1890.] NEW YORK ACADEMY OF SCIENCES. 103 



the plain plate ; but with the same exposure of several minutes, 

 only the blue line of the strontium spectrum distinctly affected 

 either plate, and that appeared to affect both about equally. 

 Pure hydrogen gas, giving no spectrum of its own, was the 

 flame employed. 



The subject of reversal of the image was next discussed, and 

 illustrated by several examples occurring in the case of fire- 

 works, Geissler tubes, and direct views of the setting sun. 

 From these it was concluded that important revelations might 

 result from photographing objects illuminated successively by 

 monochromatic lights of various wave-lengths ; as an antago- 

 nistic or complementary action between the more and the less 

 refrangible rays, most pronounced between the blue and red, 

 seems to be concerned in reversals. 



The utility of the photography of self-luminous subjects was 

 next considered ; and in illustration of its application for pre- 

 serving historical mementoes, there were presented, — 6rst, a 

 view of the burning Brooklyn Tabernacle at night, and next a 

 view, by M. Albert Londe, of the illumination of the Trocadero 

 in Paris at the opening of the Exposition. 



But its utility was considered as more apparent in the pro- 

 duction of combination exposures. These were exemplified by 

 an interior daylight view of the electric exhibition in Philadel- 

 phia, decorated with electric lamps, taken on September 27th, 

 1884, and a daylight view of a zinc-furnace in operation, show- 

 ing the flames of the burning zinc escaping from the mouths 

 of the retorts. Another variety of combination exposures was 

 typified by a portrait of a smoker lighting his pipe near a 

 lighted lamp, — the lamp and match flames being taken by 

 direct exposure, the portrait by flash-light. 



Finally, a picture of a watch-spring burning in oxygen, ob- 

 tained by the same method, was shown as perhaps the first of 

 its kind and likely to be followed by views of other experiments, 

 as of antimony and arsenic burning in chlorine ; and it was 

 suggested that photo-engravings of such pictures should soon 

 replace the woodcuts now used in text-books. 



The paper was illustrated by about seventy-five original and 

 highly novel lantern views, many of which, by Dr. Levison, 

 were shown for the first time. 



Prof. Albert R. Leeds made remarks upon the paper, ex- 

 pressing his great pleasure and interest in the beautiful results 

 presented, and his appreciation of the scientific and persever- 

 ing character of Dr. Levison's work. 



Similar remarks were made by the Chair. 



