[HN Gopher] In 1870, Lord Rayleigh used oil and water to calcula...
___________________________________________________________________
In 1870, Lord Rayleigh used oil and water to calculate the size of
molecules
Author : mailyk
Score : 535 points
Date : 2024-09-23 19:08 UTC (1 days ago)
(HTM) web link (www.atomsonly.news)
(TXT) w3m dump (www.atomsonly.news)
| hn_throwaway_99 wrote:
| I love articles like this. I feel like too often in science
| education (at least my science education) that laws and theories
| are presented as just something that you need to memorize, when
| in my opinion the stories of how things were originally
| discovered and figured out is eminently more fascinating and
| inspiring. Like I remember having to learn all of these
| biochemical pathways, but I left school with nary a clue as to
| how these pathways were uncovered in the first place.
|
| Thanks for submitting! Would welcome suggestions for any other
| publications on how scientific theories were first discovered.
| stevenwoo wrote:
| Did you get your physics education in high school or
| university? I only had to take one physics class in the USA at
| college for my major, quantum electrodynamics for electrical
| engineering but my professor wrote the textbook and I recall he
| went over each experiment starting from the fundamentals of our
| understanding of the basics of the atom, Newton's understanding
| of light at the time, double slit experiment, to Maxwell's
| equations, the Michelson Morley ether experiment, to deriving
| then proving experimentally proving general relativity and
| decomposing GR into Newtonian physics/other laws of
| electromagnetism, I am still in awe at the people just figuring
| this stuff out from first principles.
|
| Anyways, I haven't read this (have it on hold at my library)
| but someone recommended this book on reddit How to Make an
| Apple Pie from Scratch: In Search of the Recipe for Our
| Universe, from the Origins of Atoms to the Big Bang
| https://www.publishersweekly.com/9780385545655
| layer8 wrote:
| > experimentally proving general relativity
|
| Can you elaborate on that? What experiments did the professor
| perform?
| stevenwoo wrote:
| I mis wrote, he talked about the experiments done to verify
| general and special relativity. Michelson-Morley was one of
| them that sticks in my mind along with some traveling
| atomic clocks. We never recreated the experiments like some
| of the other commenters did in their classes.
| augustusseizure wrote:
| What's the name of that textbook? It sounds really
| interesting.
|
| Isaac Asimov wrote a couple books that follow the narrative
| of science from the beginnings up until the 80s or so, which
| I highly recommend. One is called Atom and is more focused on
| how we got to our "present" understanding of particles.
| There's also one that takes a broader view, it's something
| like History of Science (? not at my bookshelf right now).
|
| There's several books in this genre for math as well. IMO
| it's a much better structure for pedagogy since we can piggy
| back the education on our natural wiring to care about
| narrative and mystery/puzzles.
| ghastmaster wrote:
| You're referring to The History of Physics. An excellent
| read for a budding mind.
|
| Asimov was incredibly talented.
| owyn wrote:
| I was looking at my parent's bookshelf and saw a book on
| Shakespeare and I recognized the author's name: Asimov!
|
| https://en.wikipedia.org/wiki/Asimov's_Guide_to_Shakespea
| re
|
| It's like 800 pages, I haven't read it but I think I'll
| keep that one. Seems like it might be hard to find
| another physical copy. He was definitely prolific on a
| number of topics.
| lIl-IIIl wrote:
| Not surprising!
|
| "Asimov was so prolific and diverse in his writing that
| his books span all major categories of the Dewey Decimal
| Classification except for category 100, philosophy and
| psychology" - from his Wikipedia page.
| dotancohen wrote:
| He was also incredibly talented in phrasing ideas so that
| they stick in the reader's mind. I am right now sitting
| next to a dog Asimov named after him.
| hammock wrote:
| Understanding Physics? https://www.goodreads.com/book/sho
| w/41819.Understanding_Phys...
| lIl-IIIl wrote:
| His book "Understanding Physics" is amazing. Similar in
| spirit to Petzold's "Code" that is often praised on HN.
| albrewer wrote:
| There's a youtube channel called "Kathy Loves Physics &
| History"[0] that goes over all these things in video form.
|
| [0]: https://www.youtube.com/@Kathy_Loves_Physics
| bookofjoe wrote:
| Also, George Gamow's work is exemplary in making complex
| ideas understandable.
|
| See, for example:
|
| >One, Two, Three... Infinity: Facts and Speculations of
| Science (1947)
|
| https://www.amazon.com/One-Two-Three-Infinity-
| Speculations/d...
|
| PDF: https://archive.org/details/OneTwoThreeInfinity_158
|
| ..........................
|
| >Thirty Years that Shook Physics: The Story of Quantum
| Theory (1966)
|
| https://www.amazon.com/Thirty-Years-that-Shook-
| Physics/dp/04...
|
| PDF:
| https://archive.org/details/ThirtyYearsThatShookPhysics-
| TheB...
| ddfs123 wrote:
| That was my Physics too, but Chemistry just completely
| glanced over the history. Same thing with Mathematics, no
| backstory of mathematicians. I guess that either 1. Physics
| History is short enough, well-recorded, or 2. Physicists
| really like teaching their history.
| hn_throwaway_99 wrote:
| Yeah, in retrospect I think this aligns with my experience.
| But I'd even say that with the famous physics experiments I
| still remember often thinking "How did they get such
| precision with such primitive instruments?" I mean they
| would explain the experiments in very basic/schematic
| terms, but would have been nice to actually replicate I've
| to truly understand how it worked.
| SJC_Hacker wrote:
| Physicists seem to be always seeking a deeper understanding
| of everything, more so than other fields like biology and
| sometimes chemistry, who have a tendency to get bogged down
| into to the idiosyncrasies of particular phenomena.
| shepherdjerred wrote:
| MIT has an excellent chem course on YouTube that goes into
| the history
| DonaldFisk wrote:
| > to deriving then proving experimentally proving general
| relativity and decomposing GR into Newtonian physics/other
| laws of electromagnetism
|
| Do you mean Special Relativity, which covers classical
| mechanics and electromagnetism? General Relativity covers
| gravitation and cosmology without electromagnetism (though
| Kaluza and later Klein devised a theory unifying gravity and
| electromagnetism by adding an fifth dimension to General
| Relativity, which can then be decomposed into 4-dimensional
| GR and Maxwell's equations).
| knodi123 wrote:
| you only had to take one physics class, and it was quantum
| electrodynamics??? That sounds to me as if someone said "The
| only math class I've taken was differential equations."
| leafmeal wrote:
| I read Chasing the Molecule by John Buckingham recently and
| thoroughly enjoyed it! It give a good outline of the history of
| modern chemistry in a way that felt accessible but still
| thorough.
