 Gasparo Berti's experiment. |
The experiment on
"quicksilver", carried out in Spring 1644, made Torricelli's name famous in
Italy and transalpine Europe. The Italian scientists merit was, above all, to admit that
the effective cause of the resistance presented by nature to the creation of a vacuum was
probably due to the weight of air. This opinion, as it is known, was not shared by
Galileo. The Florentine experiment was thus initially motivated by a desire to determine a
possible relationship between the weight of the air and the resistence which encountered
when attempting to produce a vacuum. A similar experiment had already been carried out in
Rome, probably when Galileo was still alive, by Gasparo Berti, in the presence of the
Jesuit fathers Niccol˜ Zucchi and Athanasius Kircher, but the results were only
divulged in 1647. Berti had used water, so the tube had a length of around ten meters.
Torricelli's original idea, and his technical contribution to the experiment, consisted in
using mercury instead of water, an innovation which allowed the length of the tube to be
reduced by a factor of thirteen. Even before carrying out the experiment, Torricelli asked
himself if the column of mercury would leave an empty space behind when it descended to a
position of equilibrium with the column of stmospheric air outside the tube. Torricelli's
experiment provoked enormous interest, particularly in France and Poland. The discussions
were not always focussed on the technical aspects of the experiment, or the scientific
conclusions which it was possible to draw from it, but instead raised yet again the
polemic between "ancients" and "moderns". The partial drop of the
level of the mercury in the tube produced an apparently empty space at the top of the
tube, placing one of the basic principles of Aristotelian physics in jeopardy. The Jesuits
fought with conviction to defend the impossibility of the vacuum. One might reasonably
wonder about the extent of Torricelli's engagement with the debate. The answer is simple:
he did not participate at all. In two letters addressed on the 11
and 28 June 1644 to Michelangelo Ricci, the mathematician of
the Grand Duke described the experiment, but took no position in the philosophical debate
raised by the apparent vacuum. He simply observed, in the letter of 11 June, that
"many have said that the vacuum does not exist, others that it can exist but only
with difficulty and against the repugnance of Nature". Additionally, Torricelli did
not consider the experiment to have succeeded because the height of the column of mercury
which had to balance the weight of the air was caused to vary "by the heat and the
cold". In any case, one can reach the conclusion that the value of the weight of the
air proposed by the "ancients" was completely erroneous. Another very important
result was that the force that prevented the mercury from falling was not inside the tube;
Torricelli, in the same letter, proposed the hypothesis that this force was external, and
was due to the "heaviness of the air". The two letters to Ricci are the only
documents written by Torricelli himself on the subject. It might be hypothesized that this
silence was due to his unhappiness at the intervention of theologians in the debate. A
phrase of Ricci's, in a letter sent to Torricelli on 18 June 1644,
provides some support for this hypothesis: "I estimate that you will unfortunately be
too nauseated by the temerarious opinion of these Theologians, and by their constant habit
of mixing up things of God with natural questions, where they should instead be treated
with greater respect and reverence" The motivations behind the participation in the
debate by eminent dignitaries of the Roman church are complex and still not fully
clarified at the present time. In any case, one can observe that for the defenders of the
Thomist-Aristotelian tradition, the existence of the vacuum, which was generally
associated with that of atoms, recalled the philosophy of Leucippus, Democritus and
Epicurus, whose followers were considered closer to heresy than to Catholic orthodoxy on
certain issues. It is not to be excluded that atomism was combatted because of the
difficulties which it would generate for a reliable interpretation of the "dogma of
transubstantiation".
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