In 1870, Lord Rayleigh used oil and water to calculate the size of molecules
atomsonly.news
atomsonly.news
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.
But you can relatively easily derive the distances too with timekeeper and telescope, by applying Keplers laws?
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...
So light travels only 0.3 m / nano second, or 11.802 inches.
Does make me realise I don't know so much about the super low level parts of it beyond electrons and holes. One end of the wire needs to be at a lower potential to encourage electrons to flow from that side to the other. Hmmm.
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.
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.
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."
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).
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.
But seriously, it really is time to fix all the chemistry textbooks so that the charge of the electron is +3 instead of −1.
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!
https://www.scribd.com/document/661270387/My-Work-with-Milli... Fletcher & Millikan
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-...
Thanks for submitting! Would welcome suggestions for any other publications on how scientific theories were first discovered.
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
Can you elaborate on that? What experiments did the professor perform?
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.
Asimov was incredibly talented.
https://en.wikipedia.org/wiki/Asimov's_Guide_to_Shakespeare
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.
"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.
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...
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).
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.
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.
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.
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.
Hunt for Vulcan is a fun history lesson with some interesting insights about human nature. It's history of science, not science. It took about 3 hours to read and I had a lot of fun with it.
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.
You don't have to include the boring bits of who paid for the research or the day to day lives of the researchers. That isn't science, and it doesn't help the student understand science. A mere description of the fact that Tycho Brahe kept meticulous records of the positions of the planets in the sky and a walkthrough of the math that shows this data matches elliptical orbits and the math that shows that Newton's laws lead to those elliptical orbits is sufficient. The fact that there is a discrepancy for Mercury motivates further developments.
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...)
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.
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...
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.
Even our math teacher would tell us the stories of how mathematicians "came" to their solutions.
A good teacher makes such a huge difference
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."
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
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.
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
There's no reason why the volume you get when each oil molecule is surrounded on all sides by other oil molecules should be the same as when each oil molecule has air above and water below. Can anyone explain why this is so?
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.
If this seams impossible, remember that when water freeze into ice, it expands to a 3D "net" with empty holes.
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.
Or did he pour it into a huge lake or something?
He didn't. It was an assumption
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.
> 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
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 μμ 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 μμ
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 μμ
If we assume that the "about 2.0 μμ" 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!
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
"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.
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.
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.
Of course this also fails if the oil formed a disc of X layers of molecules
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.
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.
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.)
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
"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.
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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.
That was this same fella!
30 years later, Henry Cavendish measured G and estimated the density of the earth. Using candles, mirrors and telescopes.
His setup has mud in a jar and bacteria in it which you can see with a simple microscope or handheld lens.
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
Source: Public statistics and my back-of-napkin math, not accounting for waves.
This can apply to many other fields too!
?? Has the Gulfstream changed direction in the intervening years?
https://en.m.wikipedia.org/wiki/Chronology_of_computation_of...
(It would be nice if archive.org had a way to link to a specific timestamp.)
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? ;-)
Was he just lucky that the spread was 1 molecule thick or that's the way oil spreads on water? Why?
[1] https://www.damtp.cam.ac.uk/user/gold/pdfs/teaching/old_lite...
I definitely learned that all science doesn't have to involve complex equipment.
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.
What??