|
| It also does a great job of explaining the different characters
| and their stories. Some little-known who moved chemistry
| forwards in profound ways, and others, very well-known, who
| through their loyalty to false theories ended up holding it
| back.
|
| It's also a pretty short book when helps make it feel
| accessible.
| schrectacular wrote:
| As part of 9th grade biology we had to read "Microbe Hunters".
| The grades ahead insisted that it was awful and boring but I
| devoured the whole thing in a weekend. So thankful that it was
| part of the curriculum.
| NegativeLatency wrote:
| Discovering the quantization of the charge of electrons sounds
| like something you'd be interested in:
| https://en.wikipedia.org/wiki/Oil_drop_experiment
|
| We did it with several hundred volts (DC, scary) in college and
| it was pretty fun collecting the data and watching the numbers
| fall out in excel doing the analysis.
| physicsguy wrote:
| I remember doing this one and the equipment leaking oil all
| over me! Not long after that I decided to go more
| Theoretical...
| snatchpiesinger wrote:
| We also did it in uni, it was very exhausting. And after a
| full day of measurements noone ever had enough data to see
| the quantization of the charge of electrons.
| namuol wrote:
| So very true. The greatest science teachers understand the
| power that comes with the stories of scientific discovery.
|
| Carl Sagan's Cosmos and some of Richard Feynman's best lectures
| come to mind as some of the most memorable examples, but I'm
| certain all the best teachers out there know to incorporate the
| historical and human aspects to bring the essential perspective
| and natural mnemonic anchors to otherwise "dry" subjects.
| at_a_remove wrote:
| When I was a tutor, mostly doing math, when it came to
| polynomials and that range, I would trick my students into
| deriving the quadratic equation. It's not even a full page.
| Almost all of them finished with a strange expression, and then
| we had the little "it was always there, waiting for someone to
| find it" chat.
|
| Some people care about the history, some don't. I find when
| people talk about astrophysics stuff, most of them do not know
| the history and _ought_ to, because most of their
| interpretations fall into the "Yes, that was a question in the
| 1960s but eventually ..."
|
| If you want one for relativity, I strongly suggest _Was
| Einstein Right?_ by Clifford Will. It dates from 1986, so it is
| nearly forty years behind now, but it covers the many
| experiments and tests of relativities special and general.
| RheingoldRiver wrote:
| I highly recommend this book!
| https://www.goodreads.com/book/show/25238350-the-hunt-for-vu...
| jonny_eh wrote:
| I'd recommend this one instead: https://en.wikipedia.org/wiki
| /A_Short_History_of_Nearly_Ever...
| lern_too_spel wrote:
| How we derived the laws and theories _is_ science. (Some of the
| other commenters are mixing this together with biographies of
| the scientists, which is not science but is sometimes
| interesting in its own right.) The laws and theories in
| isolation are just trivia, and any class that teaches just
| those cannot truthfully be called a science class. Demand a
| better education.
| tsimionescu wrote:
| Both have their value, both the process and the results. And
| given the immensity of scientific knowledge, you can only
| learn so much of it in a K-12 education, or even in college.
|
| I don't think it's a priori wrong to teach students our
| current understanding of the world, without going into the
| details of how we came up with it. I also don't think it's
| wrong to add those details, but the more details you add, the
| less of the full picture you'll be able to present. And I
| definitely don't think it would be a good idea to teach
| children how we do science, without teaching them what we
| actually learned from doing it.
|
| I'd also say that the reality of _some_ of the process is
| extraordinarily boring ( "we kept meticulous records of
| precisely where on the sky various stars were each night, and
| how their position changed, for a few hundred years, and
| tried finding a function that matched those numbers; for a
| few hundred years, we kept adding more and more circles to
| correct things, until Kepler came up with some ellipses").
| And that for many children, learning history is already a
| huge bore, learning the history of science in addition would
| make science classes much worse. For others, the opposite is
| true.
| lupusreal wrote:
| Most of the general public would be better served with more
| emphasis on the history of science. Knowing how and when it
| happened makes it seem less like magic dogma given to them
| from the elders, against which rebellion is appealing.
| cchi_co wrote:
| The journey behind scientific discoveries for me is as
| captivating as the discoveries themselves
| danielam wrote:
| Yes, often what is taught is taught in a manner that seems
| mysterious in origin, as if it were revealed, certain and
| final, and developing a sensibility like that concerning
| scientific matters is not good. You could argue that the
| viability of science as such rests on certain articles of
| faith, but the particular findings of science themselves are a
| matter of demonstration, interpretation of demonstration and
| argument making use of interpreted demonstration, as well as
| the making of certain working assumptions that do quite a bit
| of quiet heavy lifting. The last, I think, receives too little
| attention, but it also supports the idea that practical and
| pragmatic rather than theoretical motives and habits drive much
| of scientific activity.
| nobrains wrote:
| Pragmatic or luck? Hear me out...
|
| Why assume "that the oil formed a single layer of molecules
| -- a monolayer" ?
|
| That is a very fundamental assumption, and could have been
| wrong as well (we know it is right, because the values match
| with more accurate recordings, but still...)
| hn_throwaway_99 wrote:
| Yes! Not to get too political, but I saw a lot of this during
| the Covid debates, e.g. "Trust the science!" Noooo! Science
| is not just something you're supposed to "trust", but
| something that's supposed to be supported by evidence.
|
| Yes, I definitely understand that most people don't have the
| training and background to understand complex scientific
| topics, and in some ways we do have to trust the scientific
| community if we're not a part of it. And I get frustrated by
| the common calls of "Do your own research!", which often
| means "Look at these YouTube grifters with absolutely no
| training who are just spouting stuff with no research of
| their own." But even the underlying problem with that is that
| most people aren't trained to evaluate the quality of data
| and motivations of people making it, and that is what
| scientific education _should_ be about. For example, I may
| have to "trust" the scientific community when it comes to
| data about infectiousness of COVID because I'm not an
| epidemiologist, but how that data is translated into rules
| and regulations is a policy call, and that policy call is not
| necessarily one where the epidemiologists are the experts. I
| shouldn't be told to "trust the science" as though I should
| just accept policy recommendations even if I do accept the
| underlying data about transmissibility.
| cb321 wrote:
| It isn't like "scientists" (whatever that means) don't also
| delegate to equipment or hardware manufacturers or
| (mathema|statis)ticians or compilers (or grad students,
| LOL). Sure they calibrate & cross-check, but while oil
| spread-out over water is easy to replicate at home in a few
| minutes with an oil dropper (maybe even with precocious
| (maybe pre-)pubescent kids not just Feynman Lectures on
| Physics Caltech Undergrads [1]), "more interesting/complex
| questions" usually have "full stacks" that are impractical
| to fully vet in general (see, e.g. Ken Thompson's
| _Reflections On Trusting Trust_). Epidemic disease coupled
| with human behavior is definitely getting into "holy crap
| complex" territory.
