In most of the more lively fields of physical enquiry in the first three decades of the seventeenth century, a striking contrast may be observed between the antiquity of the problems attacked, and the innovatory procedures applied to solve them. None of these questions, inherited from a past now remote, seemed more pressing than the time-honoured controversy of the plenum versus the vacuum, especially as the concept of the atomic structure of matter was so closely associated with the existence of (...) the void. The more one studies the arguments produced at that time, the more one will be impressed with the value and importance, for the vacuists and the atomists, of the Pneumatics of Hero of Alexandria. When we read Galileo's explanation of combustion, “the extremely fine particles of fire, penetrating the narrow pores of the metal would fill the minute intervening vacuum, and would set free these minute particles from the forced attraction which these same vacua exert’, we can hear clear echoes of Hero's account of disseminated micro-vacua. Now Hero's work is clearly divided into two sections: a theoretical preface and a collection of 78 “pneumatic devices”. One might be tempted to claim that he, rather than his fellow-atomist Lucretius, inspired the first tentative syntheses of seventeenth-century atomism but it would still be necessary to agree that his chief contributions to the achievements of that generation lie in the experimental techniques which they derived from his instrumentation. Were it not for the popularity of his pneumatic demonstrations, he could never have won such a great reputation as a natural philosopher. Without that reputation, his opinions on this topic would not have been valued as almost equal to those of the mighty Aristotle, especially since he was so decidedly in the minority. (shrink)