LIGHT 121 



light given by a sperm candle burning about 8 grams of wax 

 an hour. A common type of incandescent electric light is 

 the 16-candle-power light, which gives about as much light 

 as 16 standard candles. 



131. Vision. It is often said that we "see light/' but 

 that is not strictly true. The fact is that we see an object 

 which gives light, or we look into a room which is lighted. 

 We see bodies which send light to the eye. 



Air, clear water, and glass are the ordinary mediums 

 through which light passes. Such substances are called 

 transparent. Horn, celluloid, and ground glass are semi- 

 transparent or translucent. An opaque substance is one 

 through which light does not pass; as brick, wood, and 

 stone. 



132. Light, a Form of Energy. Light, like heat, is a 

 form of energy, for it does work, although the work is not 

 always immediately observed. The change or loss of color 

 called fading, with which all are familiar, is due to light. 

 We know that the exposure of a photographic film to the 

 light for a small fraction of a second, makes the film different 

 in some way. It is possible to produce a picture from it 

 afterward by the application of the proper solutions. The 

 energy of light has rearranged molecules on the film and 

 formed new compounds. 



The important work of starch making is carried on in the 

 green leaves of plants only in sunlight. The light energy 

 used in that process is later transformed into heat energy 

 or muscular energy in the animals using the plants as food. 

 Energy is never lost or destroyed, though often it is so 

 changed that the ordinary observer does not recognize it. 



Light which falls upon a body from any source may be 

 transmitted, passed through the body; reflected, turned 

 away; or absorbed, taken in. Absorption of light raises 

 the temperature of the absorbing body; that is, light energy 

 is transformed into heat. Sunlight is transmitted through 