|
| In its barest essence the problem is this - delegation
| affords so much that it is basically unavoidable, but trust
| sure is tricky. The
| https://en.wikipedia.org/wiki/Demarcation_problem -
| searches for how to demarcate trustworthiness. Sorry to
| say, but there is a long history of failure to get
| consensus. It's notably a competitive game and as long as
| anything has been deemed valuable there have been cheap
| knock-offs (e.g. Fool's Gold), but things like The News you
| seem to complain of (e.g. Crichton's Gell-Mann Amnesia [2])
| or "conclusions", being more abstract than metal (often the
| metaphorically concrete), are trickier still to discern
| reliability.
|
| It may be the single _most central_ (in latitude-long 's of
| WHAAA? coordinates) problem of today's human condition /
| experience. I think it's a
| https://en.wikipedia.org/wiki/Wicked_problem BUT the
| problem applies recursively to advice from anyone about
| trust/delegation (or about anything else). So, _don 't
| trust me_. LOL. ;-) I don't think others can really answer
| these questions for someone. Part of life is learning to
| live with uncertainty, however precisely modeled. I'm just
| trying to share a perspective (and several relevant links!)
| on some of the principles involved with someone who seems
| interested in and frustrated by the questions.
|
| [1] https://physics.stackexchange.com/questions/244659/how-
| did-r...
|
| [2] https://en.wikipedia.org/wiki/Michael_Crichton#Gell-
| Mann_amn...
| wheatgreaser wrote:
| but chronological order of scientific discoveries does not
| imply conceptual linearity, so i kinda get why colleges and
| schools do not go for that kind of approach
| humansareok1 wrote:
| There's literally a dedicated major called History of Science.
| They teach fundamentally different things for different
| reasons.
| SkyBelow wrote:
| >that laws and theories are presented as just something that
| you need to memorize
|
| That's part of a larger problem in how science is presented. It
| is presented as something that is true, when it isn't. It is a
| model that describes reality. The models you are learning in
| high school and entry undergrad classes are mostly wrong models
| whose main use is that they are great building blocks to more
| complex models, as they work well enough in ideal conditions
| and correlate well enough with our exist. Yet even the best,
| most up to date models, aren't right. They work well enough in
| the places they are used that we can bet human lives on them,
| but that doesn't mean they describe what the universe is
| actually doing. Unless someone finds a way to crack open up the
| universe and check the "source code", we will never know
| exactly what the universe is doing and are limited to only ever
| improving models that approach the truth, like a sum that
| converges on a value at infinity but never equals that value
| for any finite sum of the series.
| iamflimflam1 wrote:
| Pretty sure I remember recreating this experiment in high
| school chemistry.
| andruby wrote:
| Same here (Belgium). We recreated a lot of experiments in
| class
|
| Even our math teacher would tell us the stories of how
| mathematicians "came" to their solutions.
|
| A good teacher makes such a huge difference
| nick238 wrote:
| The page is timing out for me, but is it the inverse problem of
| the time when Steve Mould/Matt Parker measured the unknown
| quantity p, but already assuming a size of the molecules?
| Presumably Lord Rayleigh already had a at least a good order-of-
| magnitude approximation of pi...
|
| https://www.youtube.com/watch?v=lmgCgzjlWO4
| thirdhaf wrote:
| By 1870 pi was known to several hundred decimal digits, for
| something like this calculation where you have other large
| sources of error Archimedes approximation from 2 millennia
| earlier would probably be fine. (<1% error)
|
| https://en.m.wikipedia.org/wiki/Chronology_of_computation_of...
| jjk166 wrote:
| Note that pi to 40 digits is sufficient to calculate the
| circumference of the observable universe to subatomic
| precision.
| bqmjjx0kac wrote:
| > Assuming that the oil formed a single layer of molecules -- a
| monolayer -- then the thickness of the oil film is the same thing
| as the length of one oil molecule.
|
| How did he know that the film of oil was one molecule thick?
|
| It feels like a huge assumption to me, but maybe this blog post
| left something out.
| munchler wrote:
| Agreed. The experiment actually gives an upper limit on the
| size of a molecule in one particular dimension. Still a very
| useful result.
| layer8 wrote:
| It isn't necessarily an upper bound. The molecules might
| spread out more distant than their size.
| bagels wrote:
| Wouldn't that provide an upper bound then? If the real size
| is equal to or less than the calculated size?
| gus_massa wrote:
| In a very unlucky world, they can form a 2D net, with
| molecules instead of strings and a lot of tiny holes.
|
| If this seams impossible, remember that when water freeze
| into ice, it expands to a 3D "net" with empty holes.
| happytoexplain wrote:
| It feels intuitive that a thin fluid on a low-friction surface
| (like water) would spread out "as much as possible" given
| enough time. There certainly may be confounding factors, but it
| seems like a reasonable thing to pin as an "assumption" in a
| hypothesis. I.e. he didn't have to "know" - assumptions are OK,
| and I don't feel like this one is _huge_.
| chmod775 wrote:
| > It feels intuitive that a thin fluid on a low-friction
| surface (like water) would spread out "as much as possible"
| given enough time.
|
| Most fluids _do not_ behave this way in most circumstances,
| because of surface tension, so it 's really not intuitive.
|
| This experiments is one of the few ways you _can_ get an
| accurate measurement. Many other fluids will either mix or
| end up as bubbles /blobs many orders of magnitude thicker
| than a molecule.
| komali2 wrote:
| I'm confused, the blog wrote "known amount of water," so was
| it a closed little area like a bathtub? If you added a ton of
| oil wouldn't it spread out as much as possible aka 600
| molecules thick or whatever?
|
| Or did he pour it into a huge lake or something?
| Cheer2171 wrote:
| One drop in a soup bowl sized petri dish, measure the area
| it covers.
| komali2 wrote:
| Surely the first thing to test would be dropping it in
| increasingly large soup bowls until there's obvious gaps?
| kqr wrote:
| How would the gaps be obvious? I'm not sure I could tell
| 1 molecule from 0 molecules when it comes to the
| thickness of oil film.
| MereInterest wrote:
| My understanding is that the actual body of water was
| larger, but that the oil would only spread out to one
| molecule of thickness. So you start with a larger area of
| water, and measure the diameter of the resulting oil slick.
| stolen_biscuit wrote:
| > How did he know that the film of oil was one molecule thick?
|
| He didn't. It was an assumption
| tech_ken wrote:
| Blog post seems to have elided this point, but it did link the
| original paper which was quite short:
| https://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/old_lite...
