80 



REPORT — 1853. 



(126). Avery intense spectrum was 

 produced by a good achromatic lens 

 employed in my camera obscura for 

 photographic purposes. The result- 

 ing chemical spectrum without the 

 interposition of any absorbed me- 

 dium was that shown in fig. 59 ; the 

 second image being the result of the 

 interposition of the quinine screen, 

 the exposure in each case being pre- 

 cisely one minute. Upwards of 

 twenty spectra were obtained in the 

 same morning, and, as a constant re- 

 sult, the above woodcut maj' be re- 

 garded as a faithful representation. 



(127). I was anxious to ascertain 

 the relative differences between the 

 spectra obtained on the iodide of 

 silver and those impressed on the 

 bromide. The paper was first 

 washed with a solution of bromide of 

 potassium, 117 grs. to six ounces of 

 water; then with nitrate of silver, 

 170*57 grains to three ounces of 

 water. The spectrum being care- 

 fully thrown on the paper by nice 

 adjustment of the prism, &c., it was 

 washed with weak gallo-nitrate of 

 silver, the spectrum being shut off ' 

 by an opake screen. The screen 

 being removed, the luminous 

 image was allowed to act for one 

 minute, and was then again ob- 

 structed. Fig. 60 shows the che- 

 mical image of the spectrum 

 which had not undergone any 

 absorption, and the second that 

 which was obtained when the 

 quinine trough was interposed. 



(128). It has been repeatedly ^ 

 stated that the rays at the most — 

 refrangible end of the luminous 

 spectrum were rendered chemi- 

 cally inactive by the quinine solu- 

 tion. When bromide of silver is 

 employed, this, as is shown in fig. 

 60, has been a constant result ; 

 but in no case where the iodide of 

 silver has been employed has this 

 been found to be the case. 



(129). In conclusion, I may state, 

 that M'ith a view of determining 

 by another method the extent to 

 which the chemical action of the 

 solar radiations were obstructed ^' 



Fig. 59. 



1 



Fig, 60. 



