Radiator Leak: Newsletter Challenge (02/20/07)

I'm guessing, but if the sunglasses are of the polarizing type, would a mirage not largely disappear, but water won't?

Another way could be to observe how the direction of the 'water' shifts if one moves some distance perpendicular to the direction of the 'water'. If the direction (compass bearing) shifts, it's water; if not, it's a refraction image of the blue sky, essentially at infinity.

I think that because it is early afternoon the sun would be directly above them.

This would mean that if it was real water there would be no reflection as the sun wouldnt reflect from the water into their eyes. The sun glasses take the brightness out of the equation thus confirming the mirage as they would see nothing but some sand. The sand is at an angle reflecting light from sun directly towards them where as water can not do this.

Any remarks

This would mean that if it was real water there would be no reflection as the sun wouldnt reflect from the water into their eyes.

The sun mightn't reflect directly off the surface but then it wouldn't reflect of the temperature shift either. It's the incoming radiation from the Sun that is heating the ground that causes the mirage.

The mirage like the water is a reflection of the sky from behind through a shallow angle and it is this reflection that makes it look like water.

Are you led? Or lead? If you are lead, don't try swimming in the water, mirage or not!

Wilfy

Hi Wiffy

"Are you led? Or lead? If you are lead, don't try swimming in the water, mirage or not!"

I am assuming that you are referring to my quote

We the unwilling, lead by the unqualified, have been doing the unbelievable for so long with so little that we now feel confident attempting the impossible with nothing.

You are absolutely correct and lead is a metal and it should be led.

Congratulations and go to the head of the class you have spotted the deliberate mistake. I have been putting a deliberate mistake in my quotation since I joined CR4 and to date this has been the longest running unspotted deliberate error. It has taken about 5 months to spot so you have done well.

Of course you realize that I now need to think up an even more subtle mistake for the next quote!

By the way why don't you join CR4, you are obviously astute, observant and witty and you would probably enjoy the discussions.

Talk about ego. Were you lead'n enough to let this gurue thing to to yer head?

It's got nothing to do with ego it's just a bit of fun I have and an observation of human nature. By the way how many times did you read the quote before noticing the mistake and if you did notice it why did you not comment.

How inhumane! Because, let us say, I'm just slow on the uptake?

Hi there,

I also noticed your "lead" spelling. I didn't point it out because I feel rude pointing out every mistake people make, especially when said mistake is not germane to the issue being discussed. Maybe I'm just too much of a weenie, but if you spend your time pointing out little errors people make, you'd have no time to do anything else.

Anyway, that's my too cents ;)

Wade

At any rate guest, whoever you are, it was actually a complement that you noticed the mistake and had enough confidence to actually say something about it. The others that have noticed and commented on previous deliberate mistakes have taken it in the spirit with which it was intended.

Gee,

Do all your queries get such a plethora of replies? apart from the supplementary challenge of finding Masu's deliberate mistake, although I am afraid that I can't compliment him on this one as it was fairly easy to spot.

Let me say deliberately, compliment.

Now that is funny... Nice job Guest.

Masu,

The reason why nobody says anything about minor mistakes is mostly not to offend anybody. This site is worldwide and not everybody has a perfect grasp of the written english (I, for one, don't - being a "frenchman" from Quebec, Canada). Basically, just a matter of respecting the differences....

just my 2 cents...:)

Rick.

And, farthermore, now that you have announced yourself as a post-er of deliberate mistakes (!?) and observer of human natures, let us also hope - henceforth - you are a glutton for punishment.

"Sometimes, human nature exposed is human nature in one's face."

--Anon.

In your quote, the second "to" should be "too".

Hank

the others WHO have noticed, not THAT have noticed

Musu,

That's Wilfy, if you please,

your quote could also say:

"We the unwilling, leading the unqualified, have been doing the unbelievable for so long with so little, that, we now feel confident attempting the impossible with nothing."

Me thinketh yr quote needeth another 'o' - to simple!

"If the human mind were simple enough to understand, the human mind would be to simple to understand itself."

You have made a more fundamental error than the obvious "to/too".

