200 



Table 216. 

 TRANSMISSIBILITY FOR RADIATION. 



Transmlssllilllty of the Various Substances ol Tables 166 to 175. 



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



Metallic reflection at g.oSju and 30 to 40^. 

 Rock-salt : Rubens and Trowbridge (Wied. Ann. 65, 189S) give the following transparencies for 

 a I cm. thick plate in % : 



23-7M 



% 



99-5 



99-5 



99-3 



13 



14 



97-6 93-1 



84.6 



16 



17 



66.1 



51.6 



18 



27-5 



19 



9.6 



20.7 



0.6 



Pflii<Ter (Phys. Zt. 5. 1904) gives the following for the ultra-violet, same thickness : 280/^^, 95-5% ; 



23''i,86%; 210,77%; i86r7o%. 

 Metallic reflection at o.iiOfj., 0.156, 51.2, and 87/i. 

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



Metallic reflection at 0.114^. o.i6r, 61. i, 100. 

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



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



Metallic reflection at 24^^, 31.6, 40 (jl. 

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

 i = ioC"" (d in cm.) : 

 For the ordinary ray 



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

 a plate i cm. thick: at 0.2221J.. 94.2%; 0.214, 92 ; 0.203, 83.6; 0.186, 67.2%. 

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

 For the ordinary ray : 



For \>7 ;it, becomes opaque, metallic reflection at 8.50^4, 9.02, 20.7 5-24.4;u, then trans- 

 parent again. 



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

 SwrTHSONiAN Tables. 



