1887.] Li. -C ol. Waterhouse exhibited photographs. 95 



In order to produce this sensitiveness to yellow the photographic film 

 of bromide of silver is stained with certain dyes, which increase the 

 Sensitiveness of the film for the less refrangible rays of the spectrum. 

 Among them chlorophyll, cyanin blue, eosin and its derivatives, especially 

 those with a bluish tint, such as erythrosin, an alkaline salt of tetraiod- 

 fluorescein. 



At the meeting of the Society in January 1876 I read a short paper, 

 published in the Proceedings, on the influence of Eosin on the photogra- 

 phic action of the Solar Spectrum upon bromide and bromoiodido 

 of silver, and showed its peculiar action in extending the sensitiveness 

 of the bromide of silver to the yellow rays and, in fact, changing the 

 maximum of photographic action from the indigo and violet, as in ordinary 

 plates, to the green and yellow. As stated at the time, my efforts to 

 apply this principle to copying coloured maps, yellow manuscripts, land- 

 scapes &c, on wet and dry collodion plates were not successful and I had 

 not leisure to pursue the enquiry further. Others, however, I am glad to 

 say, have been more successful. Ducos du Hauron found that in order to 

 get the full benefit of the dye on collodion plates it was necessary to ex- 

 pose the plate through a coloured medium such as yellow glass, and by this 

 means he worked very successfully with eosin. Abney, Vogel and Amory 

 also experimented with the dye, and the latter, discovered an import- 

 ant property it has of forming an insoluble compound with nitrate 

 of silver. However, no very practical steps seem to have been taken 

 to utilise this dye for gelatine dry plates till Messrs. Attout, Tail- 

 lefer and Clayton took out a patent for orthochromatic plates early in 

 1883, their plates being prepared either with eosin and ammonia, added 

 to the gelatino-bromide of silver emulsion at the time of making, or by 

 bathing the gelatine dry plates in a bath of eosin, ammonia and alcohol. 

 Since then other modifications of the same principle have been adopted. 

 Plates have also been prepared by Dr. H. W. Vogel, whose original re- 

 searches in this direction have really been the foundation of orthochro- 

 matic photography, with a violet dye, called azalin, which is said to be a 

 mixture of chinolin red and cyanine blue. 



The illuminations and fireworks on the occasion of the Jubilee seemed 

 to offer a good opportunity of testing the sensitiveness of these orthochro- 

 matic plates to the yellow light given off by the myriads of little chiraghs 

 used in this country for illuminating. 



Some of the plates I used were Taillefer's and the fact that from my 

 house, near the Cathedral, I was able to obtain a fairly clear impression 

 on the negative of the illuminations about Govt. House and the Post Office, 

 nearly two miles away, with 5 minutes' exposure and a not very rapid 

 lens, will shew how sensitive these plates are to faint yellow light. 



