194 



The Philippine Journal of Science 



1913 



photographing the various spectra. Table I shows the limits 

 of the transmitted portion with the various glasses. 



Table I. — Spectra transmitted by various tinted glasses. 



Type of glass. 

 Rontgen 



Clear crown optical 

 Shade No. 1, blue 

 Shade No. 3, blue 

 Shade No. 5, blue 

 Shade No. 2, amber 

 Shade No. 3, amber 

 Shade No. 4, amber 

 Shade No. 6, amber 

 Shade No. 1, London smoke 

 Shade No. 3, London smoke 

 Shade No. 4, London smoke 

 Shade No. 5, London smoke 

 Shade No. 6, London smoke 

 Shade No. 1, amethyst 

 Shade No. 3, amethyst 



Range of transmitted spectra. 

 Wave lengths. 



3,035 to 6,990 

 2,970 to 6,950 

 3,020 to 6,950 

 3,030 to 6,950 

 3,040 to 6,950 

 2,980 to 6,840 

 3,520 to 6,840 

 3,845 to 6,840 

 4,630 to 6,840 

 3,220 to 6,940 

 3,275 to 6,940 

 3,320 to 6,940 

 3,360 to 6,940 

 3,460 to 6,940 

 2,980 to 6,940 

 3,005 to 6,940 



Great accuracy cannot be attained by this means in measur- 

 ing the limits of transmission at the red end of the spectrum. 

 In the case of colorless glass the limit is dependent upon the sen- 

 sitiveness of the plate toward the longer wave lengths. The 

 tinted glasses show decreased intensity of the spectrum in this 

 portion rather than well-marked selective absorption. The fig- 

 ures in the above table defining the red end of the transmitted 

 spectra are included for relative comparisons rather than as 

 definite limits. 



The following table gives the wave lengths corresponding to 

 the middle of the range covered by each of the seven primary 

 colors, and is included for reference. 



Table II. — Wave lengths of the primary colors. 



Color. 



Wave 

 length. 



Red 



Orange _. 



7,000 

 5,972 

 5,808 

 5,271 

 4,732 

 4,383 

 4,059 



Yellow 



Green 



Blue 





Violet 





The Rontgen and clear crown optical glasses transmit the 

 entire visible spectrum unchanged, and only afford protection 



