296 PHYSICAL SCIENCE BK. vn 



describes a curve in its orbit. Whether other 

 comets had this circular orbit I cannot say. The 

 two in our own age at any rate had. Again, every 

 thing kindled by a temporary cause quickly gives 

 out. Thus torches gleam only while they flit across 

 the sky ; thus lightning has strength for just one 

 stroke ; thus so-called shooting and falling stars fly 



2 past, cutting through the air. No fires have any con 

 siderable duration unless their strength is inherent. I 

 mean the divine fires which the universe maintains 

 eternally, because they are its parts and works. 

 These, I say, are always active ; they have an orbit 

 the even tenor of which they preserve, and they are 

 uniform. They would on alternate days be larger 

 or smaller if the fire was merely casual, the sudden 

 outcome of some accidental cause. Such a fire 

 would be greater or less according as it was fed 

 more abundantly or more scantily. I said a 

 moment ago that no fire could be lasting which 



3 arose from some defect in the atmosphere. I have 

 now to add further, that it can by no means be fixed 

 and steady. Both torch and lightning and shooting 

 star, and any other kind of fire forced out of the air 

 by pressure, are in flight ; none of them is visible 

 save in the course of its fall. But a comet has its 

 own settled position. For that reason it is not 

 expelled in haste, but steadily traverses its course ; 

 it is not snuffed out, but takes its departure. If it 

 were a wandering star (i.e. planet), says some one, it 

 would be in the zodiac. Who, say I, ever thinks 

 of placing a single bound to the stars ? or of cooping 



4 up the divine into narrow space ? These very 

 stars, which you suppose to be the only ones that 

 move, have, as every one knows, orbits differing 

 one from another. Why, then, should there not be 



