146 Limited extent of man's senses. 



momentum of this Earth, is so exceedingly small that 

 it can hardly be conveyed to our minds by means of 

 figures ; even the steam engine, excessively wasteful 

 as it is of power, far surpasses him in strength. The 

 duration of his existence is to that of the world he in- 

 habits, as nothing to infinity. His power and speed 

 of locomotion are also very limited ; the globe to 

 which he is fixed by gravity, moves in one hour 

 through a distance greater than he could walk in 

 twenty years. Practically, by circumstances, he is al- 

 most rooted like a vegetable to the locality where he 

 exists ; comparatively few men have walked even a 

 hundred miles from their homes, or have been con- 

 veyed round this little globe by the aid of all our im- 

 proved means of transport. A balloon can ascend in 

 the air, but a man cannot ; without the aid of that 

 apparatus he is absolutely fixed to the surface of the 

 Earth, and with the assistance of all the appliances of 

 science, he cannot yet ascend even ten miles into the 

 atmosphere, nor dive more than a few fathoms into 

 the sea. His senses are equally contracted ; his per- 

 ceptions of touch and sound are far less delicate than 

 that of the microphone ; a photographic surface will 

 detect vibrations of light which he cannot at all per- 

 ceive, and record images more quickly than his brain ; 

 and for the detection of magnetism and the chemical 

 rays of light he possesses no sense whatever : electro- 

 meters and galvanometers can detect thousands of 

 times smaller quantities of electricity than he can per- 

 ceive : whilst a bolometer renders manifest a one 



