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  #51  
Old 09-09-2019, 01:42 PM
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A diagram that isn't to scale is not a "misrepresentation."
Imagine my shock to discover that Alaska isn't an island off the coast of Baja California.
  #52  
Old 09-09-2019, 01:50 PM
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The very first result shows white, as do a lot of the other photos. I've been in plenty of white-lined pools and the water is still blue, or more of a light turquoise. Steps help to show the true color of the lining. https://www.tinostone.com/projects/casino-ibiza/
  #53  
Old 09-09-2019, 02:41 PM
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Moderator Note

Let's dial it back.

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Sorry
  #54  
Old 09-09-2019, 02:46 PM
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From angles and in weather conditions that allowed you to see blueness, which, I repeat, might often otherwise be completely ...absent.
OK, but (to continue with suitably dialled-back demeanour) the angle of view is not dependent upon the colour of the sky. I can look down on the water from a harbour wall, or Brighton pier on a sunny or cloudy day; I can look through the crests of breaking waves in summer or winter; I can (as we saw in the second linked video) go snorkelling on an overcast day, or under a clear sky - and in all of those situations, the sea is blue.

The reflection of the sky, on the surface of water, is different when the sky is different - but that is not what was falsely asserted to me at school - the assertion was: water is colourless; the sky makes the sea blue. This is demonstrably false.
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Old 09-09-2019, 03:42 PM
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Things "are" colors because they emit light, they reflect light, or they transmit light. I think we can agree that water does not emit light so it has color for one of the other two reasons. Usually, but not always, we thing of the color of something as the color it reflects.

Water transmits the portion of the electromagnetic spectrum that we call visible light. As this site points out, that is not a coincidence. Eyes evolved in organisms in the water. They were only useful if they were sensitive to the wavelengths of light available.

https://www.quora.com/Can-water-droplets-absorb-light

Actually you can see that water transmits blue light better than red. That is one reason why those nice natural light underwater photographs have a nice bluish tone to them.

But the more important reason is impurities. Tiny particles in the water (or air) preferentially scatter shorter wavelengths. Although all the colors pass through water, the blues are preferentially scattered and some of that scatter returns back through the surface to our eyes. If some impurities are somewhat larger, the green light is also scattered.
  #56  
Old 09-09-2019, 04:03 PM
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Originally Posted by Mangetout View Post
The reflection of the sky, on the surface of water, is different when the sky is different - but that is not what was falsely asserted to me at school - the assertion was: water is colourless; the sky makes the sea blue. This is demonstrably false.
It's still not a case of a scientific theory being wrong. Just one science teacher (or one book) being wrong.
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Old 09-09-2019, 04:08 PM
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(This may not quite meet OP's criterion.) Archimedes did find a way to determine whether a gold crown was counterfeit by immersing it in water, and the obvious displacement test deduced from scanty record and written up by the great Marcus Vitruvius Pollio was sound in theory.

But Archimedes did not test the gold crown with the simplistic 'Vitruvius' method described in story after story.
Quote:
... The difference in the level of water displaced by the wreath and the gold is thus ... 0.41 millimeters. This is much too small a difference to accurately observe directly or measure the overflow from considering the possible sources of error due to surface tension, water clinging to the gold upon removal, air bubbles being trapped in the lacy wreath, and so forth. Additionally, the change in water level would be even less than 0.41 millimeters if the wreath had a mass of less than 1000 grams, or if the diameter of the container opening were larger than 20 centimeters, or if less than 30% of the gold were replaced with silver.
It seems that it was Galileo Galilei who first deduced that Archimedes took full advantage of his Principle of Hydrostatics by weighing the crown with a balance scale while it was immersed.
  #58  
Old 09-09-2019, 05:39 PM
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[snip]
Actually you can see that water transmits blue light better than red. That is one reason why those nice natural light underwater photographs have a nice bluish tone to them.

But the more important reason is impurities. Tiny particles in the water (or air) preferentially scatter shorter wavelengths. Although all the colors pass through water, the blues are preferentially scattered and some of that scatter returns back through the surface to our eyes. If some impurities are somewhat larger, the green light is also scattered.
[Emphasis mine]


Hmm...if you look at the absorption spectrum for water at a slightly more useful scale:

https://en.m.wikipedia.org/wiki/File...ient_large.gif

Youíll notice that blue is transmitted a whole lot more than any other color; based on that alone, light transmitted through any substantial depth of water is going to be largely blue anyway.

Obviously, light scattering due to nanoscale particulates is a thing. Rayleigh scattering plays a large role in the atmosphere, but atmospheric Rayleigh scattering primarily scatters blue light, making it a low-pass filter that transmits yellow and red light better than blue light.

Thatís a big reason why sunlight looks yellow, especially during the aptly-named golden hours at sunrise and sunset. But under water, blue light dominates.

