DECLINE OF ALEXANDRIAN SCIENCE 123 



Stoic philosophy, which was attended with a reversion to primitive 

 cosmical notions. Even in Hipparchus a somewhat critical atti- 

 tude, excellent in its immediate results, has been regarded by some 

 as foreshadowing the period of decadence which actually followed. 

 Astronomy is to remain nearly stationary for sixteen centuries. 



INVENTIONS. CTESIBTJS AND HERO. In the period of civil 

 war following the death of Alexander and followed in turn by 

 Roman conquest, much attention was naturally devoted to the 

 invention and improvements of military engines. Compressed 

 air came into use as a motive power and the foundations of 

 pneumatics were laid. 



Ctesibus, a barber of Alexandria, distinguished by his mechanical 

 inventions, and his follower Hero (or Heron) who flourished in the 

 latter part of the second century B.C., made notable inventions 

 and some real contributions to mathematical science. The works 

 attributed to Hero, on the basis of a great quantity of confused 

 and doubtful material, include : a Mechanics, treating of centres 

 of gravity and of the lever, wedge, screw, pulley, and wheel and 

 axle; various works on military engines and mechanical toys, a 

 Pneumatics the oldest work extant on the properties of air 

 and vapor describing many machines, among others a fire-en- 

 gine, a water-clock, organs, and in particular a steam-engine which 

 we may regard as a remote precursor of our modern steam turbine. 

 Many of the machines depend for their action on the flow of water 

 into a vacuum, which Hero, having no conception of atmospheric 

 pressure, attributed to nature's "abhorrence" of a vacuum. 

 He arrived at the important law for the lever and the pulley : 

 "The ratio of the times is equal to the inverse ratio of the forces 

 applied." The Dioptra, a treatise on a kind of rudimentary theod- 

 olite, discusses such engineering problems as finding differences 

 of level, cutting a tunnel through a hill, sinking a vertical shaft to 

 meet a horizontal tunnel, measuring a field without entering it, etc. 

 The instrument employed is described as a straight plank, 8 or 9 

 feet long, mounted on a stand but capable of turning through a 

 semicircle. It was adjusted by screws, turning cog-wheels. 

 There was an eye-piece at each end and a water level at the side. 



