THE SUN THE SOURCE OF ALL ENERGY 51 



h. 1207 : 253-257. The Sun as a Source of Heat. 



i. 1301 : 55-57. Heat of Sun. 



j. 1807 : 211. Source of the Sun's Energy. 



k. 1810 : 398. Composition of the Sun. 



35. THE SUN THE SOURCE OF ALL ENERGY 



As previously stated, the sun sends out energy, which is 

 transformed into various other kinds of energy. It is quite 

 probable that the original energy is electrical, and that its 

 products depend upon the various conditions it meets. These 

 products may be enumerated as follows : 



1. The Sensation of Light. Light in itself is invisible. Cer- 

 tain wave lengths of electrical energy enter the eye and pro- 

 duce their effect, according to the length of the waves, and the 

 amount of energy which affects the retina, or sensitive part 

 of the eye. We see objects by reflected light. We really do 

 not see the objects themselves. All light produced on earth 

 owes its energy originally to the sun. 



2. Heat. This is produced when the electrical energy 

 strikes anything which retards it. If it strikes an opaque 

 object, all the energy is stopped, and the result is the great- 

 est possible amount of. heat. If the object is transparent, 

 most of the energy will pass through; very little will be 

 stopped, and the material will not become very warm. The 

 amount of heat produced by the energy of the sun varies from 

 a very little, in the case of transparent material, to a great 

 deal, in the case of opacity. An excellent example of this is 

 to notice how warm we become when we stand by a closed 

 window in the sunshine, and then to observe that the glass, 

 through which this energy comes, is quite cold. This is ab- 

 solute proof that heat from the sun does not come to us as 

 heat, but as energy, which is doubtless electrical. 