Itís possible, of course, that ocean water looks blue from below because water transmits it preferentially while looking blue from above due to Rayliegh (or Mie or whatever) scattering.

Since water transmits blue light while mostly absorbing other colors even without scattering, Iíd love to see confirmation of your claim that the sea is blue mostly because of blue-light scattering.

In short: got a cite? I mean specifically for the claim that scattering plays a bigger role in making the ocean look blue than does the blue-transmitting absorption spectrum of water.
  #59  
Old 09-09-2019, 07:41 PM
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[
In short: got a cite? I mean specifically for the claim that scattering plays a bigger role in making the ocean look blue than does the blue-transmitting absorption spectrum of water.
Do I have a cite, no sorry. But when you're looking at a lake or ocean from above, you aren't seeing the transmitted light. The light source is from above the water surface so the transmitted light stays below the surface. I don't see how the transmitted light could have anything to do with the blue color we see except under water as I noted.
  #60  
Old 09-09-2019, 09:15 PM
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Do I have a cite, no sorry. But when you're looking at a lake or ocean from above, you aren't seeing the transmitted light. The light source is from above the water surface so the transmitted light stays below the surface. I don't see how the transmitted light could have anything to do with the blue color we see except under water as I noted.
If you are thinking of Rayleigh scattering which preferentially scatters blue light -- that is why the sky is blue, but my understanding is that it only happens with free (gas) molecules, not molecules bound up in liquid or solid.

When you look into the ocean, what you see is light scattered by particles (dust, plankton, etc) floating in the water. These particles are generally much larger than the wavelength of light, so scattering is not preferentially blue. It's mostly "white", i.e. the same color as the light shining on the particle. And because water preferentially absorbs red & green light, that light shining on the particle is blue.

Wikipedia has a whole page on color of water, with a section specifically on color of lakes and oceans, which backs me up on this. It also discusses the reflection of the sky as being one component of it.

Last edited by scr4; 09-09-2019 at 09:15 PM.
  #61  
Old 09-09-2019, 10:51 PM
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Wikipedia has a whole page on color of water, with a section specifically on color of lakes and oceans, which backs me up on this. It also discusses the reflection of the sky as being one component of it.
If you look at the surface of water at greater than the critical angle (I forget the exact number but around 48 degrees for water), most of the light you see will be a direct reflection of the sky. The greater the angle, the more the light will be reflected. That Wiki section shows this in both pictures, even the first one which ostensibly "manifest[s] water's inherent blue color." Almost all the light in that first picture is reflected. You can tell this because the color of the sky changes from being light near the horizon to darker blue higher up. The water color is lighter near the horizon to darker lower down. Furthermore, the sky has some higher clouds on the left making that part lighter and this is reflected in the water color, being lighter on the lower left.

So if you're on a body of water and you look out over the water, the color is going to be mainly a reflection of the sky. If you look down, the color will be that of the water or impurities within it. If there's significant waves, you'll get a mix of the two depending on the exact angle, which of course will be constantly changing. (In fact that second picture has more waves, so the water doesn't reflect the sky as well as the first one.)

Last edited by dtilque; 09-09-2019 at 10:52 PM.
  #62  
Old 09-09-2019, 11:05 PM
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If you look at the surface of water at greater than the critical angle (I forget the exact number but around 48 degrees for water), most of the light you see will be a direct reflection of the sky.
Critical angle is where total internal reflection happens. But that only happens when you are inside a denser (larger index of refraction) medium looking at a boundary with a less dense medium - e.g. you are underwater, looking up at the surface. It doesn't happen when you are above the air, looking into water.

Reflectivity of water surface (i.e. looking at the water from air) does depend on incident angle, but it's less than 50% until you are ~85 degrees from normal (i.e. your line of sight is at ~5 degree angle relative to the water surface).

Last edited by scr4; 09-09-2019 at 11:07 PM.
  #63  
Old 09-10-2019, 01:18 AM
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The still pervasive belief that being out in the cold causes 'a cold'.

(and ninja'd by Nemo on ulcers)
A cold is caused by contracting a respiratory virus.

But cold weather can lower your immune systemís ability to fight infection, and make you more susceptible to contracting a virus. Therefore the advice to stay warm in order to protect yourself from catching a cold is still valid, even if the reasoning behind it is not.
https://journals.plos.org/plospathog...l.ppat.0030151
  #64  
Old 09-10-2019, 01:35 AM
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Do I have a cite, no sorry.
I see.

