THE SPECTROSCOPE. 497 



holding a cold body, such as a piece of metal, in the 

 flame ; the carbon particles which come in contact with 

 the metal are thereby cooled, the further combustion is 

 thus prevented, and they are deposited on the surface of 

 the cold body as ' soot/ 



The most important fact that has been demonstrated by 

 the decomposition of light into rays of various colours, 

 in the manner above described, is that the spectrum 

 consists of a series of images of the flame, each of which 

 is produced in a different position from the rest, in con- 

 sequence of the refrangibility of those rays by which it 

 is formed being different from that of the rays form- 

 ing any of the other images. For further investiga- 

 tions into the decomposition of light a special kind of 

 apparatus is used, called a spectroscope ; the mode of 

 resolving light by means of it is termed spectrum 

 analysis. 



Spectroscopes intended for more refined investiga- 

 tions present great varieties of construction, and are 

 complicated and expensive. They consist of a train of 

 prisms which considerably increases the dispersion, and 

 of an optical arrangement of various lenses which en- 

 ables the observer to view the spectrum as through a 

 telescope, instead of using the naked eye. For our 

 purpose a simple spectroscope is sufficient, consisting 

 of a disulphide of carbon prism, a slit, and a box for 

 keeping off stray light. 



When a narrow vertical slit is interposed between 

 the source of light and the eye, the whole flame is no 

 longer seen, but a thin line of light, or a number of such 

 lines side by side, if the light consists of various colours. 

 These fine lines will not so easily merge into one another 



K K 



