192 Domestic Science 



limits of our atmospheric envelope only extend outwards 

 from the Earth's surface to a distance of at most some 

 few hundred miles. Beyond this limit ether alone is 

 thought to be the medium by means of which the 

 vast gap is bridged, and the existence of the Sun 

 made evident to our senses by the light and heat 

 it affords. 



128. Ether being continuous, no motion of its 

 separate parts such as occurs in convection can be 

 assumed to be the means by which heat is propagated 

 through it. An entirely different form of motion, the 

 up and down vibration we usually term wave-motion, 

 is the method suggested. The light and heat emanating 

 from the Sun set up this form of motion in the ether, 

 the waves produced being exceedingly minute so 

 minute that many thousands of them are caused in 

 so short a distance as one millimetre. These light 

 and heat waves are simply ether in motion and the 

 ether itself is neither illuminated nor heated by the 

 passage of light and heat in this manner. When waves 

 of a certain size strike an object, the sensitive mem- 

 branes of the eye are affected and we see the object, 

 by reason of the reflection of some of the waves towards 

 the eye. Waves of a somewhat greater size do not 

 excite the sensation of vision when they reach an 

 object, but become evident to us by causing the object 

 to become hot. We can now understand why the 

 hand, placed beneath or at the side of a hot body, 

 receives heat from the body, although, as previously 

 stated, the heated air travels upward. The heat experi- 

 enced by the hand situated underneath the hot object 

 reaches it by setting up heat waves in the ether between 

 the air molecules, and when these impinge upon the 

 hand, the sensation of hotness is excited. That the 



