1895.] 



Phosphorescence and Photographic Action. 



669 



nary temperature. The first plan (Fig. 2) was simply to immerse a 

 strip of sensitive bromide paper A B, in one of the vacuum vessels 

 containing liquid oxygen, and when the part immersed had been 

 thoroughly cooled down, exposing it to the light of a piece of burning 

 magnesium. The paper was then developed, when a result some- 

 thing resembling was obtained. The part which had been cooled 

 by the liquid oxygen, as at A, was untouched by the light, whereas 

 the portion of paper above the liquid at B developed up quite black. 

 Further modifications were made in Fig. 3, where the strip of sensi- 

 tive film E was enclosed in a cover of sheet lead B, having two small 

 discs cut away as at C and D. The strip was then cooled in liquid 



n 



D 



Fig. 4. 



oxygen A, and then exposed to a flash of burning magnesium. After 

 development, the strip appeared something like E, when again the 

 action of the light was considerably diminished on the part of the 

 film which had been cooled. In Fig. 4 a form of apparatus was 

 adopted whereby the exposures were made without the disadvantage 

 of the light passing through the glass sides of the vacuum vessels. 

 B and E were vacuum vessels enclosed in a blackened box; into B 

 a quantity of liquid oxygen was poured. The sensitive plate or film 

 was then lowered so as just to touch the surface of the liquid as at 

 C. D was a comparison plate exposed at the same time and at the 

 same distance from the source of light A, only the comparison plate 



