LIGHT AND COMFORT 361 



and is believed to be an electrical phenomenon in thin air. 

 The heights of the streamers have been calculated to be more 

 than a hundred, perhaps several hundred miles, so that it is 

 probable that air in a rare condition extends to this elevation. 



Theories Concerning Light. Although it is very easy 

 to perceive light and to examine many of its properties, 

 yet to determine just what it is that produces the light 

 sensation has been found vastly difficult. Sir Isaac New- 

 ton thought that light consisted of streams of very mi- 

 nute particles, or corpuscles, thrown off by the luminous 

 body. Since about 1800, it has been considered a form 

 of wave motion which is transmitted through the ether 

 which fills all space. 



Light and Comfort. In early days when few people were 

 able to get glass for windows, houses were dark and gloomy. 

 At present, however, glass is cheap and there is no reason 

 why houses should not be well lighted. Few houses are 

 built nowadays without making generous allowance for 

 window space. All modern manufacturing buildings have 

 the major part of their outside walls devoted to windows. 

 Hospitals are so planned that every possible room may have 

 direct sunshine for at least a part of every day. We are 

 beginning to appreciate the value of abundant sunlight. 



Dampness and darkness are the two conditions favorable 

 to the growth and activity of bacteria. Few disease germs 

 can live if exposed to the direct light of the sun. No house 

 can have too much sunlight. There should be no dark 

 corners to harbor germs. Kitchen cupboards and sinks 

 should be so located, if possible, that they may receive direct 

 sunshine. Bedclothes, rugs, hangings, clothing, should all 

 be exposed to the bright sunlight as often as possible. Sun- 



