102 PHYSICAL SCIENCE BK. n 



vents continuity in the fire. As often as the air 

 by its more violent agitation sets itself on fire it 

 conceives an impulse toward flight. When the 

 internal conflict has been ended by its escape, it is 

 afterwards for the same reason sometimes carried 

 down as far as the earth, and sometimes, if urged 

 down with less force, it is dissipated in air. Why, 

 again, is the course of the lightning oblique ? The 

 reason is that the air current of which it is composed 

 3 is oblique and tortuous. Nature summons fire up- 

 ward, violence presses it downward, and so it begins 

 to be zigzag. Sometimes, when neither force gives 

 way to the other, the fire is at the same moment 

 urged toward the upper and depressed toward the 

 nether regions. Why are the peaks of mountains 

 frequently struck by it ? Because they are exposed 

 to the clouds, and objects falling from heaven to earth 

 must pass by way of them. 



LIX 



1 I KNOW quite well what you have- long been anxious 

 to say and what you demand. I had rather, you 

 say, get rid of fear of thunderbolts than learn all 

 about them. So you may reserve for others your 

 instruction regarding their origin. Let me be 

 delivered from fear of them rather than be informed 

 of their nature. Well, I will follow your invitation, 

 for I quite allow that some moral should be attached 



2 to all studies and all discourse. As we dive into 

 the secrets of nature and treat of things in the 

 heavens, the soul must be delivered from its errors 

 and from time to time reassured. Even the learned 

 who devote themselves exclusively to this pursuit 

 require such reassurance ; not in order to escape 



