 parent again. 



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

 SMITHSONIAN TABLES. 



