102 Prof. Draper oji the Prodtecttori of Light 



be made, pass through a horizontal slit 3^jjth of an inch wide 

 and one inch long in a metallic screen, and are received at a 

 distance of six or eiglit feet on a flint-glass prism, the axis of 

 which is parallel to the slit. After passing the prism they 

 enter a small telescope, which has a divided micrometer, and 

 also parallel wires in its eye-piece. Through this telescope the 

 resulting spectrum is viewed. 



If it be the flame of a lamp of any kind that is to be ex- 

 amined, by using a moveable stand we are able to raise or 

 lower it, and thus analyse different horizontal elements in its 

 lower, its middle, or its upper part at pleasure. If, instead of 

 a horizontal, we wish to examine a vertical element of the flame, 

 the slit and the prism must of course be set verticall}'. The 

 former mode possesses great advantages, as will be presently 

 pointed out. It is to be understood, in all cases, that the eye- 

 piece of the telescope is adjusted to give a sharp image of the 

 slit, and the prism is at its angle of minimum deviation. 



By this arrangement I have examined a great number of 

 different flames; as those of oil, alcohol, solution of boracic 

 acid and nitrate of strontian in alcohol, phosphorus, sulphur, 

 carbonic oxide, hydrogen, cyanogen, arseniuretted hydrogen, 

 &c. Among these it will be noticed different colours occur. 

 Oil gives a yellow flame, alcohol a pale blue, boracic acid 

 green, strontian red, phosphorus yellowish-white, sulphur and 

 carbonic oxide blue, hydrogen pale yellow, cyanogen lilac, 

 arseniuretted hydrogen white, &c. 



Notwithstanding this diversity of colour, all these flames, as 

 well as many others I have tried, yield the same result : every 

 prismatic colour is found in them. Even in those cases where 

 the flame is very faint, as in alcohol and hydrogen gas, not 

 only may red, yellow, green, blue, and violet light be traced, 

 but even bright Fraunhoferian lines of different colours. 



This observation holds good for those flames reputed to be 

 monochromatic; for example, alcohol burnt from a wick im- 

 bued with common salt. It is not alone a yellow light which 

 is evolved ; the other colours plainly, though more faintly, 

 appear. 



All flames, no matter what their primitive colours may be, 

 evolve all the prismatic rays. Their special tints arise from 

 the preponderance of one class of rays over another; thus in 

 cyanogen the reds predominate, and in sulphur the blues. 



The production of light, in the case of flames, is thus proved 

 to be a very complex phaenomenon. The chemical conditions 

 under which their burning takes place are likewise very com- 

 plex. The combustible vapour is surrounded on all sides by 

 atmospheric air: diffusion occurs, and rapid currents are 



