440 ON A MONOCHROMATIC LAMP FOR MICROSCOPES, &C. 



green image from these adhering tints. The sulphate of cop- 

 per, even in thin laminae, exerts a very powerful action over 

 the red and violet extremities of the spectrum. See Fig. 4. 

 Nos. 6, 7, 8. 



In examining the spectrum with Yellow glasses, the Violet, 

 Blue, and Green rays are absorbed in succession, and the red 

 and yellowish-green remain untouched. By means of a very 

 thin plate of native yellow orpiment, the violet, and almost all 

 the Blue rays are absorbed, while the Red, and all the Green 

 are left. 



Heel glasses, like those which are Blue, do not attack the op- 

 posite extremity of the spectrum. They first absorb the blue 

 rays, then the violet, then the green and yellow \ and by in- 

 creasing their thickness, the red itself finally disappears. A 

 red glass, with a slight tinge of yellow, absorbed with great avidi- 

 ty the blue and green that are adjacent to one another, leaving 

 the violet in full force, and also the green adjacent to the red. 



2. In attempting to ascertain the influence of heat upon the 

 absorbing power of coloured media, I was surprised to ob- 

 serve that it produced opposite effects upon different glasses, 

 diminishing the absorbent power in one case, and increasing 

 it in another. 



Having brought to a red heat a piece of purple glass that 

 absorbed the greater part of the Green, the Yellow and the in- 

 terior, or most refrangible Red, I held it before a strong light, 

 and when its red heat had disappeared, I observed that the 

 transparency of the glass was increased, and that it transmitted 

 freely the Green, the Yellow, and the interior Red, all of which 

 it had formerly in a great measure absorbed. This effect, 

 however, gradually disappeared, and it recovered its former 

 absorbent power when completely cold. 



When a yellowish-green Glass was heated in a similar man- 

 ner, it lost its transparency almost entirely. In recovering its 



green 



