THE PHENOMENA OF LIGHT 



347 



light energy as a series of waves in this medium. The number of these 

 waves per second (the wave frequency) may so vary as to give rise to 

 all manner of wave lengths entering the eye from a luminous body. 

 The eye, however, responds to only a relatively narrow range of these 

 ether impulses. It recognizes but seven different colors or color groups 

 in the solar spectrum. There is no sharp line of separation of these 

 colors from one another. 



FIG. 115. Dispersion of light as it enters at D, and again as it leaves a 

 falling raindrop at V'R'. The internal reflection of this light at RV rather 

 than its transmission through and beyond the falling drop makes possible a 

 rainbow in the east when the sun is in the west in late afternoon. (Tower, 

 Smith & Turlon.) 



The great variety in colors coming from bodies results from the 

 blending of different wave lengths in different proportions, giving rise 

 to color sensations of a composite character. 



It is quite possible that there are other forms of energy transmitted 

 through the ether medium unrecognized by man because of a lack in 

 his own body of any "receiving apparatus." Advances in science may, 

 however, succeed in arresting and so transforming any such forms 

 that their existence and nature will become apparent. Wireless teleg- 

 raphy, and the use of the dynamo for the production of electric cur- 

 rents, are illustrations of the uses made by inventors of the discoveries 

 of scientists. The discovery of "X-rays" and of radium, and the 



