494 



Major-Geiieral J. Waterliouse. The Sensitiveness 



washed with benzene to remove all greasiness. After half an hour's 

 exposure in dull sunlight and development with merciu-y, an image was 

 produced similar to the two first on silver leaf, i.e., the mercury had 

 deposited upon the exposed parts. 



These experiments \nth. three different forms of silver surfaces and 

 two methods of development, all giving results similar to those 

 obtained by Moser, seemed at any rate to prove the correctness of his 

 observation, and the sensitiveness of ordinary forms of silver to 

 light. 



With the exception of the first, the foregoing trials were all made 

 with a black and white negative on glass. Others were then made 

 with cut-out black paper screens and with like results. 



Ohservation of Printecl-out Visible Image. — The first observation of an 

 image visible on the silver surface after exposure and without any 

 development was on a plate of nearly pure silver, cleaned \n.th. tripoli 

 and ammonia, polished off with dry tripoli, and exposed on the 21st 

 August for about half an hoiu" in sunshine under a black paper cut-out 

 >screen. The parts exposed to light appeared lighter than the unex- 

 posed, but on development the mercury was deposited upon the unex- 

 posed parts. In this case, the surface may have been affected by the 

 ammonia used in cleaning, but it is also likely that the black paper 

 used for the mask exercised some effect, as was afterwards found to be 

 the case. 



Another silver plate exposed for the same time imder the same cut- 

 out mask, but separated from it by a sheet of mica, did not show the 

 visible image after exposiu-e, though an image was readily developed 

 with mercury vapoiu*. 



A day or two later, on the 24th August, the same experiment was 

 repeated upon a plate of silvered glass exposed in the sun for half an 

 hour under the cut-out mask, with a mica screen between it and the 

 silvered surface. The image of the black paper design could be 

 faintly but distinctly discerned in a suitable light, again appearing 

 dark upon a lighter groimd. Development with acid iron and silver 

 brought out clearly the images of the paper mask, and of some letters 

 cut out of the mica screen, as well as the edges of the mica screen 

 itself. 



A piece of silvered glass was then exposed for forty-five minutes 

 under the same black and white negative as used in the first experi- 

 ments, the silvered surface being protected from contact with the 

 negative by a mica screen. In this case also a faint image was visible 

 after exposure. 



Several other prints, both from the lace negative and the paper 

 masks, were made on silvered glass with longer exposures, so as to 

 obtain a distinctly visible image, and it was then found that there was 

 a tendency to reversal of the image when developed with mercury 



