Huygens decided to repeat the experiment, but now with water purged of air by letting it stand in the receiver for a whole night. As our air-pump is clearly not as good as Huygens’s was, and leaks too much to keep it empty for a whole night, we purged our water by cooking it for a while. Just like Huygens, we replicated the void-in-the-void experiment with the purged water, and our observations match his: “Het experiment van den 21 Dec. gerepeteert, ende met verwonderingh bevonden, dat als ick het glas A opgevolt hadde met water dat van lucht gesuijvert was, soo wilde het selve niet weder neersacken, hoewel ick de lucht soo nae als mogelijck uijt gepompt hadde. [Replicated the experiment of the 21th of December, and found with surprise that if I filled the flask A with water purged of air, it didn’t fall down, even if I had pumped out the air as much as possible.]”
Normally, when the air was pumped out of the receiver, the water in the flask would sink down to the level of the water in the glass, just like we saw before. ‘Normally’, that is: in the Torricellian experiment as performed by Torricelli and as re-enacted by Boyle and by Huygens himself in the previous chapter. The fact that Huygens had purged the water of air should not make a difference: if the water in the flask falls down because the pressure on the water in the glass is released, then it shouldn’t matter whether there’s air in the water or not. But if it is indeed the pressure of the air on the water in the glass that keeps the water in the flask up, and if the receiver was truly empty of air, then what was it that held the column of water suspended?
Huygens called this failure of the water to fall ‘anomalous suspension’. He then introduced a small bubble of air into the flask, started pumping and noticed how the water again subsided. So the Torricellian experiment apparently only gave the expected outcome when the water in the flask contained some quantity of air. He wrote: “Dit most men vorder ondersoecken met langer pijpen van 2 à 3 voet. Het schijnt hier uijt dat de lucht wel hondert duijsend mael en meer sich uijtreckt, ende dan noch gewelt doet met sijn veerachtighe kracht, ofte daer moet behalven het gewight en de Elater van de lucht noch iets anders daer in te considereren sijn, tot noch toe onbekent. [This has to be investigated further with longer pipes of 2 to 3 feet. This seems to show that the air expands a hundred thousand times and more, and even then pushes with its spring, or else besides the weight and spring of the air something else must be considered, as yet unknown.]”
Huygens reported his results to the experimental communities in Paris and London, but no one was able to replicate the anomaly, so at first he was not believed. The first strategy used by the experimental community to deal with this indecision was therefore to not accept the produced phenomenon as a matter of fact. Boyle, for instance, argued that the anomaly was simply a sign of the incapacity of Huygens’s pump.
But when in 1663, Huygens visited London and helped to build an air-pump, the anomalous suspension was finally reproduced and accepted as a matter of fact. It turned out that Boyle’s incapacity to reproduce the phenomenon was a sign of the incapacity of his pump. Whether an accepted matter of fact could prove the (in)capacity of one’s pump, or rather the capacity of one’s pump could establish a matter of fact, was a question for ever at stake.
Even though the anomalous suspension was accepted as a matter of fact, it stayed ‘anomalous’: there was no generally accepted explanation for it. Many experimental philosophers studied the problem, but it remained unsolved for several years. So not only the column of water, but the whole experimental community was now held up in suspension, as there was a matter of fact that did not immediately and unambiguously tell something about the world outside the laboratory. In order to give it meaning, something that was kept out needed to be brought back in: Huygens argued that not only the pressure of the surrounding air was responsible for the suspension of the column of water, but also the presence of a subtle matter. This subtle matter was able to penetrate everything and only became active in the total absence of air, when the water was purged of air. Huygens also argued that the spring and pressure of the air was due to the motion of this subtle matter. And as the subtle matter could penetrate anything and was present everywhere and could therefore by no means be locked up in a laboratory, Huygens had not only come to refute the same hypothesis as he was trying to prove (the possibility of a void), but had also introduced an entity that he didn’t know how to experimentally test. It could, therefore, not be established as a matter of fact, and remained a matter of speculation.
Probably without intending to do so, Huygens had taken the matter of fact out of its comfort zone, exposing it to the dangers of speculation. In that way, he revealed that the laboratorium of the experimental philosophers could not be sealed tight against metaphysics, and that experimental matters of fact and theoretical speculations are inseparably interwoven. Or, to echo Boyle’s worst fear: “The air-pump leaks!”