26 Colouration in Animals and Plants. 



fall upon other matter, heat is the result. Thus heat, light and 

 chemical action are but phases, expressions, effects or results of 

 the different influences of waves upon different kinds of matter. 

 The same waves or billows will affect the eye itself as light, the 

 ordinary nerves as warmth, arid the skin as chemical action, in 

 tanning it. 



Though we cannot see these waves with the material eye, they 

 are visible indeed to the mental eye ; and are as amenable to 

 experimental research as the mightiest waves of the sea. Still, to 

 render this subject clearer, we will use the analogy of sound. A 

 musical note, we all know, is the effect upon our ears of regularly 

 recurring vibrations. A pianoforte wire emits a given note, or in 

 other words, vibrates at a certain and constant rate. These vibra- 

 tions are taken up by the air, and by it communicated to the ear, 

 and the sensation of sound is produced. Here we see the wire 

 impressing its motion on the air, and the air communicating its 

 motion to the ear; but if another wire similar in all respects is 

 near, it will also be set in motion, and emit its note ; and so will 

 any other body that can vibrate in unison. Further, the note of 

 the pianoforte string is not a simple tone, but superposed, as it 

 were, upon the fundamental note, are a series of higher tones, 

 called harmonics, which give richness. Now, a ray of sun-light 

 may be likened to such a note ; it consists not of waves all of a 

 certain length or velocity, but of numbers of waves of different 

 lengths and speed. When all these fall upon the eye, the sensation 

 of white light is produced, white light being the compound effect, 

 like the richness of the tone of the wire and its harmonies ; or we 

 may look upon it as a luminous chord. When light strikes on any 

 body, part or all is reflected to the eye. If all the waves are thus 

 reflected equally, the result is whiteness. If only a part is reflected, the 

 effect is colour, the tint depending upon the particular waves 

 reflected. If none of the waves are reflected, the result is 

 blackness. 



Colour, then, depends upon the nature of the body reflecting 

 light. The exact nature of the action of the body upon the light 

 is not known, but depends most probably upon the molecular con- 

 dition of the surface. Bodies which allow the light to pass through 

 them, are in like manner coloured according to the waves they 

 allow to pass. 



We find in nature, however, a somewhat different class of 



