52 SPECTRUM ANALYSIS OF FLAMES. [MEMOIR II. 



ready remarked, a colored ring, the red being the inner- 

 most color, and the violet outside; for if this be the 

 order in which the colors occur, the red ring must neces- 

 sarily have a less diameter than the green, and the green 

 less than the violet; and when the prism, set in a hori- 

 zontal position, separates those colors from each other, 

 the sides of the resulting spectrum ought not to be par- 

 allel, but inclined to one another, the breadth being least 

 in the red and increasing towards the violet end. This 

 increasing breadth proves that the constituent colored 

 shells of the flame envelop each other, the violet being 

 outermost, and therefore broadest. This valuable indi- 

 cation would be wholly lost if the slit were vertical. 



This being understood, I may illustrate the facts now 

 to be brought forward by an example of the prismatic 

 analysis of a horizontal element of the flame of a spirit- 

 lamp ; it being understood that the prism is at its angle 

 of minimum deviation, and the spectrum seen through 

 the telescope. All the prismatic colors, in their proper 

 order, are visible ; the sides of the spectrum not being par- 

 allel, the inclination being quite rapid towards the red 

 extremity, the rays of which come from the interior of 

 the flame, where the diameter is less. Mere inspection is 

 sufficient to show the rapid approach of the red sides to 

 each other, and I satisfied myself that even in the more 

 refrangible regions there is the same want of parallelism, 

 by rotating the telescope on its vertical axis so that the 

 vertical wires in its eye-piece might coincide with first 

 one and then the other side of the spectrum. It will be 

 understood that I took the proper precaution not to be 

 deceived by a partial want of achromaticity in the tele- 

 scope, which might have led to a mistake. 



But further, the yellow space of such a spirit -flame 

 spectrum is crossed by a bright fixed line Brewster's 

 monochromatic ray. It is a beautiful example of the 



