THE SENSES OF INSECTS 117 



that the colours of objects and the general aspect of 

 nature must present to animals a very different appearance 

 from what it does to us. These considerations cannot 

 but raise the reflection how different the world may — I 

 was going to say must — appear to other animals from 

 what it does to us. Sound is the sensation produced on 

 us when the vibrations of the air strike on the drum 

 of our ear. When they are few the sound is deep ; 

 as they increase in number, it becomes shriller and 

 shriller ; but when they reach 40,000 in a second, they 

 cease to be audible. Light is the effect produced on 

 us when waves of light strike on the eye. When 400 

 millions of millions of vibrations of ether strike the 

 retina in a second, they produce red, and as the number 

 increases the colour passes into orange, then yellow, green, 

 blue, and violet. But between 40,000 vibrations in a 

 second and 400 millions of millions we have no organ of 

 sense capable of receiving the impression. Yet between 

 these limits any number of sensations may exist. We 

 have five senses, and sometimes fancy that no others 

 are possible. But it is obvious that we cannot measure 

 the infinite by our own narrow limitations." 



