12 PHYSICAL SCIENCE BK. i 



falling. Otherwise the fires would flit about without 

 settling. When Gylippus was on the voyage to 

 Syracuse, a star appeared, resting on the very tip 

 of his lance. In the camp of the Romans at times 

 pikes appeared to be on fire, no doubt because fires 

 of this kind glided down on to them : these fires are 



*3 often wont to strike animals and trees, just like 

 thunderbolts. If, however, they are discharged 

 with less force, they merely glide down and settle, 

 and do not inflict stroke or wound. Again, some 

 are forced out from among clouds, others come from 

 a clear sky, if the atmosphere has got into a condi 

 tion to emit fire. In like manner, it occasionally 

 thunders with a clear sky, and from the same cause 

 as with a cloudy one, the atmosphere undergoing 

 internal collision. Even when the air is compara 

 tively clear and dry, it may become condensed, and 

 form bodies similar to clouds, the clashing of which 



14 causes the sound of the thunder. From time to 

 time, therefore, arise meteors like beams and like 

 shields, and the semblance of vast fires over the 

 sky, if a force similar in kind but greater in degree 

 encounter suitable material. 



II 



LET us now see how the brightness is produced 

 that sometimes envelops the heavenly bodies. 

 History has put on record that, on the day of the 

 late Emperor Augustus entrance into Rome on 

 his return from Apollonia, a parti -coloured circle, 

 such as is wont to be seen in a rainbow, appeared 

 round the sun. The Greeks call this a Halo ; 

 our most appropriate name for it is a Crown. 



