202 THE ROYAL SOCIETY OF CANADA 



Figs. 15-19 represent the photographs made with the first five 

 filters in the way explained above. An attempt was made to make 

 corresponding photographs with the asphaltum filter but no notice- 

 able result was obtained. Fig. 15 shows that filter No. 22 begins to 

 transmit in the neighbourhood of X 4900A and consequently can be 

 used with gratings for work between X 4900A and X 9,800A. Fig. 16 

 shows that filters No. 29 and No. 22 combined are good for work 

 between X 6,100A and X 12,200A. Fig. 17 shows that the combination 

 of No. 70 and No. 22 can be used for the region from X 6,400A up to 

 X 12,800A. Fig. 18 shows that filters No. 36 and No. 29 begin to 

 transmit at X 6,700A and consequently can be used for work between 

 X 6700A and X 13,400A. Fig. 19, filters No. 29 and No. 45 (Paschen), 

 shows that this filter transmits from X 6,900A, and can be used for 

 work from X 7000A and up to X 14,O00A, although it is transparent 

 for a narrow region between X 3342A and X 3655A. 



Fig. 14 shows asphaltum can furnish a cheap and highly trans- 

 parent filter for infra-red work. 



(5) Summary of Results 



1. Six different dyes were studied and it was found that they all 

 absorb only to a very small extent rediations of wave-lengths longer 

 than X 9000A, which fact accounts for the long exposure required for 

 successful photography in this spectral region. 



2. The results obtained indicate that the use of proper mixtures 

 of the dyes may prove helpful in photographing beyond X 9000A. 



3. Observations on absorption indicate that, although not so 

 popular, Nigrosin and Alizarin Blue may be of greater use for certain 

 regions of the spectrum than Dicaynin or Dicyanin A. 



4. According to the absorption curves photography, as far up as 

 X 20000A ,should not be more difficult than to X lOOOOA. 



5. Six useful filters were investigated in two ways, i.e., as to 

 transparency, and as to the region in which they can be most efficiently 

 used. 



Part II. On Infra-Red Photography 



In a paper published by McLennan and Shaver,^ it was shown 

 that the mercury spectrum can be photographed as far as X 11, 137 A. 

 Photographs of the type produced in their paper were made by means 

 of a grating spectrograph, and required exposures ranging from 17 

 to 32 hours. Wishing to investigate the influence of different ex- 

 posures on the stained plates and on the other hand, desiring to 



iMcLennan and Shaver, Proc. Roy. Soc. A, 100, p. 200, 1921. 