You have already identified the subject in the second section of the quote, making the subsequent "itself" redundant. Unless you were referring to the initial "human mind" in which case the second stating is redundant.

ie. should read, either

"If the human mind were simple enough to understand, it would be too simple to understand itself."

or

"If the human mind were simple enough to understand, the human mind would be too simple to understand it."

Your quote establishes ownership twice, making for a very scrappy and linguistically incorrect sentence.

That is all.

Pete.

Musu,

That's Wilfy, if you please.

My sincere apologies Wify, have you ever thought of registering?

Mash-U

How about calling Wilfy WiFi?

My hat's off, you caught one out of three--answers to your own question, that is. And, yes, I'm thinking about it; but, still trying to get this mirage thing figured out...

I'm wondering, FYI, whether the fact that hot mirages are always inverted has anything to do with it the answer. I'm also wondering it the (yes, polarized) shades would be turned ninety degrees...since a sky reflection (perhaps?) ought to be polarized vertically...due to unidirectional heat escape from the burning sands. If the image appeared to appear and disappear as the shades were rotated, they might then know that the water was not real?

Another thing: if it's a true mirage in a hot desert then the intrepid travellers would really only be faced with how far away the objective really is, not whether it exists. Of course, a water pool (as in, oasis) in the (hot) desert ought to have greenery (and mirage reflection of same) associated with it (unless it's poisonous or salty). So, without a tree or two, the adventurers could conclude, with or without glasses, that they would not want salt water for their radiator--or toxic water to drink once they walked (after the radiator ran dry) to the water image.

Pay no attention to that interloper behind the curtain.

Masu? Are you still here?

MASU is still here, I have just been off on other threads. I have just come back to this thread and found some 40 new posts, all I which I have not hat time to read yet. The upshot is that since I live in Australia I plan to carry out some experiments with a couple of polarizing filters that I just happen to have lying around. I planned to carry out the experiments today but unfortunately the wind was to strong and would not let mirages form.

So hang in there folks I havn't forgotten about everybody and with a little luck and the right weather I hope to test out all the theories within the next day or two.

Jorrie?

Well, interloper, guess Masu and Jorrie hurried off in a rush to the bottom.

"I'm wondering, FYI, whether the fact that hot mirages are always inverted has anything to do with it the answer."
I think not - other than being the reason that they look the same as reflections. This is a case for some simple drawings (not my forte)

"I'm also wondering it the (yes, polarized) shades would be turned ninety degrees...since a sky reflection (perhaps?) ought to be polarized vertically...due to unidirectional heat escape from the burning sands."
Images from real water are partially polarised horizontally. For some directions of view, so is skylight from near the horizon. (Polarising sunglasses are polarised vertically so that they attenuate both of these)

"If the image appeared to appear and disappear as the shades were rotated, they might then know that the water was not real? "
I think, in non-tropical regions of the northern hemisphere that:
no_change = mirage
change = water.
(See post #53 - if you have reason to differ, I'd be happy to learn - thanks)

"Another thing: if it's a true mirage in a hot desert then the intrepid travellers would really only be faced with how far away the objective really is, not whether it exists. Of course, a water pool (as in, oasis) in the (hot) desert ought to have greenery (and mirage reflection of same) associated with it"
Unfortunately, that could be a bit of a myth. You can get patches of greenery without accessible water in many deserts, and temporary patches of water without additional greenery as well.

Fyz

Thanks Fyz. Some of what you say are distinctions without differences. The sojourners only want to know real (close up) or mirage (far away); so it's of no concern which, normal or ninety degrees, removes or breaks up the vision.

True, plants can store and survive between waterings, or live on subterranean water; in which case, seeing vegetation, they might want to go to the plants, if not virtiual, to dig for water...but that's not the proposition is it?

It would be reasonable, to conclude that water alone would be water that does not support life, as in brackish, and possibly unfit for their purpose. Understand, though that this "myth" aspect was only introduced in a somewhat facetious spirit. Now, while I go off to examine #53, what about this? Suppose that the shades are yellow - i.e., blue blockers!. What do you suppose then? Would a mirage reflection appear differently than an actual image? Be back in a bit.

