A HISTORY OF SCIENCE 



qualifies his narrative by asserting that " persons who 

 are present attest the truth of the transaction when 

 there is nothing to be gained by falsehood." Nor 

 must we overlook the fact that a similar belief in the 

 power of royalty has persisted almost to our own 

 day. But no such savor of scepticism attaches to a 

 narrative which Dion Cassius gives us of an incident 

 in the life of Marcus Aurelius an incident that has 

 become famous as the episode of The Thundering 

 Legion. Xiphilinus has preserved the account of 

 Dion, adding certain picturesque interpretations of 

 his own. The original narrative, as cited, asserts that 

 during one of the northern campaigns of Marcus 

 Aurelius, the emperor and his army were surrounded 

 by the hostile Quadi, who had every advantage of 

 position and who presently ceased hostilities in the 

 hope that heat and thirst would deliver their ad- 

 versaries into their hands without the trouble of 

 further righting. "Now," says Dion, "while the 

 Romans, unable either to combat or to retreat, and 

 reduced to the last extremity by wounds, fatigue, heat, 

 and thirst, were standing helplessly at their posts, 

 clouds suddenly gathered in great number and rain 

 descended in floods certainly not without divine in- 

 tervention, since the Egyptian Maege Arnulphis, who 

 was with Marcus Antoninus, is said to have invoked 

 several genii by the aerial mercury by enchantment, 

 and thus through them had brought down rain." 



Here, it will be observed, a supernatural explanation 

 is given of a natural phenomenon. But the narrator 

 does not stop with this. If we are to accept the 

 account of Xiphilinus, Dion brings forward some 



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