i 9 2 Human Physiology. 



nature to satisfy the sense of sight ! Before it is spread out all the 

 beauty of the earth and all the glory of the firmament. Nature 

 and art exist for the eye, and the eye makes nature visible to 

 us and art possible. Through this sense we feel what is dis- 

 tant, we reach to the stars, and, assisted by the telescope, which 

 is only an enlargement or extension of the eye itself, we see 

 myriads of worlds which had else remained invisible. In a 

 similar way, improving the scope of our eyes in another direc- 

 tion, we are able to scan new worlds of the infinitely little, and 

 examine myriads of creatures of which but for the microscope 

 we should never have known the existence. 



Sight, in civilised man, though improved by his inventions, 

 has lost much of the power it has in many animals and the 

 more simple races of men. Birds of prey, and those that feed 

 on carrion, from great heights in the air are able to see small 

 objects over a vast extent of territory. Let an animal fall dead 

 on a tropic plain, and in a few moments vultures are seen fly- 

 ing from different directions, which were previously quite out 

 of the range of human vision. Think of all the objects of such 

 a vast area being painted upon the retina of a bird, so as to 

 convey to his mind the distinct idea of a living or dead animal 

 on any part of it ! A sailor sees a ship at sea when a lands- 

 man sees nothing but the waste of waters. The Arab espies a 

 camel when it is but a dot on the edge of the horizon, and on 

 his retina must be of minuteness inconceivable. 



Sight is the highest, the finest, the most perfect of the senses. 

 We hear by atmospheric vibrations, but we see by infinitely finer 

 vibrations of the luminiferous ether which pervades all space- 

 We can hear only sounds coming from a moderate distance, a 

 few miles ; we see, or receive the impressions of light vibra- 

 tions which come thousands of millions of miles. These vibra- 

 tions, excited by the action of some force in sun and stars, 

 reflected by all the objects around us, break in waves of light 

 upon the spread out nerves of vision, as the atmospheric sound 



