456 ON THE ABSORFTION OF LIGHT BY COLOURED MEDIA, 



its cup, or, rather, like a rose-bud from its enveloping calyx. 

 The yellow cone extends only about two-thirds of the way 

 down ; and the bottom, or purely blue portion of the flame, 

 emits no yellow rays ; its type, when examined with the prism, 

 being as in Fig. 12., consisting of an ill-defined train of red, a 

 bright but undefined green, with masses of blue and violet 

 light varying in their character. The middle portion of the 

 flame, whose light emanates at once from the blue envelope 

 and the yellow cone, has the same type, with the addition of a 

 bright yellow spectrum, as marked by the dotted line in 

 Fig. 12., while the upper portion of the flame consists of light 

 perfectly homogeneous, and corresponding to the less refran- 

 gible portion of the yellow, as denoted by the dotted line 

 alone. Its tint is visibly more inclining to orange than that 

 of the yellow in the solar beam, and it is extremely enfeebled 

 by the interposition of the glass described in Art. 8., which 

 transmits the latter so readily. 



If the flame of a spirit-lamp be viewed through a glass con- 

 sisting of a pale-orange and a pale-green one, cemented toge- 

 ther, the light ti'ansmitted is homogeneous, and if inclosed in 

 a lanthorn of such combined glass, may be used as a mono- 

 chromatic lamp. 



15. The tinges given to the flame of alcohol by different sa^ 

 line combinations are well known, but have never been de- 

 scribed with any exactness, though some of them present re- 

 markable peculiarities. 



If muriate of strontia be the salt held in solution, the 

 flame assumes a beautiful carmine-red colour. When viewed 

 through a prism, with the usual precautions to diminish the 

 angular breadth of the incident pencil, a broad^ but Well- 

 detined red, and a narrow yellow image, are perceived sepa- 

 rated 



