in Energy, the Power of Nature 39 



there is a blank or black line. The same is true with the 

 vapours of all the other elements, the particular waves 

 absorbed differing in each case. Spectrum Analysis is a 

 term used to describe the discovery of the elements whose 

 vibrations give out a certain kind of light. It is not only 

 analysis or unloosening ; it is also a method of seeing 



FIG. 8. Diagram of the solar spectrum, showing the order of colour and the 

 position of the principal absorption lines. 



through a compound when taken apart by the action of heat. 

 However distant a body may be, if it gives out light, the 

 light tells its own tale as to the matter whose quiverings 

 sent waves through the ether, and as to any other kinds 

 of matter which may have exercised absorption on it in 

 intermediate space. 



64. Light and Colour. White light is produced when 

 waves of radiant energy corresponding to all or nearly all 

 the wave-lengths that affect vision strike the eye together. 

 When waves of light fall upon any object, some of them are 

 absorbed and the others are reflected ; the report these 

 reflected rays convey through the optic nerve to the brain 

 names the colour of the object. Thus when sunlight falls 

 on grass the rays whose vibrations produce the effect of 

 red, yellow, blue, and violet are almost all absorbed, their 

 energy being set to do work in the plant ( 399), and only 

 those which produce the sensation of green are sent back 

 to the eye. Similarly when light falls on a sliced beetroot 

 the yellow, green, blue, and violet-producing vibrations are 

 absorbed and only the red-producing rays sent back. When 

 light falls on a piece of charcoal it is all absorbed, and as 

 none is reflected the body appears devoid of light, or black. 

 A sheet of paper, on the other hand, absorbs very little of 

 the light and reflects white light as white. The fact that 