Ross

The colours are shifted relative to each other, so you would in theory get a different location for different colours. In much the same vane, I think a mirage will give an image that is somewhat stretched vertically. But I doubt that the shimmer that you get in the desert in the daytime would allow you to detect the difference without a heap of other equipment.

Fyz

I was wondering and wandering more in the following vein: If I view sky filtered through blueblockers (which typically are also polarize-coated but, no matter), the sky takes on a more grayish cast. One might suppose, moreover, that the reflected (mirage) light from the sky will also change hue when filtered the same way. Perhaps, however, viewing water through the filter would not be so affected as to change its apparent color. Therefore, if the apparent pool and the sky above it showed the same, grayish hue, then our friends might conclude they were seeing a mirage. If, on the other hand, the objects appeared with different hues--the sky gray and the water image not gray--then they might conclude that the supposed water is actual water in their line of sight. What do you think?

If I understand the question correctly: for low-angle reflection, both types of reflector will pretty-much reflect all colours to the same extent, and this applies to each polarisation separately. This is somewhat different to reflections at steeper angles to the surface, where dispersion of refractive index can have more effect, but even there I wouldn't expect large differences for water. So I would expect the changes in the sky colour and in the reflected colour to be very similar whatever we do here.

Fyz

P.S - Re Masu: I see the spell-checker got me - but you corrected it.

Regarding spell checkers, I sure wish someone would come along with a typo checker. I find that I typically make the same mispellings...which are actually habitual typo's or when my ticker and fingers are running at different speeds. So I tend to make the same typing errors. Now, if a spell checker could train and recognize such patterns, or be taught to check certain words or word grouping...that would be great for this touch typist. Will think over your technical content and get back if....

The presence of a tree is only a partial indicator.

Trees grow and as the water table drops their roots grow down to follow the water. The water may be many metres below the surface - maybe 30m. Now if it's a young tree that's different. Scrub would indicate water near the surface.

On the other hand the lack of trees is also no indicator. Water in the desert tends to be high in alkali so water rising to the surface near a lake evaporates increasing the concentration of alkali, eventually poisoning the ground. The Leila Lakes South of Riyadh have no trees near them. The trees are about 3-4km away with water being conveyed to them from the lakes. The ground between the lakes and the present trees glistens with salt.

Archie

Wilfy here,

I have thought of registering, but business overtakes me.

By the way, fix your "to to" in your quote. You're not being very difficult.

It is always difficult to know whether to correct all the errors one sees, but led/lead always bothers me too, too much.

Wilfy

Methinks you may have missed an 'o' on one of the 'to's........

Keep having fun! Life is too harsh if you don't.

Best regards,

Don M.

Ok, that deliberate mistake was obviously no where near clever enough, I can see finding a suitably subtle deliberate mistake is going to require considerably more thought.

So where are the word police when people insist on using the possessive apostrophe to pluralize, use pseudo English like "yr" instead of "your" and completely skip capitalization. They should have just about everybody under the age of twenty in gaol serving life sentences by now.

NOWHERE, not NO WHERE

and you missed the question mark at the end of the second sentence; is it not a question????????????????????????????????????????????????????????????????????????????????????????????????????????????/

To all the anonymous cowards that like to criticize without showing their names.

If you posted any where near the 60,000 plus words I do each month I expect one could find numerous typographical, grammatical and spelling errors in your posts. As for my English sucking just have a look some of the other posts and you will see there are many considerably worse than mine. At least I make an effort to be reasonably succinct and put my mane to my work, which is something that you havn't.

If you wish to be the CR4 word policeman then that's fine, just meter out your criticism consistently and equally too all offenders.

I always thought that a person had to be looking in the general direction of the sun in order for the sun's rays to allow a mirage to "appear". Looking in a southeasterly direction in the early afternoon would be looking about 50 to 60-some degrees AWAY from the sun's direction, in the northern hemisphere, and roughly parallel to it, in the southern hemisphere. Since the question, as stated, provided no clarification as to which one hemishere the particular two (observers) were in, does that imply that those of us who assumed a particular one can be described as "hemi-centric"?

