<p>Torricelli, the inventor of the Mercury Barometer (~1644) argued that the height of the column of mercury was governed by atmospheric pressure (the "weight of the atmosphere" as he would have put it).   He asserted that the space above the mercury in his tube was a vacuum, a totally anti-Aristotlean concept at that time.<br>
To test this he enlisted the help of Blaise Pascal and Florin Perier in carrying one of two barometers up a mountain, the Puy de Dome in central France. His prediction was that the pressure at the top of the mountain would be less than at the base because of a lesser weight of air.<br>
The experiment showed a drop in height (ie of pressure) and Torriceli himself concluded that the height of the atmosphere would be about 20km, above which there would be vacuum - the same vacuum as in the top of the barometer tube. 
The experiment was IMHO one of the greatest experiments in the  history of physics.  See for example  <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768090/" rel="noreferrer">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768090/</a></p>

CC BY-SA 4.0
2019-03-14T15:04:26.677Z
2019-03-14T15:04:26.677Z
JonesTheAstronomer
<p><strong>I would argue the famous <a href="https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment" rel="noreferrer">Michelson-Morley experiment</a>.</strong></p>

<h2>Luminiferous Aether</h2>

<p>A bit of background first before getting into the experiment itself. It is quite easy to surmise, via Newton's laws of motion, that Earth should be in a vacuum, otherwise the constant drag of traveling through some medium must eventually cause us to crash into the Sun. Despite this Isaac Newton himself proposed the concept of a <a href="https://en.wikipedia.org/wiki/Luminiferous_aether" rel="noreferrer">Luminiferous Aether</a> which pervaded all of space and was the medium through which light propagated. Before this point there were various concepts of an "Aether" pervading space, but this, I believe, was the first truly scientific approach to the concept as a way of explaining physical phenomenon rather than a simple supposition of existence (such as the Greeks had done). The Luminiferous Aether was proposed as an almost magical concept to avoid numerous physical issues. I think Wikipedia describes it best.</p>

<blockquote>
  <p>The mechanical qualities of the aether had become more and more magical: it had to be a fluid in order to fill space, but one that was millions of times more rigid than steel in order to support the high frequencies of light waves. It also had to be massless and without viscosity, otherwise it would visibly affect the orbits of planets. Additionally it appeared it had to be completely transparent, non-dispersive, incompressible, and continuous at a very small scale.</p>
</blockquote>

<p>The concept of the Luminiferous Aether was accepted on the authority of Newton and inability to explain the propogation of light otherwise.</p>

<h2>Michelson-Morley Experiment (1887)</h2>

<p>It wasn't until the Michelson-Morley Experiment that the Luminiferous Aether was seriously shot down. The goal of the Michelson-Morley Experiment was to find evidence of this Luminiferous Aether and the null result was very strong evidence that this Aether did not exist.</p>

<p>The experiment itself was set up to measure the speed of light through this Aether. The idea was that as the Earth moved through the Aether, it would cause a sort of "Aether wind" that would slow down the speed of light. Thus if one measured the speed of light in the direction of the wind and perpendicular to it, one should get different speeds. The Michelson-Morley experiment set up exactly this scenario and used increasingly accurate measurements to try and find this difference in speed. Ultimate no difference was found and the Aether was ruled out as a material which existed.</p>

<p>From that point onwards it was assumed that space was a vacuum, completely devoid of anything. Oddly enough, this assumption was so strong, that people didn't even really believe in the concept of the Solar Wind at first and were quite perplexed initially when they sent the first rockets into space with particle detectors that ended up detecting all sorts of charged particles in space. Regardless, I would say the Michelson-Morley experiment is the first time scientists had scientific evidence that space was a vacuum.</p>

