52 ORIGIN AND NATURE OF LIFE 



short outline of spectroscopic investigation 

 becomes necessary. 



Each chemical element as it is raised to an 

 incandescent heat, or becomes radiant in a 

 vacuum bulb through which a high tension 

 electrical current is sent from an electric coil, 

 takes on a rate, or a number of rates, of 

 periodic vibration of its own of enormous 

 rapidity. As a result of this, the element 

 gives out light of a character peculiar to it. 

 This light when sent through a prism does not 

 form a continuous coloured spectrum in 

 which all colours are represented by light 

 waves of different frequency, but consists 

 rather of a number, few or many, of bright 

 lines. When a spectrum of the incandescent 

 element is obtained by passing the light 

 emanating from it through a spectroscope, 

 a series of distinctive bright lines is obtained 

 which discloses the identity of the element 

 as unmistakably to the spectroscopist as a 

 thumb-print does the identity of an individual. 

 Also, it is known, that if light from another 

 source, such as a gas burner, which would 

 otherwise give a continuous bright spectrum, 

 is passed through the vapour of an element 

 at a high temperature, then that element 

 absorbs just the light which it would itself 

 give out if it were incandescent, as described 



