154 Photographs of the red end of the Spectrum. [April, 



Hon. Justice Gurudas Banerji, M. A., D. L., proposed by Babu 

 Gaurdas By sack, seconded by Lieut.- Col. J. Waterhouse. 



The following gentleman lias intimated his wish to withdraw from, 

 the Society : 



Babu Tara Prosad Chatterjee. 



The President announced the presentation by T. R. Munro, Esq., 

 of two enlarged photographs, framed, of plans of Calcutta, one from 

 drawings made in 1723 or 1724 showing the palisaded enclosure within 

 which the Christian community resided, and the other from a survey of 

 the town made in 1753 by Lieut. Wills, in command of the Artillery in 

 Bengal. 



Also the receipt from Count Landberg, Secretary General of the 

 Congress, of copies of the Programme -of the eighth International Con- 

 gress of Orientalists, to be held at Stockholm and Christiania in Sep- 

 tember next, with a request that they might be distributed amongst the 

 members of the Society — and stated that Monsieur Senart had been 

 asked to represent the Society at the Congress. 



The President exhibited some photographs of the red end of the 

 spectrum from C to Z taken with Rowland's plane and concave diffrac- 

 tion gratings and said : — 



In November 1875, I exhibited to the Society some photographs of 

 the red end of the spectrum about A and a short distance below it, 

 obtained on dry collodio-bromide of silver plates stained with anilin 

 blue and given a momentary exposure to white light before being acted 

 on by the spectrum. In these photographs, however, it was noticeable 

 that under the influence of the red as well as of the blue rays the image 

 of the spectrum was strongly reversed, i. e., instead of being a photogra- 

 phic negative it was a positive showing the lines as dark lines on a clear 

 ground. The photographs now before you are on gelatine dry plates stain- 

 ed also with a blue dye, but they show no traces of this reversal in any 

 part of the spectrum, and not only extend much further into the infrared 

 region, but show infinitely better definition and greater dispersion in . 

 this part of the spectrum owing to the employment of gratings in place 

 of prisms. 



The dye I have used for staining these plates is Alizarin Blue (G 17 

 H 9 N0 4 .), the quinoline of Alizarin. It is prepared from nitro-ali- 

 zarin by heating it with glycerine and sulphuric acid, and is found in 

 commerce as a paste insoluble in water and only slightly so in alcohol. 

 It dissolves in liquor ammonia with a greenish-blue colour. By mixing 

 the paste with a concentrated solution of sodium bisulphite the dye 



