54 Dr.E.H.Cook on Experiments 



As the thickness of the wrapping increased, definition on 

 the developed plate became less and less. Thinking the effect 

 might be due to the fact that the brown paper wrapping was 

 not light-tight experiments were made to test this idea, and 

 it should here be mentioned that the brown paper referred to 

 is that which is used, by photographic-plate makers to wrap 

 sensitive plates in. Firstly, a plate wrapped in one fold was 

 exposed for one hour to the light of an ordinary 8 c. p. glow- 

 lamp illuminated by a 105 volt alternating current. A negative 

 was obtained clearly showing images of the objects placed on 

 the brown paper. This seemed to support the idea. Then 

 a wrapped-up plate was simply exposed to diffused daylight 

 for two hours. A very faint and blurred image of the coins 

 &c. was obtained. Thus showing that the paper was not 

 absolutely light-tight. Moreover, by exposing to very power- 

 ful light, such as that from burning magnesium and the 

 lime-light, clearer effects were obtained, showing that the 

 more powerful light is capable of getting through the paper 

 better. 



8. Reproduction of Prints fyc. by Brush-Discharge. 



Whilst engaged in obtaining a perfectly light-tight 

 wrapping for the plates it happened that a piece of ordinary 

 notepaper was used and the whole exposed to the action of 

 the brush. On developing the plate a clearly-defined image of 

 the watermark of the paper was produced (fig. 4) . This induced 

 trying to copy in a similar way printing, writing, pictures, 

 &c. In every case this has been done with complete success. 

 If a photograph, or a drawing, or printing, or writing be placed 

 in contact with the sensitive film and exposed to the brush- 

 discharge, a clearly-defined and very sharp reproduction is 

 obtained. This seems to be more readily produced by the 

 positive brush than by the negative. The effect on the plate 

 can also be produced if the drawing be not in contact with 

 the film but separated from it by one or two layers of paper 

 or cardboard. In the latter case, however, the definition is 

 not so good. 



The effects produced when the drawings are in contact 

 cannot be produced simply by keeping the plate and print in 

 contact, at any rate for the same time as was used in my 

 experiments, but can be brought about by exposing the plate 

 to a powerful light, providing the wrappings are not too 

 many. 



One of the results of these experiments, of a somewhat 

 startling character perhaps, is that the writing on a letter 

 inside an envelope can be reproduced. It may be some 



