152 ON THE OEIGIN OF THE PLANETAKY SYSTEM. 



The formation of the prismatic spectrum depends on 

 the fact that the sun's light, and that of most ignited 

 bodies, is made up of various kinds of light, which 

 appear of different colours to our eyes, and the rays 

 of which are separated from each other when refracted 

 by a prism. 



Now if a solid or a liquid is heated to such an 

 extent that it becomes incandescent, the spectrum 

 which its light gives is, like the rainbow, a broad 

 coloured band without any breaks, with the well-known 

 series of colours, red, yellow, green, blue, and violet, 

 and in no wise characteristic of the nature of the body 

 which emits the light. 



The case is different if the light is emitted by an 

 ignited gas, or by an ignited vapour that is, a sub- 

 stance vaporised by heat. The spectrum of such a 

 body consists, then, of one or more, and sometimes 

 even a great number, of entirely distinct bright lines, 

 whose position and arrangement in the spectrum is 

 characteristic for the substances of which the gas or 

 vapour consists, so that it can be ascertained, by means 

 of spectrum analysis, what is the chemical constitution 

 of the ignited gaseous body. Gaseous spectra of this 

 kind are shown in the heavenly space by many 

 nebulae; for the most part they are spectra which 

 show the bright line of ignited hydrogen and oxygen, 

 and along with it a line which, as yet, has never been 



