134 Dr BREWSTER on a New Analysis of Solar Light. 



yellow by means of a yellow transparent wafer, which absorbs 

 some of its blue rays, and green by a green transparent wafer, 

 which absorbs some of its red rays. 



From these experiments it follows, that white light, composed 

 of red, yellow, and blue rays, exists in the most luminous part of 

 the spectrum, on the most refrangible side of the line D, and 

 may be insulated by absorbing the excess of yellow light, and of 

 any of the other colours above what is necessary to compose white 

 light. In applying a highly dispersing prism, it was a singular 

 and peculiarly interesting sight to witness, for the first .time, a 

 beam of white light, consisting of red, yellow, and blue rays of 

 equal refrangibility, and incapable of being analyzed by prismatic 

 refraction. 



The preceding observations contain only a few out of a great 

 number of experiments which I have made on the absorptive ac- 

 tion of natural and artificial crystals, and of various fluids and un- 

 crystallized solids which possess either a natural or an artificial 

 colour. I made a few experiments with the coloured juices of 

 several hot-house plants, which Mr FORBES was so good as to pre- 

 pare for me ; and I expected, in the course of the summer, to 

 obtain by this means, a more striking insulation of some of the 

 simple colours, than I had effected by the substances within my 

 reach. Impatient, however, of so long a delay, I thought of sup- 

 plying the place of these absorbing fluids by forming the spec- 

 trum out of common or polarized light, which had undergone 

 the periodical action of thin plates in crystallized lamina?, or, 

 what is the same thing, by examining the spectrum through such 

 films and lamina? which have the property of transferring to the 

 reflected pencil certain alternate portions of the spectrum, while 

 all the intermediate portions appear in the transmitted rays. By 

 this means I was enabled to divide the spectrum into any num- 

 ber of stripes, alternately obscure and coloured, so that each of 



