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Lessons from the invention of the thermometer
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In last week’s post on the origins of the steam engine, I noted the importance of the inverted flask experiment, versions of which had existed since at least the third century BC. By the 1610s this ancient experiment had been reinterpreted as a device capable of measuring temperature.
It’s worth a quick refresher: the ancient experiment was simply to heat the base of a long-necked glass flask and place it mouth-first into a bucket of water. The heated air trapped inside the flask would bubble out, and as the remaining air cooled, the water of the bucket would rise up into the flask.
The experiment was then reinterpreted as a device for measuring temperature essentially by just adding a scale from which to read the level of the water as the air trapped inside the flask expanded with heat or contracted with cold. The invention of the thermometer was thus a shockingly simple and marginal improvement.
But who was responsible for the breakthrough? And why does it matter?
I last week credited Santorio Santorio, a professor of medicine at Padua, who in 1612 published a book on Galenic medicine in which he mentioned applying the inverted flask experiment to measuring temperature. But I also noted that his priority was disputed. I didn’t have the space to go into it then, but the story is a very interesting one and reveals some important truths about the process of invention.
The key problem for historians is that once everyone started talking about Santorio’s device, all sorts of people immediately rushed forward to claim it as their own. Or else to dismiss any notion that it was even new by pointing to how old the inverted flask experiment was.As is the nature of many breakthroughs, it was just so obvious that nobody could fathom how it could have been missed for so long. Many didn’t want to admit it. Santorio would in 1630 even concede, probably in response to someone questioning his originality, that it was indeed similar in form to the ancient device found in the works of Hero of Alexandria. But he held firm to his claim to innovation, which was in how to apply it.
What does the evidence tell us? The earliest known record of applying a gradated scale to the inverted flask experiment comes from a manuscript dated 1611 — a list of scientific marvels compiled by one Bartolomeo Telioux in Rome. He labeled it a method to “know the changes in weather in hot or cold in degrees or minutes”, and even provided a detailed drawing. Yet Telioux’s description seems to have totally misunderstood the device — it is back-to-front.So it’s unlikely that he was the inventor. Had he seen Santorio’s device?
It’s certainly possible. In the summer of 1612 the famous Galileo Galilei received a letter from a Venetian gentleman named Gianfrancesco Sagredo, which described Santorio’s instrument having heard of it from a friend who had seen it in Padua. Given the device was so simple — just a glass flask, a bowl, some water, and an inked scale — Sagredo had immediately replicated it and improved upon it further. Over the following years he even used it to measure changes in the weather from year to year.So clearly the news of the invention had travelled very quickly, and perhaps Telioux had even heard of the invention third-hand, by seeing a copy made by someone else entirely.
We may never know for sure, but Galileo’s response to Sagredo is what has complicated matters — he claimed the invention as his own! We don’t have Galileo’s actual responses, but by early 1615 Sagredo was noting in his replies that “as you write to me, and as I certainly believe, you were the first author and inventor”. Sagredo by then even referred to Santorio dismissively, as merely “the person who claims himself the inventor of these instruments”, even deriding him for a lack of understanding of how it worked.Many decades later, more of Galileo’s disciples would also credit the invention of the thermometer to their old master, placing it to c.1592-1603.
So was Galileo the true inventor? Frankly, I find it highly unlikely. Both Galileo and his disciples had a habit of exaggerating his achievements, and I think this is one of those cases. Galileo, like many others, certainly was aware of the inverted flask experiment. The letters he received in 1612 seem to suggest as much, and there is even a letter from the 1620s by Galileo himself, in which he claims he had played around with this “trick” when at Padua c.1606.But if Galileo did come up with the idea of using it to measure temperature, then he almost certainly failed to appreciate its potential, as his still calling the original experiment a “trick” suggests. Regardless, even if Galileo did realise its potential, he doesn’t seem to have communicated it. After all, even Sagredo — one of Galileo’s close friends and a former student — first heard of the thermometer as being Santorio’s. Ultimately, it was the far less famous Santorio who still managed to cause all the excitement.
But there’s one more complication to the story. In the same year as the publication of Santorio’s book and of Sagredo’s letter, Galileo received yet another letter — this time from one Daniello Antonini in Brussels. Antonini had seen a drawing of Cornelis Drebbel’s perpetual motion device, which featured so prominently in my series on the steam engine. Because Antonini was familiar with the inverted flask experiment, he correctly deduced that Drebbel’s device was powered by the heating and cooling of the air trapped inside the tube (though not realising, very understandably for the time, that it would also have moved thanks to changes in atmospheric pressure). Antonini then made a linear, simplified model of his own, and presented it to Albert of Austria, the sovereign of the Hapsburg Netherlands (modern-day Belgium).