CC BY-SA 4.0
2019-03-08T16:35:36.423Z
oh this is a really interesting angle, thanks!
uhoh
CC BY-SA 4.0
2019-06-16T03:10:54.727Z
but the M-M experiment was before Einstein, and the Lorentz contraction explains the null result -- so the Aether is no longer ruled out by M-M.
amI
CC BY-SA 4.0
2019-03-08T16:31:19.533Z
2019-03-08T16:31:19.533Z
zephyr
<p>The question <a href="https://astronomy.stackexchange.com/q/29666/7982">Who was the first to realize that the Earth is surrounded by vacuum?</a> was closed because some users felt it was answered by answers to a different question in an different SE site: <a href="https://hsm.stackexchange.com/q/2389/3869">Who was the first to postulate that space was a vacuum?</a></p>

<p>To me the distance between <em>realize</em> and <em>postulate</em> is astronomical!</p>

<p>That aside, I've asked a new question: <em>What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?</em></p>

<p>By demonstrated I'm talking about a measurement that shows it is, or at least is likely to be the case that Earth is surrounded by vacuum. It should be something such that it could be presented as scientifically convincing evidence to other scientists of the time, unencumbered by non-scientific predispositions (e.g. religion, rivalry, philosophy...) </p>

CC BY-SA 4.0
2019-03-07T06:47:10.077Z
I'm voting to close this question as off-topic because this is a question more suited to the [History of Science and Mathematics SE](https://hsm.stackexchange.com/).
StephenG - Help Ukraine
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2019-03-07T06:49:49.017Z
@StephenG *more suited* is not a recognized reason to close a question. That's why it's not presented to you as an option. Unless you can show this is clearly off-topic, you should withdraw your close vote. OP decides where to ask, you don't vote to ask somewhere else. We have a `history` tag with 93 questions.
uhoh
CC BY-SA 4.0
2019-03-07T06:57:41.840Z
You're trying to ask the same question which was closed previously by rewording it and making a legalistic argument to justify it.  Nothing substantive has changed.  Resubmitting variations on the same question won't be well received by the community on Astronomy SE, IMO.  It's a history of science question and there's an SE for that - it's that simple.
StephenG - Help Ukraine
CC BY-SA 4.0
2019-03-07T07:01:36.920Z
@StephenG I think the last paragraph makes a clear argument why this is a different question, give it another read-through. In the mean time your close reason is not valid, the site has a long series of well-received questions about the history of astronomy.
uhoh
CC BY-SA 4.0
2019-03-07T07:05:18.270Z
No amount of repeated read thrus will change the fact that it's about the *history of science*.  Take the hint of the last questions close votes and comments.
StephenG - Help Ukraine
CC BY-SA 4.0
2019-03-07T07:08:33.267Z
@StephenG answers to [Are Questions related to Cosmology and ancient history of astronomy allowed in Astronomy SE?](https://astronomy.meta.stackexchange.com/q/363/7982) and [Do questions about the history and discoveries of astronomy belong here?](https://astronomy.meta.stackexchange.com/q/245/7982) and 93 questions tagged with `history` seem to argue in my favor here.
uhoh
CC BY-SA 4.0
2019-03-07T09:45:13.680Z
Is anyway surprising that a more or less clear answer cannot be found quickly.
Alchimista
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2019-03-07T10:26:11.173Z
@Alchimista refraction would be a dead giveaway...
uhoh
CC BY-SA 4.0
2019-03-07T10:40:24.253Z
@uhoh my English isn't enough to understand if refraction is suggested or won't be of much help.  Even an immense atmosphere could stratifies as to give refraction, like indeed our finite one does.
Alchimista
CC BY-SA 4.0
2019-03-07T11:15:48.603Z
@Alchimista it would be a giveaway that there was a drop in refractive index, but you are right, perhaps not necessarily that there was a vacuum out there. But a careful analysis near the horizon near sea-level combined with one on a high mountain might have been fairly convincing. Let's see how this goes.
uhoh
CC BY-SA 4.0
2019-03-07T18:10:23.370Z
You'd think Wikipedia would cover this: https://en.wikipedia.org/wiki/Vacuum But other a discussion of the aether which makes me think the discovery was 20th century, the info does not seem to be there.
Wayfaring Stranger
CC BY-SA 4.0
2019-03-08T07:53:31.153Z
I asked the now-closed question. HSM answers who proposed that vacuum exists above the atmosphere: Pascal [...] surmised existence of a vacuum above the atmosphere in 1648. Hooke presented an estimate of how far the atmosphere extends [...] (1665). It's still not clear who first stated this with certainty / confirmed this.
MrSparkly
CC BY-SA 4.0
2019-03-08T08:05:41.203Z
@MrSparkly thanks for the info, this is really interesting! In addition to *realize* and *postulate*, now we have a *surmised* ;-)
uhoh
<observational-astronomy><planetary-atmosphere><history><atmospheric-effects>
What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?
uhoh
# What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?

