[young-ireton] 



OPTICAL TRANSPARENCY 

 Table I 



17 



The samples of fluorite described in this paper were supplied by 

 the Adam Hilger Co., and the investigation was carried out in the 

 Admiralty Physical Laboratory, South Kensington. 



The illustration Plate I shows spectra of the carbon arc radiation 

 transmitted by various types of fluorite (a) transmission to 1900 A.U., 

 (b) to 1656 A.U., (c) to 1550 A.U., (d) to 1464 A.U., (e) the carbon arc 

 through the optical train of the spectrograph only. 



Summary 



It will be seen from the above table that many of the samples 

 compare favourably with the fluorite supplied by Zeiss for spectro- 



