OP AETS AND SCIENCES. 171 



VIII. 



ON THE PHOTOGRAPHIC ACTION OF DRY SILVER BRO- 

 MIDE COLLODION, &c., TO RAYS OF SOLAR LIGHT OF 

 DIFFERENT REFRANGIBILITY. 



By Robert Amory, M.D., Longwood. 



Presented June 10th, 1877. 



1. In continuation of experiments reported to the Academy in May, 

 1876, 1 present the following results : Further experiments demonstrate 

 that silver bromide collodion is sensitive to all the visible rays of the 

 spectrum, but requires a very prolonged exposure to the less refrangible 

 rays. A gradual decrease of photographic action in reducing the silver 

 salt is observed from about line F to line A, the latter being almost 

 imperceptible, though by careful observation a very thin deposit of 

 metallic silver can be made out at the red end. 



2. Some of the glucosides, such as salicin, amygdalin, populin, and 

 santonin, slightly increase the photographic action of the silver salt, 

 when exposed to the less refrangible rays. This reduction of the silver 

 salt does not occur as a selective action, — that is to say, in certain isolated 

 portions of the spectrum ; but the photographic image is somewhat 

 stronger at F, and gradually fades out towards line A. 



3. Stewart- Wortley dry plates, which contain salicin and ui-aniura 

 with the silver bromide, on exposure to the solar spectrum, show an 

 increased action from F to A, and the image is stronger than when a 

 glucoside alone is added to the silver bromide ; but in these there is no 

 selective action below line F. 



4. Colonel Abney claims that the addition of benzoin and bromine 

 to a collodion made at a high temperature increases the sensitiveness 

 of a silver bromide dry plate to the less refrangible rays of the spec- 

 trum, and to some of the ultra red rays. Only one plate out of a large 

 number prepared according to Colonel Abney's directions * bears in my 

 hands any confirmation of his results. It should, however, be observed 

 that the presence of benzoin and bromine in a sensitized collodion plate, 



* The details of the process were kindly sent by him to me. 



