180 SCIENCE IN GRECO-ROMAN ANTIQUITY 



pulley (Aulus Gellius, X, 12). However, it was 

 especially engines of war which appeared at the court 

 of Dionysius the Elder towards the year 400 B.C., to 

 be developed a century and a half later by the genius 

 of Archimedes. 



Besides powerful cross-bows and formidable catapults 

 stretched by means of a windlass, the Greeks had even 

 conceived the idea of the machine-gun : an ingenious 

 mechanism made balls of metal slide automatically in 

 the groove of a cross-bow each time it was drawn. 1 



The works of Hero show us also that the Greeks 

 already knew how to utilize currents of hot air, and 

 compressed air, and that they were on the way to 

 discover the motive power of steam, as is shown by 

 the seolipile. This apparatus is composed of a hollow 

 sphere pivoted horizontally, which is supplied with 

 steam from a boiler through one of the pipes serving 

 as a pivot. This steam escapes from the sphere in 

 opposite directions by two pipes situated at the 

 opposite ends of a diameter perpendicular to the axis 

 of rotation. By this arrangement the escape of the 

 steam causes the sphere to revolve with increasing 

 rapidity (Hero, I Pnenmatica, p. 230). In these works 

 there is a description of a lift and force pump for use 

 in case of fire (Hero, I Pneutnatica, p. 133), and also 

 the description of a hodometer similar in all points 

 to our taximeter. A small pin is fixed to the hub of 

 the carriage wheel, at each turn it moves a horizontal 

 wheel with spaced teeth. An ingenious system of 

 toothed wheels and endless screws transmits the move- 

 ment and turns the hands of the meters which mark 

 units of different magnitudes (Hero, III, Rationes 

 dimetiendi, p. 292). 



The construction of the automata employed in the 

 temples and theatres likewise reveals an intelligent use 

 of the physical forces then known. A mechanism 



1 10 Diels, Antike, p. 93. 



