OP ARTS AND SCIENCES. 301 



XX. 



CONTRIBUTIONS FROM THE JEFFERSON PHYSICAL 

 LABORATORY. 



PHOTOGRAPHY OF THE LEAST REFRANGIBLE 

 PORTION OF THE SOLAR SPECTRUM. 



By J. C. B. Burbank. 



Presented by Professor Trowbridge, March 14, 1888. 



It has been stated by eminent authorities, that the process of staining 

 dry plates with various dyes is not applicable to the photography of 

 the invisible rays beyond the red of the solar spectrum. To test this 

 question I have undertaken a series of experiments with the dye 

 cyanine. This dye has of late come into considerable prominence 

 in photography, owing to its orthochromatic effect when mixed with 

 other dyes, such as chinoline-red, azaline, erythrosine, and eosine. 



It was discovered by Greville Williams, an Englishman, in 1861, 

 but did not come into much prominence until the year 1884, when its 

 usefulness as a sensitizer became more apparent. The dye is easily 

 decomposed by light, and even in the dark both its solution and the 

 plates coated with it are apt to become decomposed if kept for any 

 length of time. Alone, it has been found very useful to sensitize 

 plates for the orange and red portions of the spectrum. No experi- 

 ments have to my knowledge been made upon the effect of heat rays 

 upon cyanine plates. 



The direct action of absorbents in the infra red has not, hitherto, 

 been tried with any success ; moreover, it has been stated by so emi- 

 nent an authority as Captain W. De W. Abney that it was impossible 

 to make plates sensitive to any rays below the A of the solar spectrum 

 by means of the addition of dyes to a film. It is true, however, that 

 Major Waterhouse has succeeded by means of turmeric in obtaining 

 evidence of the existence of a few lines on the less refrangible side 

 of A, but in all cases except one these were reversed. 



The plates employed were made by the M. A. Seed Co. of sensi- 

 tometer 22. The method used in staining the plates and in the prepa- 