|
| Rayleigh's experiment was actually trying to solve for the
| minimum thickness of oil required to stop some camphor shavings
| from moving around on the water. He never states it explicitly,
| but I think the assumption is that the minimum thickness
| required to stop the shavings' movement would be such that the
| oil volume 'just' covers the surface, ie. is 1 molecule thick
| everywhere and hence the shavings never touch water. I think
| he's specifically making a slightly more clever point about
| surface tension, but that's a little beyond me.
| youainti wrote:
| Camphor would release compounds that adjust the surface
| tension of water. So the oil would break that direct
| relationship.
| tech_ken wrote:
| Ahhh that's cool, thanks for clarifying
| zokier wrote:
| Reading the paper, there is no mention of sizes of molecules.
| Did Rayleigh actually make the connection between film
| thickness and molecular size at some point? Or is that just
| modern retconning?
| tech_ken wrote:
| It's really ( _really_ ) quick but the first line of the
| second para is:
|
| > In view, however, of the great interest which attaches to
| the determination of molecular magnitudes, the matter
| seemed well worthy of investigation...
|
| So it seems like his main goal was to understand the size
| of molecules via his film-thickness measurements
| zokier wrote:
| Replying to myself, I found 1899 paper which is more
| explicit on the matter, and shows how Rayleigh was not all
| that certain about the results: The
| comparison of the present with former results throws
| an interesting light upon molecular magnitudes. It has been
| shown (Proc. Roy. Soc. March 1890) that the thickness of
| the film of olive-oil calculated as if continuous, which
| corresponds to the camphor-point, is about 2.0 mm while
| from the present curves it follows that the point at which
| the tension begins to fall is about half as much, or 1.0 mm
|
| [...] If we accept this view as
| substantially true, we conclude that the first
| drop in tension corresponds to a com- plete layer
| one molecule thick, and that the diameter of a
| molecule of oil is about 1.0 mm
|
| _XXXVI. Investigations in Capillarity:--The size of drops.
| --The liberation of gas from supersaturated solutions.--
| Colliding jets.--The tension of contaminated water-
| surfaces_
|
| If we assume that the "about 2.0 mm" value is just the
| previously mentioned 1.63 nm value rounded up, then that
| throws a wrench into the story, in particular this bit from
| blog post
|
| > Rayleigh's final result was 1.63 nanometers. Olive oil is
| mainly composed of fat molecules called triacylglycerols,
| and we now know that they measure about 1.67 nanometers in
| length, implying that Rayleigh's "primitive" estimates were
| off by just 2 percent
|
| is more of a numerological coincidence, the actual estimate
| that Rayleigh gives is _half_ of that!
| tech_ken wrote:
| > is more of a numerological coincidence, the actual
| estimate that Rayleigh gives is half of that!
|
| I definitely thought so too, in the first paper the 1.67
| isn't even really his primary guess so definitely some
| presentist bias in the OP
| bialpio wrote:
| From the paper:
|
| "The thickness of oil required to take the life out of
| the camphor movements lies between one and two millionths
| of a millimetre, and may be estimated with some precision
| at 1'6 micromillimetre."
|
| Looks like a primary guess to me, even if the table lists
| more data points.
| tech_ken wrote:
| Oh nice my bad, I was just looking at the tables
| jjk166 wrote:
| If there were multiple layers of molecules then the film would
| spread out over a wider area. With repeated experiments it
| would be clear that films are always an integer multiple of
| this thickness and never thinner.
| MereInterest wrote:
| Except that you could have part of the surface covered in 1
| molecule, and another portion covered in 2 molecules. Since
| you never directly measure the thickness, this would produce
| the same apparent thickness as a uniform 1.5 molecule thick
| layer.
| jjk166 wrote:
| That's not how fluids work. The molecules spread out to
| form an even surface everywhere, so you can't have local
| high spots. You'd have to put in enough oil to cover the
| entire surface, and then put in more.
| kccqzy wrote:
| Yeah and the point is that there is more embedded
| knowledge about surface tension here. For example if I
| put a small drop of water onto my desk, it does not
| spread out into a thin film of one water molecule thick.
| It remains a droplet due to surface tension.
| tantalor wrote:
| Scientists frequently have to make assumptions in order to make
| progress.
|
| Famous example is Darwin figured out that traits are
| inheritable by natural selection, and this is the driving force
| of evolution, without having any concept of the physical nature
| of DNA, or how genes could change (eg. by DNA mutation) to
| develop adaptations and thus make an organism more fit.
| kccqzy wrote:
| This is why I guess I was never really interested in
| scientific experiments personally and decided to study
| mathematics. These assumptions don't seem justified to me. At
| least in mathematics you always state these assumptions or
| hypotheses very clearly, or make them into axioms.
| tantalor wrote:
| I don't know if anybody challenged Darwin on that point.
| It's an interesting question.
|
| The simplest explanation is that he deduced such a physical
| mechanism _must exist_ but the science and technology
| available at the time could not locate it.
| taberiand wrote:
| Perhaps at the time it was sufficient to define "molecule of
| oil" as "the height of the amount when spread maximally across
| the surface of water", and it just so happens that height is
| only 1 actual molecule
| mda wrote:
| I have also immediately thought the same question. This is
| probably the most crucial part of the whole estimation and
| indeed left out in the article.
| bloak wrote:
| If you try the experiment lots of times with drops of different
| sizes you find the oil layer always has roughly the same
| thickness. That's an interesting observation that calls for
| some kind of explanation, and the hypothesisis that the
| thickness of the oil layer is the length of one molecule is
| perhaps the most obvious and plausible explanation. Then one
| would look for confirmation, of course. (What was the next
| thing to confirm this, historically?)
| shultays wrote:
| An idea: if oil forms a two dimensional shape, ie a single
| layer of molecules, then adding 2x amount of oil would give you
| twice the area. If it is three dimensional, say oil makes a
| bubble, then it would look smaller.
|
| Of course this also fails if the oil formed a disc of X layers
| of molecules
| Jeff_Brown wrote:
| And even assuming it's one molecule thick, how did he know how
| tightly the oil molecules in that layer pack together?
| cb321 wrote:
| The molecular scale was well estimated (at least for the
| gaseous phase of matter) by 1865 (25 years earlier not 5 as the
| incorrect HN title would suggest)
| https://physics.stackexchange.com/questions/13757/how-was-av...
| (and guesstimated by just "following your nose" in Gandalf-of-
| Lord-Of-The-Rings-ese in 1646!)
|
| Rayleigh's experiment is just accessible requiring _very_
| little training / background to describe. To interpret as a
| monolayer is honestly probably not so accessible at all,
| though, and a weakness of the atomsonly.news piece and
| seemingly not even done by Rayleigh himself. Modern retconning
| as zokier says elsewhere.