The question did say south westerly

Yes, but, if your ask an Australian, who has never left Australia, to draw a map of it, likely as not, they would draw it up-side-down to the north pole, because to them, the South pole is "up", and "south westerly" to them would be northwesterly to us (north-hemispherians ?) Thus, I think an actual Australian should represent their perspective on this issue before counting up any (votes) on it...

Never seen a map like that cobber.

Some years back there was a map circulating around that had the South Pole at the top and the International Date line at the center. I havn't seen one for a while but it certainly looked strange.

I always thought that a person had to be looking in the general direction of the sun in order for the sun's rays to allow a mirage to "appear".

The direction of the sun is fairly irrelevant to the formation of mirage. The important factor is that there is sufficient heating of the layer of air directly above the ground so that the density of the air reduces enough to bend the light and make it appear as if the sky is being reflected. What you are seeing is the sky directly above and behind the mirage and your brain is interpreting this as a reflection off the surface of water.

Provided the ground is hot enough a mirage will form and the position of the sun is only relevant in that it is normally the source of the heat that is forming the mirage.

IT ALL DEPENDS ON THE TIME OF DAY LOOKING SOUTH WEST AND IF YOU ARE ON THE SOUTHERN HEMISFER IT NOT A MIRAGE IN THE NORTHEN IN THE MORNIG IT IS NOT MIRAGE IN THE AFTERNOON THERE IS A POSIBILITY

pEDRO

I think your comment about lateral movement is ingenious, but it only applies if the extent of the temperature inversion is sufficient that the mirage is extensive, and you are only aware of it because it is reflecting a discontinuity in the sky. In any case, this type of extended mirage is not that likely to be mistaken for water. I suspect that John and Tom are looking at a localised variation in the reflection, due to the ground not being completely uniform.

BTW, I think you have the polarisation effects precisely reversed - see my post #38

Fyz

Hi Fyz, when you wrote: "BTW, I think you have the polarisation effects precisely reversed - see my post #38" you were perfectly right! I guess I had my sunglasses on upside down, or something!

Regards, Jorrie

Assuming that we are both correct now, what is more remarkable (concerning?) is that nearly everyone has agreed with your initial miscommunication.

Fyz

Hi, i think that sunglasses will reduce the brightness and the density of the mirage waves , therefore if this observed surely it is a mirage , but if not it will be surely a water.

I agree with Jorrie's post above.

Unless, maybe a mirage to the southwest of an observer in the early afternoon isn't even possible? I don't think it is likely, but I'm not sure.

The only other answer that comes to mind is that while Tom is rummaging through his pack, John pulls a gun and orders him to get out and walk to where they "see" the water to find out if its real or not.

Greg

In response to my post above:

WRONG:

"Unless, maybe a mirage to the southwest of an observer in the early afternoon isn't even possible? I don't think it is likely, but I'm not sure."

I goofed in my sense of direction and had it completely opposite. I was picturing the mirage being northeast of me in my mind, but thinking it was southwest of me instead. (Ouch!)

I live in the northeast US and felt that a "water" mirage is most likely when it is "between" the sun and the observer, and least likely when the sun would be to the back of the observer, (only I got my directions backwards). But since these types of mirages are generally a reflection of the sky, I don't know if that's true or not.

However, since the Challenge doesn't mention the location of Tom and John, maybe the direction of the mirage does have something to do with the correct answer?

Perhaps a member with more knowledge of mirages can shed some insight in that area.

Greg

Hi Greg,

As far as I know, one can see 'water-like' mirages from any direction where there is a blueish sky background and the right sort of temperature gradient above the surface (hot surfaces, like a tarred roads or desert surfaces).

Regards, Jorrie

Hi Jorrie,

Thanks!

Where I live, about the only mirages I ever see are on the roads, and I'm usually driving. I couldn't remember seeing them when the sun was to my back, but then I wasn't really paying any attention to that at the times I did see them.

I tried to research the direction issue but couldn't find any definitive information, and my feelings about directionality were only reinforced by the fact that I do know that the horizontal viewing angles of "water" mirages are relatively small.

