HOW HEAT AND LIGHT DIFFER 147 



The particles of heat-giving and light-giving bodies are in 

 a state of rapid vibration, and thereby disturb the sur- 

 rounding medium, which transmits or conveys the disturb- 

 ance to the earth or to other objects by a train of waves. 

 When these waves reach their destination, the sensation of 

 light or heat is produced. 



We see the water waves, but we can never see with the eye 

 the heat and light waves which roll in to us from that far- 

 distant source, the sun. We can be sure of them only through 

 their effect on our bodies, and by the visible work they do. 



140. How Heat and Light Differ. If heat and light are 

 alike due to the regular, rapid motion of the particles of a 

 body, and are similarly conveyed by waves, how is it, then, 

 that heat and light are apparently so different ? 



Light and heat differ as much as the short, choppy waves 

 of the ocean and the slow, long swell of the ocean, but not 

 more so. The sailor handles his boat in one way in a choppy 

 sea and in a different way in a rolling sea, ior he knows 

 that these two kinds of waves act dissimilarly. The long, 

 slow swell of the ocean would correspond with the longer, 

 slower waves which travel out from the sun, and which on 

 reaching us are interpreted as heat. The shorter, more fre- 

 quent waves of the ocean would typify the short, rapid waves 

 which leave the sun, and which on reaching us are interpreted 

 as light. 