| bangonkeyboard wrote:
| I would have loved to have had a course in school about "The
| Design of Scientific Experiments." One that described the
| processes of landmark historical experiments from antiquity
| onward, and challenged students throughout: "Given this set of
| constraints, how would you design and execute an experiment to
| estimate the size of the Earth? Disprove phlogiston and
| luminiferous aether? Measure the speed of light?"
| dekhn wrote:
| I don't think many people today would be able to propose the
| Michelson Morley experiment and then actually do it. It was
| truly heoric (and Michelson was a genius).
|
| We did this oil/water experiment in freshman physics or
| chemistry lab. It was rushed, everybody just did the minimum,
| the teachers barely explained any of it, and then we moved on.
| _dark_matter_ wrote:
| I agree. The Michelson Morley experiment reminds me of some
| difficult algorithms: simple only in hindsight, and
| implementation is _hard_ to do correctly.
| buescher wrote:
| People still win Nobel prizes (LIGO, for example) using
| interferometers. It's arguably the single greatest invention
| in experimental physics.
| bsder wrote:
| Experiments are _HARD_. There is a joke among physicists that
| theoreticians are washed up by 35 but experimentalists don 't
| even get started until 45.
|
| To make a physics experiment work you have to be ridiculous
| about recording details and have a _strong_ intuition. You have
| to design the experiment such that you can differentiate
| between "hypothesis wrong" and "equipment doesn't work"
| because _you don 't know the answer_.
|
| (For example: When they turned on LIGO for the first time, they
| almost immediately caught a great event. Huge victory party,
| right? Nope. They promptly ignored it assuming that something
| was wrong with the machine. And it was only after significant
| post analysis and correlation that they decided that it was a
| real event.)
| andreareina wrote:
| The lengths they're going to fix the "loopholes" in the Bell
| Inequality tests are amazing.
| raverbashing wrote:
| 100% true
|
| And this is my sticking point with a lot of "Science
| skeptics" around that have skepticism as their personality
|
| Make no mistake, I do take scientific discoveries and
| knowledge very serious, and knowing the stories make it
| appreciate more the efforts and the work it took to get there
|
| But a lot of times people think the experiments give a very
| clear-cut results, when it's more like "one line is squiggly
| down and the other is squiggly up" with data being barely
| over 5 sigma
| cchi_co wrote:
| That would have been an incredible course!
| CountHackulus wrote:
| We recreated this experiment in one of my university physics
| classes. It was a lot of work, and our results weren't nearly as
| good, but it was instructive and interesting. The equipment
| requirements were completely reasonable for an undergrad physics
| lab. I highly recommend giving it a try if you can.
| metadat wrote:
| How is the measurement for the area the oil has spread over
| performed? Visually or some other way?
| opencl wrote:
| The actual manuscript from Rayleigh [1] explains it better: the
| area is the entire area of the vessel the oil was placed in,
| and the thing actually being measured was how much oil was
| required for it cover the whole area.
|
| [1]
| https://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/old_lite...
| dekhn wrote:
| Some powder is added to the water, which covers the surface of
| the water but not the oil patch (which is circular). Then the
| oil patch diameter is measured.
| misnome wrote:
| This was how we did this when we replicated this experiment
| in high school. I guess from the other responses here that
| this wasn't common?
| dekhn wrote:
| The original way was to cover the surface of a round bowl
| with oil. It certainly makes a lot more sense to me than
| trying to measure a floating disk of oil.
| wa2flq wrote:
| When we did it in high school (70's) we just used compound
| that had a long chain (soap?) and only one end dissolved in
| the water. It was very easy to measure and calculate the
| size of the molecule . We had a series of these simple
| experiments. Another I recall was measure the speed at
| which certain volatile compounds moved through the air.
|
| I definitely learned that all science doesn't have to
| involve complex equipment.
| ummonk wrote:
| He used a fixed area (a 33 inch diameter bowl) and measured the
| weight of oil required to just about calm the entire water.
| That turned out to be 0.81 milligrams.
| alnwlsn wrote:
| These are the best kind of posts, where there's something I've
| never even heard of before. I never knew 'oiling the seas' was a
| thing, or that it (apparently?) works.
| dr_dshiv wrote:
| I won't trust this until I myself can calm an acre of water with
| a teaspoon of oil. (Or at least see a YouTube video of someone
| doing it)
| isp wrote:
| YouTube video:
| https://www.youtube.com/watch?v=RST_ylwVrUw&t=1m27s
| shortstuffsushi wrote:
| That's funny, thanks for sharing. I was watching his video
| where he's saying "you can see it right there, look how much
| calmer it is, it looks like ice" and was thinking "I don't
| know what he's talking about I don't see ... oh, that ice
| patch is water"
| eesmith wrote:
| Another version is in Phil Morrison's "The Ring of Truth"
| episode "Atoms" at https://youtu.be/WQ3mjb9BSaU?t=1765 or
| 29:26 at https://archive.org/details/TheRingofTruth/Ring.of.T
| ruth.S01... .
|
| (It would be nice if archive.org had a way to link to a
| specific timestamp.)
| Terr_ wrote:
| That reminds me of the Millikan & Fletcher oil-drop experiment
| [0], which measured the charge of the electron.
|
| In short, microscopic atomized oil droplets had their fall-time
| through air measured to figure out their volume, and then a known
| electric field was used to levitate them. The calculated charge-
| per-molecule clustered around multiples of a smaller value, which
| would be the charge of an individual electron.
|
| [0] https://en.wikipedia.org/wiki/Oil_drop_experiment
| n_plus_1_acc wrote:
| How can you make sure you don't end up with 2e as a result? (Or
| any other multiple)
| Terr_ wrote:
| In 1909 the results results were couched in some "elementary
| electric charge" quantity, since the now-familiar subatomic
| particle model (and the "electron") was still gaining
| acceptance.
|
| I expect that the greater the number of trials, it becomes
| easier it is to detect a distinction between closer-
| multiples, and if at some point more trials stops changing
| the answer then you've likely converged on e, unless there's
| some new principle like "X-ray exposure only affects charge
| in in multiples of e greater than one."
| adrian_b wrote:
| The approximate value of the elementary electric charge had
| been known since 1874, when it was first computed by George
| Johnstone Stoney. After Stoney, other experiments had
| reduced the uncertainty with which the value was known, but
| it remained relatively high.
|
| The importance of the experiments of Robert Andrews
| Millikan consists in the fact that the uncertainty of the
| value of the elementary electric charge obtained by this
| method was much smaller than by any previous method (he
| claimed that it was better than one half of one percent,
| but he used wrong values for the viscosity of air, so his
| actual result was off by more than that, but still by less
| than one percent from the correct result).
| dekhn wrote:
| He did- he selected the lowest value, ignoring all the
| multiples.
| ceejayoz wrote:
| Not ignoring the multiples; the multiples verify the
| result.
