Intelligence and Miscellaneous Articles. 75 



cone of blue light hardly reached an eighth of an inch beyond the 

 surface. The cell filled with the solution was placed opposite the 

 sky, and a photograph taken of it on iodide of silver with a quartz 

 lens : the sky, on developing, came out black, while the light which 

 had passed through the quinine had hardly affected the plate in 

 the least. I then diluted the solution, until, on trial, the cone of 

 light reached half way across the cell ; still the photograph pre- 

 sented the same appearance as before, and it was not until the solution 

 was so diluted that the cone of blue light, formed by concentrating 

 a ray of sunlight upon the solution, would pass completely through, 

 that I could perceive an increase in the effect on the photograph. 

 When the solution was no stronger than one or two grains to the ounce, 

 there were hardly any chemical rays absorbed. 



The slight effect which the light produced after passing through 

 the strong solution of quinine, I found to be due solely to the action 

 of the less refrangible rays. A photograph was taken of the solar 

 spectrum, the beam of sun-light being allowed to pass through the 

 above solution before falling upon the prism : there was a slight 

 impression, but only where the visible rays fell. The same effect 

 was produced on bromide of silver in a much shorter time. 



I immediately procured some collodion with bromine in the place 

 of iodine, prepared for me by Mr. Hockin ; this I found to answer 

 the purpose very well. 



On copying one of the figures seen in nitre on this film, inter- 

 posing a bath of a nearly saturated solution of sulphate of quinine 1^ 

 inch thick, I had the gratification of finding it as I had anticipated ; 

 the rings were now reduced to the visible number, and at the same 

 time were much broader, owing to the greater extent of surface in 

 each ring capable of affecting bromide of silver. But here a remark- 

 able dislocation presented itself ; each quadrant of the interior rings, 

 instead of retaining its usual regular figure, appeared as if broken in 

 half, the halves being alternately raised and depressed towards the 

 neighbouring rings. 



Having obtained such unexpected results with nitre — a crystal 

 possessing two axes — it became a matter of great interest to see 

 whether an abnormal figure would be shown by a uniaxial crystal 

 under similar circumstances. Calc spar was the one selected for this 

 purpose ; the figure which I had hitherto obtained on iodide of silver 

 was a perfectly regular one, the rings gradually diminishing in breadth 

 and distinctness as they became more distant from the centre, and dif- 

 fering in no respect from those seen in the polariscope but in ex- 

 tending to a much greater distance. When bromide of silver was 

 employed, and the quinine bath used to intercept the chemical rays, 

 the figure no longer presented so regular an appearance as at first ; 

 the number of rings was now reduced to about nine, while the fourth 

 and fifth seemed to unite together to form one large ring, entirely 

 obliterating the intervening space. 



I have since found that these effects are obtained whether the 

 quinine bath be present or not, whenever bromide of silver is em- 

 ployed as the sensitive surface. 



