xx CAUSES AND EFFECTS 69 



few of the clouds, but is buried beneath an 

 accumulation of them ? So fire will pass into air, and 

 lose its shining appearance in cutting through some 

 cloudy obstacles and kindling what is within. Add 

 now another inevitable result the rush of the 

 thunderbolt sends out blasts of air and drives them 

 before it, and raises a wind behind it through 

 the great extent of its impact on the atmosphere. 

 Thus, through the vibration caused by the wind 

 which the fire drives in front of it, all objects 

 quiver before they are actually struck by the bolt 

 of lightning. 



XXI 



WE must now dismiss our tutors and try to walk i 

 alone as we pass on from what is admitted to what 

 is debatable in this subject. What is to be classed 

 as admitted ? It is admitted that the thunderbolt 

 is fire of some kind ; similarly with the lightning 

 flash, which is simply flame ready to become a bolt 

 if it had more strength. The difference between 

 the two is not in character but in force. The fiery 

 nature of the bolt is proved by its heat. Apart 

 from that, its effects prove it, for it has often been 

 the cause of great conflagrations. Forests and 2 

 portions of cities have been burnt to ashes by it. 

 Even objects that are not struck are yet seen to 

 be scorched, some are discoloured as if by smoky 

 grime. Then, again, everything that lightning 

 strikes has the smell of sulphur. And so it is 

 beyond dispute that both phenomena are a form of 

 fire, and that they differ merely in their method of 

 movement. A flash is a bolt that has not strength 3 

 to carry it down to the earth. And conversely you 