|
| If you calculate the charge of one at 1e and you measure
| 2.5e, something went wrong. All values must be a multiple
| of the lowest.
| nkmnz wrote:
| You do. Thae size of the steps between the results is the
| "quantum" of a single transferable charge.
| SyzygyRhythm wrote:
| For that to happen, you would have to be very unlucky: all of
| your measurements would have to be 2e, 4e, 6e, etc. If a 3e
| or 5e sneaked in there, you'd realize that the charge was e,
| not 2e. With enough measurements, you can be confident that
| you've hit all the expected multiples of the quantum.
| db48x wrote:
| Not quite so. They did end up measuring a multiple of the
| fundamental electric charge. The experiment really measured
| 3e, 6e, 9e, etc. It turns out that the electron and proton
| have an electric charge 3x bigger than that of a quark.
| Since the experiment didn't generate any free quarks,
| nobody noticed for years. Even today the mistake persists
| and school children are taught, unironically, that down
| quarks have +- 1/3 of the fundamental indivisible unit of
| electric charge and that up quarks have +- 2/3 e.
| wholinator2 wrote:
| No need to nitpick, the original comment states perfectly
| accurately that he was measuring the fundamental charge
| _of the electron_, from which the constant e is derived.
| We've been using e to mean _electron_ charge for a very
| long time. Where do you get the idea that constant has
| anything to do with quarks?
| db48x wrote:
| https://i.kym-
| cdn.com/photos/images/original/000/992/402/c35...
|
| But seriously, it really is time to fix all the chemistry
| textbooks so that the charge of the electron is +3
| instead of -1.
| empyrrhicist wrote:
| Why, to make all that quark chemistry a bit easier?
| db48x wrote:
| Because electric charge is quantized, so measuring it in
| thirds is just dumb.
| ForOldHack wrote:
| "I see a clock, but I cannot envision the clockmaker. The
| human mind is unable to conceive of the four dimensions,
| so how can it conceive of a God, before whom a thousand
| years and a thousand dimensions are as one?" -Albert
| Einstein
|
| It would have revealed a lower layer of higher
| understanding.
|
| No one has been able to calculate the mass of a quark:
|
| "Nobody has seriously calculated theoretically a quark
| mass from first principles. So there is no issue of
| agreement with experiment. They are parameters in
| experimental fits, but sometimes remarkably consistent
| across a broad range of experiments-- and the QCD/EW
| calculations using them as inputs. If someone pretends to
| know their origin, he/she is bluffing."
|
| But the exercise is extraordinary!
| pdm55 wrote:
| There is always more to the story:
|
| https://www.scribd.com/document/661270387/My-Work-with-Milli...
| Fletcher & Millikan
|
| https://www.youtube.com/watch?v=B-uWaEvXqbA
| kqr wrote:
| They tried a similar experiment first, called the water drop
| experiment. It was intended to work in the exact same way,
| except with the obvious parameter varied: they would use water
| instead of oil.
|
| The reason the water drop experiment failed was that the bright
| lamps they used to look at the drops evaporated the water too
| quickly.[1] Such a relatable experience!
|
| [1]: https://buttondown.com/entropicthoughts/archive/when-
| bubble-...
| xenocratus wrote:
| Luckily it wasn't my grade that got this experiment as the
| practical exam in one of the National Physics Olympiads I went
| to... :) poor souls, most got answers orders of magnitude away.
| IncreasePosts wrote:
| A few days ago, there was a HN post about surface acoustic wave
| filters, and a commenter mentions how inspired the inventor of it
| must have been(https://news.ycombinator.com/item?id=41604937).
|
| That was this same fella!
| arvindh-manian wrote:
| Related: Agnes Pockels' experiments [0]
|
| [0]: https://en.wikipedia.org/wiki/Agnes_Pockels
| carlob wrote:
| Ten years earlier and she didn't publish it right away. That
| really goes to show how much more difficult it was for a woman
| to become a scientist back then.
| RachelF wrote:
| Semi off topic:
|
| Interesting to look at picture of the text of the 1890 paper.
| That typesetting is almost the same as modern scientific papers.
|
| Maybe Rayleigh had an early copy of LaTeX? ;-)
| buescher wrote:
| Thank Knuth for TeX or good scientific typesetting would be a
| nice thing the Victorians had.
| wwarner wrote:
| In 1676 Roemer estimated the speed of light by timing the orbit
| of Jupiter's moon Io, noting that as the Earth approached
| Jupiter, Io emerged from behind Jupiter a little earlier every
| day, and as the Earth traveled away from Jupiter it appeared a
| little later every day, with the time of day varying by 22
| minutes over a year. Knowing the difference between the two
| distances, he reckoned that light travels that distance in 22
| minutes, or 227 thousand km/s. The actual speed is about 300
| thousand km/s. Not bad!
| DaoVeles wrote:
| I always appreciate these stories about how very specific
| observations that most people would miss can give away far
| deeper details of the universe that many wouldn't even
| consider. Eratosthenes using shadows and figuring out the size
| of the earth within a few percent is another well known one.
| cchi_co wrote:
| It's amazing to think that with nothing more than a telescope
| and careful timing, he managed to get so close to the actual
| speed of light.
| NeoTar wrote:
| Well, also knowledge of the distances between the objects
| involved (at least the Earth and Jupiter), which in turn
| depended on a series of further investigations.
|
| Which is not to denigrate the achievement, but if I were to
| drop you on an alien world with only a telescope and an
| accurate time keeper, you're not going to be able to recreate
| it.
| zokier wrote:
| > if I were to drop you on an alien world with only a
| telescope and an accurate time keeper, you're not going to
| be able to recreate it.
|
| But you can relatively easily derive the distances too with
| timekeeper and telescope, by applying Keplers laws?
| wizzwizz4 wrote:
| One can, in principle. Most people lack the talent. (It's
| a skill that almost anyone could learn, but that doesn't
| make it a skill everyone _has_.)
| foggyjvdfghhv wrote:
| That's not the definition of talent
| wizzwizz4 wrote:
| From what I've seen, talent is the tendency for a person
| to naturally develop a skill, if left alone to do so. It
| isn't some kind of intrinsic capability.
| shthed wrote:
| https://en.wikipedia.org/wiki/R%C3%B8mer%27s_determination_o...
|
| https://en.wikipedia.org/wiki/Speed_of_light#First_measureme...
|
| Another interesting thing about using the timing of moon
| eclipses:
|
| > Galileo proposed a method of establishing the time of day,
| and thus longitude, based on the times of the eclipses of the
| moons of Jupiter, in essence using the Jovian system as a
| cosmic clock. The times of the eclipses of the moons could be
| precisely calculated in advance and compared with local
| observations on land or on ship to determine the local time and
| hence longitude.
