Un’”esperienza gentile” : fumo nel vuoto e leggerezza positiva all’Accademia del Cimento

In June of the year 1660 the members of the Accademia del Cimento conducted an experiment to study the behavior of smoke in a vacuum. This was just one of the many investigations carried out between 1657 and 1667 by the group of scholars gathered in Florence under the patronage of the Medici family. Paradoxically the experiment appeared to be a success, but this was only because they did not manage to create a perfect vacuum. In fact, in the absence of air and hence of oxygen the combustible material placed inside the Torricellian tube would never have ignited. This experiment had originally been conceived by Descartes in 1647 to furnish proof for his own conviction that a vacuum was impossible, but was used by the academicians in Florence to controvert the scholastic notion of levitas absoluta (absolute lightness) and the impossibility of the vacuum. To settle this matter, science would have to await Robert Boyle's demonstration that air was necessary for combustion, in which the failure of a candle to light in an airless environment was used by him to show the existence of the vacuum. These proposed and actual experiments with the vacuum - carried out under different conditions, based on different theories or hypotheses, and with very different outcomes - are significant because of the considerable amount of documentation that accompanied them, particularly with regard to the work by the Accademia del Cimento in Florence.