442 ON A MONOCHROMATIC LAMP FOR MICROSCOPES, &C. 



not only bright, but well denned in its boundaries. This dis- 

 tinct exhibition of the yellow space, established beyond a 

 doubt its existence in the spectrum, and may be considered as 

 proving, in a very convincing manner, that the Red and Green 

 spaces, at the place where they come in contact, consist of Red 

 and Green rays, respectively mixed with yellow rays of the 

 same refrangibility. The Yellow light, therefore, of the solar 

 rays, instead of occupying a separate place in the spectrum, 

 has its most refrangible rays mixed with green light of equal 

 refrangibility, and its least refrangible rays mixed with red 

 light of equal refrangibility. 



In order to ascertain whether or not the yellow homogene- 

 ous light produced by imperfect combustion, occupied the 

 same place in the spectrum with the yellow light, which re- 

 mains after the absorption of part of the red and green spaces, 

 I formed a spectrum like Dr Wollaston's, from the flame of a 

 candle, as shewn at AE, Plate XXVII. Fig. 3. I then put some 

 salt into the wick, for the purpose of producing a considerable 

 portion of yellow light, which affected principally the margin of 

 the upper and lower part of the flame, and I again observed the 

 spectrum, when I found that the yellow light occupied the posi- 

 tion at B &, so as to cover a part both of the green and the red 

 space ; the part of the green space occupied by the yellow light, 

 being to that of the red spaces occupied by it nearly as 3 to 1 . 

 From these experiments, we are entitled to conclude, not on- 

 ly that yellow light has an independent existence in the spec- 

 trum, when formed from any kind of white light ; but that the 

 prism is incapable of decomposing that part of the spectrum 

 •which it occupies. 



EXPLA- 