|
| https://en.wikipedia.org/wiki/Galilean_moons#Determination_o...
| ForOldHack wrote:
| The speed of light, because it is so fast, is the most precise
| physical constant known : 299 792 458 m / s. Less than
| 7/1000ths away from 300,000,000 m / s. I am not going to sweat
| this in the least.
|
| So light travels only 0.3 m / nano second, or 11.802 inches.
|
| https://www.youtube.com/watch?v=9eyFDBPk4Yw
| Neikius wrote:
| Armed with this fact thinking about electronic devices. How
| the front of the signal travels and how suddenly the distance
| matters. Was blown away when I first thought about this.
| glial wrote:
| Therefore in one cycle of a 3GHz processor, light travels
| about 4 inches. Wild.
| xhrpost wrote:
| Which is maybe part of the reason RAM needs to be so close
| to the CPU? Granted though most RAM access takes several
| CPU cycles.
| Brusco_RF wrote:
| My favorite riff on this: at a previous job we worked on a
| 12GHz SERDES, which meant each inch of the cable had a
| different data bit on it
| qsdf38100 wrote:
| Speed of light has recently been redefined, and is now
| _exactly_ 299792458 m/s. It's no longer a measurement, it's a
| definition.
| hollerith wrote:
| That's a little misleading: either the meter or the second
| has been redefined to make c = 299792458 m/s.
| ghkbrew wrote:
| The second is (and has been) defined independent of
| length for a while. It's the time it takes for a certain
| number oscillations of a caesium atom.
|
| The meter was redefined as the distance light travels in
| a specific time. So you could say that either the meter
| or the speed of light was redefined to make the speed of
| light a round constant, but not the second.
| thimkerbell wrote:
| "Rayleigh divided the volume of the oil by the area it covered,
| thus estimating the thickness of the oil film. Assuming that the
| oil formed a single layer of molecules -- a monolayer -- then the
| thickness of the oil film is the same thing as the length of one
| oil molecule.
|
| This is how Lord Rayleigh became the first person to figure out a
| single molecule's dimensions, many years before anyone could see
| such molecules."
| pechay wrote:
| We did this same experiment in school, with a tiny pinprick of
| oil, estimating the volume of the drop as a sphere, and a small
| water tank, and then estimated the area of oil slick as a circle.
| nmstoker wrote:
| Yes, we did it in physics at school too, when we were 13 or 14
| I think.
| FredPret wrote:
| Very cool.
|
| For more like this, check out this lecture series:
| https://www.thegreatcoursesplus.com/the-evidence-for-modern-...
|
| It's by a guy called Don Lincoln and it's about how we
| established things like the existence of atoms, the speed of
| light, and many other fundamental things that are good to know.
|
| It's also an audiobook, though the lectures are easier to follow.
| dilawar wrote:
| I went to a talk by a very old physicist. At the end of his talk,
| he said, recalling from memory, all of the great experiments of
| the past were done by nothing. If an experiment costs more than
| $100, I am out.
|
| His setup has mud in a jar and bacteria in it which you can see
| with a simple microscope or handheld lens.
| AlotOfReading wrote:
| That's a bit harsh. To give one counterexample, the Michelson-
| morley experiment put the figurative nail in the coffin of
| centuries of speculation about the "luminiferous aether". The
| experimental apparatus was a table-sized precision carved slab
| of sandstone floating in a huge vat of mercury, holding the
| highest precision optical equipment of the day. I suspect it
| cost rather more than $100 even in the 1880s.
| veltas wrote:
| Although it was a refinement of the Fizeau experiment which
| conceivably could have cost $100 in living memory.
| ziofill wrote:
| >"not more than a Tea Spoonful," according to his diary --
| Franklin poured it onto the agitated water. The oil spread
| rapidly across the surface, covering "perhaps half an Acre" of
| the pond and rendering its waters "as smooth as a Looking Glass."
|
| What??
| imp0cat wrote:
| Here's a video from another post:
| https://news.ycombinator.com/item?id=41630637
| Summerbud wrote:
| > I love this story because it shows, at least anecdotally, how
| deep scientific insights can emerge from the simplest of
| experiments. It's a testament to the idea that you don't always
| need sophisticated equipment to unlock the secrets of nature --
| sometimes, all it takes is a drop of oil and a bit of ingenuity.
|
| This can apply to many other fields too!
| quantadev wrote:
| The credit for proving the existence of atoms is more often
| associated with Einstein's explanation of Brownian motion and
| Jean Perrin's experimental confirmation, even though earlier work
| by Lord Rayleigh, Benjamin Franklin, and others hinted at the
| molecular structure of matter.
| cwillu wrote:
| Site has gone down with a dns error of some kind; anyone have a
| snapshot?
| nes350 wrote:
| https://archive.is/oMgPW (The domain of the original article
| seems to be dead)
| rkagerer wrote:
| This is fascinating, but wasn't it still a bit of a conjecture to
| assume the oil would spread to a minimum thickness of one
| molecule? Did he have any doubts, like that surface tension might
| keep it thicker? Or other clues hinting it was indeed a
| monolayer?
| nielsbot wrote:
| My question exactly.. I hope someone can chime in :)
|
| EDIT: Thinking a bit more... I suppose it's a reasonable
| assumption that the molecules (mostly) wouldn't stack on top of
| each other. They all want to get lower and perhaps the
| resistance to the oil spreading out is much lower
| proportionately that the gravitational force encouraging the
| oil to flatten
| lIl-IIIl wrote:
| But if I spill some oil on my plate it doesn't look a
| molecule thin to me. Why is it different with water?
| OvbiousError wrote:
| I guess oil is repelled by water, so when it's poured on
| top of water it's more like floating on top. So the water
| pushes up, gravity pulls down and the oil molecules pull on
| each-other, there is no horizontal friction, allowing the
| oil to spread out this way. Whereas the oil does slightly
| stick to your plate, as can be observed when moving the
| plate around, so it won't spread as thinly?
| MereInterest wrote:
| There's a couple of possible reasons. First, you probably
| spilled more oil onto the plate. In the experiment, 0.81
| milliliters of oil spread out until it covered a circle
| with diameter 84 cm. Most spills would be more than a mL of
| oil, and most plates are much smaller.
|
| Second, most plates aren't flat. If you have an area of the
| plate that is at a lower elevation than the rest, the oil
| would pool up in that area.
|
| Third, even if you fill the plate with water, you could
| have elevation changes due to surface tension of the water.
| If the water is concave up, the oil would float upward and
| form a ring around the edge. If the water is above the
| surface of the plate, held in just by surface tension, the
| oil would float upwards and form a bubble at the center of
| the plate.
