194 CELESTIAL DISSOCIATION. 



ever devised by the brain and hand of man; and that if 

 we are to win additional knowledge of elemental dissocia- 

 tion as it exists in the sun and stars, the spectroscope is 

 our one sole means to that end. 



On a priori grounds we should rather expect to find this 

 dissociation. For the elements which dissociate on earth, 

 thorium for example, are in their normal chemistry, in no 

 wise remarkable or particularly distinguished from other 

 elements. The other elements, therefore, ought to dis- 

 sociate under favorable conditions. Now, it is in the sun 

 and stars that we shall find these favorable conditions if 

 anywhere; for they constitute furnaces with temperatures 

 enormously high and transcendental so far as man may 

 hope to attain. The spectroscope with which we shall 

 search for this celestial dissociation is, in its essentials, sim- 

 ple in the extreme. The fundamental part of the instru- 

 ment is a prism of glass or a grating. The light from the 

 body under examination is passed through a fine slit and 

 hence through the prism. The prism sifts out the light so 

 that the longest or " red " waves go to one side and the 

 shortest or "violet" waves to the other. Each kind of 

 light thus yields its own individual image of the slit in the 

 form of a fine line. All incandescent solids, liquids, and 

 some dense gases on becoming incandescent give out white 

 light consisting of waves of every conceivable length and 

 hence instead of separate little line-like images there results 

 an infinity of images all blended together into a broad band 

 ranging by imperceptible gradations through red, orange, yel- 

 low, green, blue and violet. Such a band of color is called 

 a continuous spectrum. Fig. 45. If, now, we pass from 

 incandescent solids and liquids to substances which easily 

 volatilize, the light from their flames presents a very dif- 

 ferent appearance. We find, in fact, that it consists of a 



