52 INTRODUCTION TO GENERAL SCIENCE 



3. Change in chemicals, which enable us to use the art of 

 photography, and other changes, a study of which belongs 

 particularly to a chemistry course. 



4. In plants also, much of the growth, and nearly all of the 

 nourishment, are dependent upon chemical changes which the 

 energy of the sun causes in them. Plants cannot take up the 

 carbon from the air, nor can they change starch to sugar, 

 necessary for plant growth, without the sunlight or some 

 other very powerful light, as, for instance, the electric arc. 



5. Electrical energy from the sun probably causes terres- 

 trial magnetism. It has been noticed whenever there are sun 

 spots that the magnetism is affected, proportionally to the 

 size and duration of the sun spots. In this connection it is 

 quite likely that the aurora borealis and the aurora australis 

 owe their existence to the same cause. 



References : 



1. 1002 : 414-416. Description of Sun Spots. 



2. 1103 : 27. Solar Constant. 



a. 1001:124-127. Nature of Sun Spots. 



6. 1001 : 131-132. Cause and Influence of Sun Spots. 



c. 1003:106-110. Sun Spots Show Rotation of Sun. 



d. 1004 : 143-144. Terrestrial Influence of Sun Spots. 



e. 1207 : 74-75. Explanation and Effects of Sun Spots. 

 /. 1301 : 53-54. Magnetism and the Northern Lights. 

 g. 1306 : 8. Sun Spots. 



h. 1806 : 376-378. The Sun our Main Source of Energy. 



36. THEORIES 



From time immemorial, man has wondered about the laws 

 and phenomena of nature. His conjectures, somewhat hazy 

 at first, and more scientific as the ages passed, always con- 

 cerned the same questions : the source of the world; why the 