|
| Fourth, you could have something else on the plate that
| acts as an emulsifier. Whether a bit of egg, some pasta
| water, leftover detergent, these would break up the oil and
| prevent a film from forming.
|
| The easiest way to have a flat surface is to do the
| experiment in the center of a much larger body of water,
| since any effects from the surface tension would be at the
| edge.
| zokier wrote:
| I believe this is at least part of the explanation.
| Although there might have been some further developments in
| the 100 years since this was published
| Oleic acid on water forms a film one molecule deep,
| in which the hydrocarbon chains stand vertically on the
| water surface with the COOH groups in contact with
| the water. Acetic acid is readily soluble in
| water because the COOH group has a strong secondary
| valence by which it combines with water. Oleic acid is not
| soluble because the affinity of the hydrocarbon
| chains for water is less than their affinity for each
| other. When oleic acid is placed on water the acid
| spreads upon the water because by so doing the COOH
| can dissolve in the water without separating the
| hydrocarbon chains from each other.
| When the surface on which the acid spreads is sufficiently
| large the double bond in the hydrocarbon chain is
| also drawn down on to the water surface, so that the area
| occupied is much greater than in the case of the saturated
| fatty acids. Oils which do not contain active
| groups, as for example pure paraffin oil, do not
| spread upon the surface of water
|
| https://zenodo.org/records/1429064
| akarve wrote:
| there has to be some missing information on how he found the
| area of water that fully consumed exactly that amount of oil as
| it simply doesn't make sense without that. for instance one can
| spread a teaspoon of oil over 1, 2, n square meters and at some
| point the oil goes from m later thick to one to less than one.
| superjan wrote:
| Such an experiment was described in a science book I read as
| a kid. They dissolved oil in alcohol so as to measure a very
| small quantity of oil, and then a a knitting needle was used
| to stretch the oil film across a plastic container filled to
| the edge with water (until the film breaks).
| gnramires wrote:
| Perhaps he was observing the layer making sure it had
| integrity? Oil layers famously have an optical effect
| (iridescence from interference of reflections). This effect
| would transition as the layer goes from >= 1 molecule thick to
| <= 1 molecule thick (on average). It's likely possible to
| pinpoint this transition experimentally and then using the oil
| volume obtain the molecular layer thickness.
| tony-allan wrote:
| https://www.atomsonly.news/p/franklin-oil
|
| Why this domain has been suspended
|
| Since January 2014, all ICANN accredited registrars (like
| Namecheap) have been required to verify the contact information
| (Registrant Whois) of customers registering domain names. This
| includes modifications to the contact details.
| tony-allan wrote:
| Fixed!
| rkagerer wrote:
| Fun fact: Every 4 days humanity produces enough oil to cover the
| entirety of the world's oceans.
|
| _Source: Public statistics and my back-of-napkin math, not
| accounting for waves._
| cchi_co wrote:
| Even back in the day, without all our modern technology, great
| minds like Franklin and Rayleigh could uncover truths that still
| resonate today.
| donkeybeer wrote:
| Its not ancient times, some of the most accurate measuring
| instruments of that time are of a precision that you'd still
| need a few hundred or thousand dollars to buy today. The
| tooling wasn't primitive by any means.
| adrian_b wrote:
| The title of this thread appears to be wrong, because the parent
| article says
|
| "But a little experiment that Rayleigh performed in 1890,
| inspired directly by Franklin's observations, is not nearly as
| well-known."
|
| Therefore Rayleigh computed the size of molecules in 1890, not in
| 1870 (in 1870 Rayleigh was young and not known yet for any
| original research).
|
| While Rayleigh has devised a novel method for determining the
| size of molecules, it should be noted that the first who has
| succeeded to determine the size and weight of molecules was
| Johann Josef Loschmidt, in 1865.
|
| https://en.wikipedia.org/wiki/Johann_Josef_Loschmidt
|
| The publication of the weight and size of air molecules by
| Loschmidt is one of the most important milestones in the history
| of physics.
|
| Until that moment in 1865, the theory of atoms revived by Dalton
| could still be considered as some kind of fictitious model that
| explained some features of the chemical reactions and of
| thermodynamics, but which might have been wrong and which would
| probably be replaced by some better model.
|
| Starting from that moment, the atoms and molecules could be
| weighed and counted, so their reality was no longer questioned.
|
| The determination by Loschmidt of the size and weight of air
| molecules was enough to determine the sizes and weights of any
| other known atoms and molecules, making use of the relative
| atomic weights that could be determined from chemical reactions
| and which were already known.
|
| Moreover, a few years later, in 1874, George Johnstone Stoney has
| used the results of Loschmidt together with the theory of the
| existence of an elementary electric charge published by Maxwell
| one year before, in 1873, to compute the value of the elementary
| electric charge. Some years later, Stoney has given the name
| "electron" to the elementary electric charge, which has been the
| source of a very large number of words in modern science and
| technology, from electronics to hadrons.
| OvbiousError wrote:
| Cool article. They somehow got the formula wrong though, the
| formula on the screenshot has an additional factor of 0.9 that
| accounts for the fact that 1l of oil is not 1 kg. Perhaps it's
| intentional, but for something so simple I don't think it needs
| to be dumbed down even further.
| jll29 wrote:
| Thanks for covering that story - I lived at Clapham Common for
| seven happy years.
|
| So much history: there is also a little church on the Common,
| whose past members played a role in the abolishion of slavery:
| https://en.wikipedia.org/wiki/Clapham_Sect
| kitd wrote:
| > and he charted the Gulf Stream's course across the Atlantic
| ocean, noting that ships traveling from America to England took
| longer than those going the opposite direction
|
| ?? Has the Gulfstream changed direction in the intervening years?
| kopirgan wrote:
| Very interesting indeed!
|
| Was he just lucky that the spread was 1 molecule thick or that's
| the way oil spreads on water? Why?
| yapyap wrote:
| wow, he really had some knowledge for a lord
| ForOldHack wrote:
| He had time to think. Something so rare these days.
|
| 30 years later, Henry Cavendish measured G and estimated the
| density of the earth. Using candles, mirrors and telescopes.
|
| https://en.wikipedia.org/wiki/Cavendish_experiment
| rendall wrote:
| We performed this experiment in high school chemistry and it has
| remained with me as one of my deepest aha moments.
|
| It has become fashionable in foodie circles to mock the idea of
| adding oil to boiling pasta so as to prevent stickiness. The
| argument against seems to be that oil floats and cannot possibly
| affect the pasta, unless you add so much that the pasta becomes
| slimy. But I maintain that a drop of two in boiling water is
| enough to coat all the pasta in a single layer of molecules. The
| agitation of the water spreads the oil evenly as a kind of
| colloidal suspension.
|
| All these fancy restaurants with elaborate methods to avoid
| sticky pasta.
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