Quote:
Originally Posted by OldGuy View Post
I don't see how the transmitted light could have anything to do with the blue color we see except under water as I noted.
I gather youíve never been to the Caribbean.
  #65  
Old 09-10-2019, 11:10 AM
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It's still not a case of a scientific theory being wrong. Just one science teacher (or one book) being wrong.
Agreed (and acknowledged when I first raised it in this thread). I think it was a fairly common falsehood in the 60s and 70s, though)
  #66  
Old 09-10-2019, 11:12 AM
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Do I have a cite, no sorry. But when you're looking at a lake or ocean from above, you aren't seeing the transmitted light. The light source is from above the water surface so the transmitted light stays below the surface. I don't see how the transmitted light could have anything to do with the blue color we see except under water as I noted.
If the transmitted light stayed below the surface, the ocean would appear black. If you can see anything at all when it's underwater, it's because some of that transmitted light is being reflected back up (and is undergoing transmission again on the way back up)
  #67  
Old 09-10-2019, 11:22 AM
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. . .But cold weather can lower your immune systemís ability to fight infection, and make you more susceptible to contracting a virus. . . . .[/url]
I don't think this has ever been proven. If it were the case, we should see an uptick in all kinds of illnesses during colder months--and we just don't.
  #68  
Old 09-10-2019, 12:44 PM
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Dinosaurs became extinct (probably a direct result of that meteor that slammed down in the Yucatan) clearing the way for mammals to evolve. Mammals did not cause the extinction.
  #69  
Old 09-10-2019, 12:51 PM
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Also, water is blue in indoor swimming pools with no natural light.
It might be worth pointing out that copper sulphate (which is very blue) is added to swimming pools to control algae.

A bit of googlage gives a dose of 2 ounces for a 10,000 gallon pool.
How much that would affect the colour of the water?
  #70  
Old 09-10-2019, 01:20 PM
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I don't think this has ever been proven. If it were the case, we should see an uptick in all kinds of illnesses during colder months--and we just don't.
Cold season.

Flu season.

And thanks to anti-vaxxers, measles season, etc. is back.

This should not be new information to people.

The issues are the factors involved: weather, school in session, people around people more, etc. The belief that cold weather and such doesn't encourage colds has been challenged quite a bit in recent years.

Last edited by ftg; 09-10-2019 at 01:22 PM.
  #71  
Old 09-10-2019, 01:33 PM
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Dinosaurs became extinct (probably a direct result of that meteor that slammed down in the Yucatan) clearing the way for mammals to evolve. Mammals did not cause the extinction.
I've never heard anyone claim that mammals caused the extinction of the dinosaurs, and in any case, mammals had already evolved by the event; the removal of dinosaurs allowed mammals to spread, diversify, and dominate.
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  #72  
Old 09-10-2019, 01:50 PM
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Cold season.

Flu season.

And thanks to anti-vaxxers, measles season, etc. is back.

This should not be new information to people.

The issues are the factors involved: weather, school in session, people around people more, etc. The belief that cold weather and such doesn't encourage colds has been challenged quite a bit in recent years.
Thanks for the response. . . Now where in that does it support the point that cold weather depresses the immune system, and where does it show the spike in all other the diseases that you would expect with a depressed immune system ?
  #73  
Old 09-10-2019, 02:06 PM
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A cold is caused by contracting a respiratory virus.

But cold weather can lower your immune systemís ability to fight infection, and make you more susceptible to contracting a virus. Therefore the advice to stay warm in order to protect yourself from catching a cold is still valid, even if the reasoning behind it is not.
https://journals.plos.org/plospathog...l.ppat.0030151
It (the cold) also causes more people to congregate indoors, making spreading said virus much easier.

So - being cold does not cause you to catch a cold - but it does make you more susceptible to doing so.

and no amount of "dressing warm" will change that.
  #74  
Old 09-10-2019, 02:47 PM
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Isn't it also the case that the cold and dry air in winter dries out the mucous membranes which reduces their effectiveness in filtering out airborne diseases? It's not exactly reducing the immune system's ability to fight infection, but reducing the pre-screening effectiveness of the upper respiratory system.
  #75  
Old 09-10-2019, 05:06 PM
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I've never heard anyone claim that mammals caused the extinction of the dinosaurs, and in any case, mammals had already evolved by the event; the removal of dinosaurs allowed mammals to spread, diversify, and dominate.
In the past it was sometimes suggested that mammals could have contributed to the extinction of the dinosaurs by eating their eggs, or even by competition. (In fact, my first dinosaur book, Roy Chapman Andrews' All About Dinosaurs (1953), makes these suggestions as a couple among several causes, and the chapter on the extinction is headed by an illustration of couple of ratlike mammals eating a clutch of dinosaur eggs.) And the idea was common in popular culture:

Quote:
You know Tyrannosaurus Rex was destroyed before
By a furry little ball that crawled along
The primeval jungle floor
He stole the eggs of the dinosaur
...
We are egg snatchers -
Flashin' sunshine children
Diamond thieves
Mau Mau (Amerikon), Jefferson Starship (1970)

Last edited by Colibri; 09-10-2019 at 05:08 PM.
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