Regards,

Greg

"the horizontal viewing angles of "water" mirages are relatively small."

So the answer may be to stand on the other person's shoulders, as high on the car as possible, thus changing the angle of vision enough to make a mirage disappear.

Hi Greg G,

Where I live, about the only mirages I ever see are on the roads, and I'm usually driving. I couldn't remember seeing them when the sun was to my back, but then I wasn't really paying any attention to that at the times I did see them.

I have seen mirages with the sun in just about any direction including set. I fly gliders and if you behind is a low to the ground as it is in a glider it's not uncommon to see a mirage on the runways. Actually with sealed runways it's pretty rare not to see one and the end of the runway is normally obscured by a mirage. As soon as you get airborne and a few feet off the ground the entire runway suddenly comes into view. This is usually a great relief because the mirages give you the impression that you are running out of runway far faster than you actually are.

Hi Masu,

Thanks for adding your comments about mirages in relation to their relative positions to an observer and the sun.

Between you and Jorrie, it has to be a fact!

Regards,

Greg

Masu -

In response to your quote below, your "to" is incorrect and should read "too" as in:

"If the human mind were simple enough to understand, the human mind would be too simple to understand itself

Since you said you would add delibrate mistakes to be caught I thought I better correct you.

Except it doesn't really matter...bluish or not, provided the context is suggestive of water; as in, say, an appearance of reflective or shimmering quality...as in the way roadway mirages usually appear...as you alluded to elsewhere. So, in essense, the perception of water is not a colorbound issue. Like the uninformed think of mirages, it's all in the head.

First of all it depends on where you are. If you are in Australia then all bets are off and the possibility of finding water in the desert is slim unless what you are seeing is a flash flood headed your way. In either case you are screwed so lets hope that the question is posed to people living in the northern hemisphere and you are looking towards the afternoon Sun.

As Jorrie has pointed out the use of a polarizing filter might be a considerable help. The reason being that a mirage, due to the nature of the mirage will be polarized in a horizontal plane so it will mostly disappear when a vertical polarizing filter is used.

However the surface of water is also horizontal and therefore the light reflected from it when viewed at a shallow angle will also be horizontally polarized. This means that there will be a considerable change in the appearance of the water as well when viewed through a polarizing filter.

The end result is that there will be a difference between true water and a mirage when viewed through a polarizing filter but it is not a simple as the mirage disappearing and the water remaining. Unless you have see it before you probably would not be able to tell the difference.

AS usual the challenge question has left out some important details like where you are and what type of sunglasses are being used, both of which could have a dramatic effect on what you see and how you interpret it.

Having said that the answer the challenge is looking for is most likely that the sunglasses are polarizing and that if it is a mirage then it will disappear then reappear when viewed through a rotating polarizing filter.

All you have to do (based on the assumption that we have polarized sunglasses) is turn your head sideways (looking vertically, so to speak) when looking at the 'horizontally polarized' mirage, and it should virtually disappear. (Just like when you go to a gas station and look at the digital display through your polarized sunglasses. It seems like there is no image, unless you take off your glasses or turn your head sideways while looking at the digital display. This is due to the polarization of the screen and your glasses.)

-A

Please do not continue to insult either mice, or elephants, because they are entities that actually work.. . . .

The mirages is at the worst when the sun is directly above.

An altenative use of sunglasses is to be able to read the map.

...except when the sun is beyond zenith--post meridian locally--during which the surface reaches its hottest--its worstest--temperature.

Presumably they are polaroid sunglasses. If Tom looks through these at the water and gradually rotates the glasses, then if it is a real pool of water, he should see a lessening of the glare off the water. Reflected light is partially polarised, so at some point in rotating the glasses the reflection will be minimised. This would not apply to a mirage.

I don't really know, never dealt with mirages. Does the answer have anything to do with looking at the 'mirage' mirrored in the glasses? Do mirages disappear in mirrors?

No that only works for vampires.

The effect is caused by the changing of the refraction index of air at different temperatures. On hot days the bottom layers of air actually reflects the light like a mirror.

