From Vitruvius’s allusions to the works of Ctesibius and from a survey of those works current under Hero’s name which are chiefly concerned with mechanical contrivances and devices, the modern reader gets the impression that, aside from military engines and lifting appliances, the science of antiquity was applied largely to purposes of entertainment rather than practical usefulness. However, in Hero’s case at least there is something more than this. His apparatus and experiments are not intended so much to divert as to deceive the spectator, and not so much to amuse as to astound him. The mechanism is usually concealed; the cause acts indirectly, intermediately, or from a distance to produce an apparently marvelous result. It is a case of thaumaturgy, as Hero himself says,[892] of apparent magic. In fine, the experimental and applied scientist is largely interested in vying with the feats of the magicians or supplying the temples and altars of religion with pseudo-miracles. [Sidenote: Instances of experimental proof.] The introduction or proemium to the _Pneumatics_ is rather more truly scientific and has been called an unusual instance in antiquity of the use as proof of purposive observation of nature and experiment. Thus the existence of air is demonstrated by the experiment of pressing an inverted vessel, kept carefully upright, into water, which will not enter the vessel because of the resistance offered by the air already within the vessel. Or the elasticity of air and the existence of empty spaces between its particles is shown by the experiment of blowing more air into a globe through a siphon, and then holding one’s finger over the orifice. As soon as the finger is removed the surplus air rushes out with a loud report. Along with such admirable experimental proof, however, the introduction contains some astonishingly erroneous assertions, such as that “slime and mud are transformations of water into earth,” and that air released from a vessel under water “is transformed so as to become water.” Hero believes that heat and light rays are particles of matter which penetrate the interstices between the particles composing air and water. [Sidenote: Magic jugs and drinking animals.]