Intelligence and Miscellaneous Articles. 73 



suggestion contained in the paper is a valid step towards it, is treated 

 with doubt and left to opinion. 



May 9. — Mr. Hopkins, F.R.S. &c., the President of the Society, 

 gave an account of some experiments for the determination of the 

 temperature of fusion of different substances under great pressure ; 

 and on the application of the results to ascertain the state of the 

 interior of the earth. 



IX. Intelligence and Miscellaneous Articles. 



ON THE APPLICATION OP PHOTOGRAPHY TO THE STUDY OF CER- 

 TAIN PHENOMENA OP POLARIZATION. BY MR. W. CROOKES*. 



THE experiments which I have the honour to submit to the Society 

 this evening were commenced about eighteen months ago, and had 

 their origin in the desire to record and retain in a more tangible form 

 the well-known beautiful figures observed when thin slices of some 

 crystals (such as calc spar and nitre) are seen in the polariscope. 



After several preliminary trials with different arrangements of lenses 

 and tourmalines, in the endeavour to produce a well-defined image on 

 the ground-glass of the camera, I finally proceeded in the following 

 manner : — The erystal to be copied was placed between two tourma- 

 lines, and adjusted by looking through them at any diffused light ; 

 when the proper figure was obtained, the whole was cemented together 

 with marine glue, and fastened in the brass-tube of a double achro- 

 matic portrait-lens. Several lenses (non-achromatic) were placed 

 behind the crystal to receive the image and reduce its size before fall- 

 ing upon the collodion plate ; these varying in number and focal length, 

 according as the image was required large or small. A lens was 

 placed in front of all, more as a protection against dust, &c. than 

 for any practical purpose ; it seems, however, to condense the light 

 a little. Although this arrangement produced a very perfectly defined 

 figure upon the ground-glass, the light was so exceedingly faint, 

 having to pass through so many thicknesses of glass, besides two 

 dark-brown tourmalines not a quarter of an inch square, that no 

 image could be perceived on the focusing-glass unless the camera was 

 held pointed direct to the sun, and every other light carefully excluded 

 from the eye. Collodion, although so exquisitely sensitive under ordi- 

 nary circumstances, was quite inadequate to copy these figures, as the 

 plates, in their necessarily upright position, would not bear the long 

 exposure requisite to obtain a picture without spontaneously decom- 

 posing; besides which, the camera being pointed at the sun, the motion 

 of the latter would produce a very unequal action on the plate, fatal 

 to the success of the experiment. After repeated trials and as many 

 failures, I was obliged to substitute sensitive paper for the collodion 

 plate, and leave the camera pointed for several days to the north. In 

 this experiment, although I obtained no very good result, I had the 



• From the Journal of the Photographic Society for June 21, 1853 ; 

 having been read before the Society June 2. 