(Asked by: username_0 on 2019-03-07)

The question [Who was the first to realize that the Earth is surrounded by vacuum?](https://astronomy.stackexchange.com/q/29666/7982) was closed because some users felt it was answered by answers to a different question in an different SE site: [Who was the first to postulate that space was a vacuum?](https://hsm.stackexchange.com/q/2389/3869)

To me the distance between *realize* and *postulate* is astronomical!

That aside, I've asked a new question: *What was the first astronomical measurement which demonstrated that "the Earth is surrounded by vacuum"?*

By demonstrated I'm talking about a measurement that shows it is, or at least is likely to be the case that Earth is surrounded by vacuum. It should be something such that it could be presented as scientifically convincing evidence to other scientists of the time, unencumbered by non-scientific predispositions (e.g. religion, rivalry, philosophy...)

**Tags:** observational-astronomy, planetary-atmosphere, history, atmospheric-effects
> **Comments:**
> **username_1**: I'm voting to close this question as off-topic because this is a question more suited to the [History of Science and Mathematics SE](https://hsm.stackexchange.com/).  
> **username_0**: @StephenG *more suited* is not a recognized reason to close a question. That's why it's not presented to you as an option. Unless you can show this is clearly off-topic, you should withdraw your close vote. OP decides where to ask, you don't vote to ask somewhere else. We have a `history` tag with 93 questions.  
> **username_1**: You're trying to ask the same question which was closed previously by rewording it and making a legalistic argument to justify it.  Nothing substantive has changed.  Resubmitting variations on the same question won't be well received by the community on Astronomy SE, IMO.  It's a history of science question and there's an SE for that - it's that simple.  
> **username_0**: @StephenG I think the last paragraph makes a clear argument why this is a different question, give it another read-through. In the mean time your close reason is not valid, the site has a long series of well-received questions about the history of astronomy.  
> **username_1**: No amount of repeated read thrus will change the fact that it's about the *history of science*.  Take the hint of the last questions close votes and comments.  
> **username_0**: @StephenG answers to [Are Questions related to Cosmology and ancient history of astronomy allowed in Astronomy SE?](https://astronomy.meta.stackexchange.com/q/363/7982) and [Do questions about the history and discoveries of astronomy belong here?](https://astronomy.meta.stackexchange.com/q/245/7982) and 93 questions tagged with `history` seem to argue in my favor here.  
> **username_2**: Is anyway surprising that a more or less clear answer cannot be found quickly.  
> **username_0**: @Alchimista refraction would be a dead giveaway...  
> **username_2**: @uhoh my English isn't enough to understand if refraction is suggested or won't be of much help.  Even an immense atmosphere could stratifies as to give refraction, like indeed our finite one does.  
> **username_0**: @Alchimista it would be a giveaway that there was a drop in refractive index, but you are right, perhaps not necessarily that there was a vacuum out there. But a careful analysis near the horizon near sea-level combined with one on a high mountain might have been fairly convincing. Let's see how this goes.  
> **username_3**: You'd think Wikipedia would cover this: https://en.wikipedia.org/wiki/Vacuum But other a discussion of the aether which makes me think the discovery was 20th century, the info does not seem to be there.  
> **username_4**: I asked the now-closed question. HSM answers who proposed that vacuum exists above the atmosphere: Pascal [...] surmised existence of a vacuum above the atmosphere in 1648. Hooke presented an estimate of how far the atmosphere extends [...] (1665). It's still not clear who first stated this with certainty / confirmed this.  
> **username_0**: @MrSparkly thanks for the info, this is really interesting! In addition to *realize* and *postulate*, now we have a *surmised* ;-)  

