ID PHYSICAL SCIENCE BK. i 



shock is less severe, and the atmosphere is merely 

 grazed, as it were, smaller lights are emitted, 



And the flying stars drag their hairy tail. 



5 Then their thin fires mark a slender path, which they 

 prolong across the sky. For that reason no night is 

 without sights of the kind ; no great movement of 

 the atmosphere is required to produce them. In 

 fact, to put it shortly, they are due to the very same 

 cause as thunderbolts, only they require less force. 



Clouds that encounter each other with little force 

 cause flashes of lightning ; if impelled by greater 



6 violence, thunderbolts. Aristotle offers the following 

 explanation : The earth gives forth many different 

 exhalations, some moist, some dry, some cold, some 

 containing the seeds of fire. And little wonder if the 

 earth s evaporation is of all varied kinds. Why, 

 even in the heavens the colour of objects does not 

 show uniform ; the red of the Dog-star is brighter, 



7 that of Mars duller ; Jupiter has no red, his sheen 

 is prolonged into pure light. Well, in the great 

 abundance of minute bodies emitted by the earth 

 and driven up to the higher regions, of necessity 

 some of the elements that reach the clouds furnish 

 material for fires. They do not require any collision 

 in order to burn, the breath of the sun s rays is 

 sufficient to kindle them. So with us, shavings 



8 sprinkled with sulphur catch fire at some distance. 

 Probably, therefore, tinder of this kind gathering 

 within the clouds is easily kindled ; greater or less 

 fires are produced just as there has been more or 

 less substance in the elements. 



On the other hand, to suppose either that 

 actual stars fall or leap across the sky, or that 

 some portion of them is taken away or pared off, 



