452 Mr. G. Shaw on some Photographic Phenomena. 



perfect in every part. This production of picture upon pic- 

 tui'e was repeated, until by the confusion of the superposed 

 images the effects of further exposure could be no longer di- 

 stinguished. 



In all the experiments hitherto described the destruction of 

 the impressions by bromine was effected in the dark, the ap- 

 paratus being situated in a room into which only a very feeble 

 daylight was admitted. It remained to be discovered if the 

 mixed vapour had the power of destroying the effect of 

 light while the plate was still exposed to light, or if the 

 vapour had the power of suspending or preventing the ac- 

 tion of light on a Daguerreotype plate. In order to deter- 

 mine this point, the apparatus was placed near the window of 

 a well-lighted room, and so arranged, that during the whole 

 time of the preparation of the plate, by exposure first to iodine 

 and afterwards to bromine, it was exposed to full daylight, 

 and by a mechanical arrangement, of too obvious a nature to 

 render description necessary, the plate was withdrawn from 

 the bromine vessel into a dark box ; that is to say, it was 

 withdrawn at the sa/ne moment from the influence both of light 

 and bromine: on being placed in the camera obscura, plates 

 so prepared received impressions, which by mercurializatlon 

 produced excellent pictures, and there was no trace of the 

 action of any light save that of the camera obscura. It follows 

 then that light is incapable of exerting any appreciable influ- 

 ence on Daguerreotype plates during the time they are re- 

 ceiving their coatings of iodine and bromine. 



Although these experiments afford no information on the 

 subject in reference to which they were originally undertaken, 

 they are yet not without interest, both in their theoretical 

 bearing and in their practical application. They demonstrate 

 not only that the change (whatever it may be) effected by light 

 on silver plates prepared b^ Daguerre's process is completely 

 suspended in the presence of the vapour of either iodine or 

 bromine, but that after that change has been produced the im- 

 pression may be destroyed and the plate restored to its original 

 condition by a momentary exposure to either of these vapours. 

 In their practical application these experiments show, that all 

 the care which has been taken to exclude light from Daguerreo- 

 type plates during their preparation is unnecessary; that so 

 far from a dark room being essential to the operations of the 

 Daguerreotype artist, the light of day may be allowed to fall 

 on the plate during the whole time of its preparation; and 

 that it is only necessary to withdraw it at the same moment from 

 the action of bromine and light by sliding it from the bromine 

 vessel into the dark box in which it is carried to the camera 