Most strikingly of all, Antonini marked his simplified model with “equally distant thick lines and their numbers in such a way that it is possible to make notes of the motion”.It sounds like Antonini independently invented a Santorio-like thermometer, and at around the same time.
But not quite. Although he noted that the cause of the motion was from hot and cold, he didn’t say he used his markings to actually measure anything — they were seemingly just to better discern the movement of the liquid. Antonini even said he only made the model “on a whim”. Having made his demonstration, he then apparently troubled himself with also trying to copy Drebbel’s application of the rise and fall of the liquid to clockwork.
Santorio’s claim, it seems, is safe. But in this lies an important lesson for all would-be inventors. The inverted flask experiment had been around for centuries, and even been understood since ancient times as being caused by hot and cold. So its application as a thermometer was extremely low-hanging fruit. The likelihood of it being interpreted as a temperature-measuring device might have increased somewhat in the mid-sixteenth century, when we find the first mentions of it being done using a glass flask rather than an opaque metal container. Yet even then, the visible rise and fall of the liquid in the open bucket, rather than the flask, could always have been noted and measured against a scale in much the same way. What Antonini’s letter also shows us is that even when a scale was applied to the experiment, an ingenious person who knew their cutting-edge science like he did could still fail to appreciate the potential of what they had done.
But Santorio was different. Santorio had spent most of his career totally obsessed with measuring things in the name of medicine, and his thermometer was actually among the last of his inventions in this vein. He had already been a pioneer of the hand-held pendulum, or pulsilogium, to keep track of the human heart rate. He had already developed hygrometers to measure the humidity of the air. He had already developed devices to measure the intensity of both air and water flows. He had even already developed a special weighing chair, so that he could keep track of changes to bodyweight from eating, drinking, and excreting, and thus work out how much he and his patients would lose from unnoticed sweating.
What made Santorio so different, then, is that he became aware of the inverted flask experiment while already looking for measuring devices. He was already thoroughly primed for making the connection to measuring temperature. It’s the reality behind all those legendary Eureka! moments. It’s not that an ordinary person sees something mundane, like a cart’s wheel spinning when overturned (a legend about Hargreaves’s spinning jenny), or the steam from a kettle rising (a legend about Watt’s steam engine improvements), and an invention then springs fully formed into their mind. Instead, it’s that people who are already actively trying to solve particular problems become reminded or aware of potential solutions. The inverted flask experiment was ancient and common. A mind actively searching for ways to measure things was not.
Those who see room for improvement where others do not — those with the improving mentality — are the people open to this kind of inspiration. Yet even if you have lots of people with the improving mentality, any particular improvement still requires someone looking for solutions to a very specific problem. Which is why such low-hanging fruit as the invention of the thermometer can take so very long to be plucked. Inventors are rare enough to begin with— certainly historically, and even today when there are more inventors alive than ever before — but each breakthrough requires at least one of these rare creatures to have chosen to work on a very specific problem, from among innumerable options. (It’s also why there are so many cases of near-simultaneous invention, because it just takes two people to identify and pluck the same often low-hanging problem at the same time.)
Given the sheer size of what we haven’t yet achieved, with each new invention itself being capable of further improvement and each new discovery of being applied in myriad ways, I think we can expect there to be many more low-hanging fruit still out there, waiting only for a Santorio of their own to but reach out and pluck.
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Like the English physician Robert Fludd: Luca Guariento, ‘From Monochord to Weather-Glass : Musica Speculativa and Its Development in Robert Fludd’s Philosophy’ (PhD thesis, University of Glasgow, 2015), pp.246-7.
W. E. Knowles Middleton, A History of the Thermometer and Its Use in Meteorology (Johns Hopkins Press, 1966), pp.13-14
Arianna Borrelli, ‘The Weatherglass And Its Observers In The Early Seventeenth Century’, in Philosophies of Technology: Francis Bacon and His Contemporaries, ed. Claus Zittel et al. (BRILL, 2008), pp.111-13
Middleton, p.7; slightly differently worded translation in Matteo Valleriani, Galileo Engineer, vol. 269, Boston Studies in the Philosophy and History of Science (Springer, 2010), p.242
Piero E. Ariotti, ‘An Overlooked Autograph Letter of Galileo on the Thermometer’, Annals of Science 31, no. 5 (1 September 1974), pp.457–62
See translation of Antonini’s letter in: Valleriani, pp.227-8
Fabrizio Bigotti and David Taylor, ‘The Pulsilogium Of Santorio: New Light On Technology And Measurement In Early Modern Medicine’, Societate Si Politica 11, no. 2 (2017), pp.55-114