ALEXANDRIAN OR HELLENISTIC PERIOD 



duced by the expulsion of air through tiny tubes pass- 

 ing up through their throats from a tank below. The 

 owl is made to turn by a mechanism similar to that 

 which manipulates the temple doors. The pressure is 

 supplied merely by a stream of running water, and the 

 periodical silence of the birds is due to the fact that this 

 pressure is relieved through the automatic siphoning 

 off of the water when it reaches a certain height. The 

 action of the siphon, it may be added, is correctly ex- 

 plained by Hero as due to the greater weight of the 

 water in the longer arm of the bent tube. As before 

 mentioned, the siphon is repeatedly used in these 

 mechanisms of Hero. The diagram will make clear 

 the exact application of it in the present most ingenious 

 mechanism. We may add that the principle of the 

 whistle was a favorite one of Hero. By the aid of a 

 similar mechanism he brought about the blowing of 

 trumpets when the temple doors were opened, a phe- 

 nomenon which must greatly have enhanced the mysti- 

 fication. It is possible that this principle was util- 

 ized also in connection with statues to produce seem- 

 ingly supernatural effects. This may be the explana- 

 tion of the tradition of the speaking statue in the tem- 

 ple of Ammon at Thebes. 



The utilization of the properties of compressed air 

 was not confined, however, exclusively to mere toys, 

 or to produce miraculous effects. The same principle 

 was applied to a practical fire-engine, worked by levers 

 and force-pumps; an apparatus, in short, altogether 

 similar to that still in use in rural districts. A slightly 

 different application of the motive power of expanding 

 air is furnished in a very curious toy called "the dan- 



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