---

## 2 answers

### Answer by username_5 on 2019-03-14. Score: 10

Torricelli, the inventor of the Mercury Barometer (~1644) argued that the height of the column of mercury was governed by atmospheric pressure (the "weight of the atmosphere" as he would have put it). He asserted that the space above the mercury in his tube was a vacuum, a totally anti-Aristotlean concept at that time.  
To test this he enlisted the help of Blaise Pascal and Florin Perier in carrying one of two barometers up a mountain, the Puy de Dome in central France. His prediction was that the pressure at the top of the mountain would be less than at the base because of a lesser weight of air.  
The experiment showed a drop in height (ie of pressure) and Torriceli himself concluded that the height of the atmosphere would be about 20km, above which there would be vacuum - the same vacuum as in the top of the barometer tube.
The experiment was IMHO one of the greatest experiments in the history of physics. See for example <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768090/>


---

### Answer by username_6 on 2019-03-08. Score: 5

**I would argue the famous [Michelson-Morley experiment](https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment).**

## Luminiferous Aether

A bit of background first before getting into the experiment itself. It is quite easy to surmise, via Newton's laws of motion, that Earth should be in a vacuum, otherwise the constant drag of traveling through some medium must eventually cause us to crash into the Sun. Despite this Isaac Newton himself proposed the concept of a [Luminiferous Aether](https://en.wikipedia.org/wiki/Luminiferous_aether) which pervaded all of space and was the medium through which light propagated. Before this point there were various concepts of an "Aether" pervading space, but this, I believe, was the first truly scientific approach to the concept as a way of explaining physical phenomenon rather than a simple supposition of existence (such as the Greeks had done). The Luminiferous Aether was proposed as an almost magical concept to avoid numerous physical issues. I think Wikipedia describes it best.

> The mechanical qualities of the aether had become more and more magical: it had to be a fluid in order to fill space, but one that was millions of times more rigid than steel in order to support the high frequencies of light waves. It also had to be massless and without viscosity, otherwise it would visibly affect the orbits of planets. Additionally it appeared it had to be completely transparent, non-dispersive, incompressible, and continuous at a very small scale.

The concept of the Luminiferous Aether was accepted on the authority of Newton and inability to explain the propogation of light otherwise.

## Michelson-Morley Experiment (1887)

It wasn't until the Michelson-Morley Experiment that the Luminiferous Aether was seriously shot down. The goal of the Michelson-Morley Experiment was to find evidence of this Luminiferous Aether and the null result was very strong evidence that this Aether did not exist.

The experiment itself was set up to measure the speed of light through this Aether. The idea was that as the Earth moved through the Aether, it would cause a sort of "Aether wind" that would slow down the speed of light. Thus if one measured the speed of light in the direction of the wind and perpendicular to it, one should get different speeds. The Michelson-Morley experiment set up exactly this scenario and used increasingly accurate measurements to try and find this difference in speed. Ultimate no difference was found and the Aether was ruled out as a material which existed.

From that point onwards it was assumed that space was a vacuum, completely devoid of anything. Oddly enough, this assumption was so strong, that people didn't even really believe in the concept of the Solar Wind at first and were quite perplexed initially when they sent the first rockets into space with particle detectors that ended up detecting all sorts of charged particles in space. Regardless, I would say the Michelson-Morley experiment is the first time scientists had scientific evidence that space was a vacuum.

> **Comments:**
> **username_0**: oh this is a really interesting angle, thanks!  
> **username_7**: but the M-M experiment was before Einstein, and the Lorentz contraction explains the null result -- so the Aether is no longer ruled out by M-M.  

---