The blue or grey sky is then seen on the ground with often a piece of brown above it.

Regulars in an area can see the difference very easily without resorting to Polaroid's etc.

The light should be polarised because the refraction is in one direction only.

The opposite effect also happens. Objects beyond the horizon can be seen on certain days.

The other posts seem to have the mirage versus real water covered, but that still leaves the leak. Ground black pepper is the best way to stop the leak until it can be properly repaired. I have seen it work in a fire truck where the fan went thru the radiator. I wouldnt have believed it if I wasn't there to see it with my own eyes. Pinch shut the radiator tubes at the hole, then throw in about a half pound of pepper, then fill with water. It held for about 2 hours at speeds approaching 70 miles an hour on the interstate while we drove it to the shop, where we had the radiator replaced among other things it needed. So if those 4-wheeling dudes had some black pepper with them, for their lunch, perhaps, that would do it, other wise they have to hold on until reaching a store or other place where they can get the pepper.

Also work too is raw egg, if the hole is small. (As seen by MacGeyer, the TV Show, and comfirmed by Rob and Ray auto talk show. )

MidniteFighter

Always carry a number of RAW Eggs when driving through the dessert. A raw egg dumprd into the radiator filler will seal a small leak in no time while the coolant is still hot. Then you can drive on toward the mirage and see if it is real. Of course, both the Pepper trick and the Egg trick require that water is at hand to make up for the coolant loss before the leak was detected by the driver and the motor shut off.

I would just ride John's 4 wheeler to find the water.

That's what I would do.

they have two 4-wheelers...what about a tow??

Tom will throw a rock at the mirage....if it makes a splash then there's water. If it makes a "THUD" then it's a mirage....

How about just taking the second 4-wheeler for a spin to determine if the water is "real" or not?

Oh wait...guess #14 already said that.....never mind...:)

R.

Found this link on mirages:

http://science.howstuffworks.com/mirage.htm

A couple of things. First, who in their right mind goes four wheeling in the desert in the middle of the afternoon without any sort of backup plan in case of emergencies like this. Second, how does Tom notice the radiator leak? If John were following, wouldn't he be the one to discover the leak first? Or could it be that they were stopped and there was a giant puddle of mud below his four wheeler. In that case, there is only one good four wheeler to go to the possible water supply. But if this is the case then they need to patch the hole with something. Third and finally, if Tom were smarter, he would have already been wearing some sort of eye protection from dust getting into his eyes. Most likely, John knows it is water or not because he was the smart one in deciding to wear his sunglasses while riding. Tom doesn't know, could either get his glasses and see for himself, or just ask John if he is wearing his, which he should, because it is bright out in the desert, wouldn't you wear your sunglasses all the time if you had them?

Clever would have an air-cooled engine

The glasses are polarized.

Kelly

Tom has a pair of polarized sunglasses that will screen out the light from a mirage

as they are rotated from the horizontal through the vertical.

Steve

I recall seeing mirages in all directions the last time I stood in the desert.

Therefore, If Tom can definitely say there is one specifically to the southwest, then he should use the polarized glasses to look for variations in intensity (as stated before) when rotated 90° and if the visual indications remained then both he and John should Sally Forth towards the water with full knowledge that John could give Tom a ride home if I am wrong.

If I was John, I'd send Tom off - assuring him it wasn't a mirage - and fool around with Sally. She sounds like a fun girl.

Or, if both John and Tom are misogynists, they could send Sally - sounds more boring though.

Whether it is a mirage or not does not have much consquence. A lake will not fix the leak. I would use whatever means available to stop or slow down the leak and then use whatever drinking water we could spare to refill the rad. Then head directly to the nearest repair facility.

Don

If the sunglasses are polarized then laying one lens over the other and rotating them (like a quarter wave polarized plate) the mirage will disappear but real water wouldn't.

Just a guess but what the heck.........

Bill Mace

Polarized sunglasses, once very common in the 50's and 60's expecially with aviators, fishermen and boaters, block polarized light rays such as those given off by light reflected off of surfaces at certain angles, especially low angles of reflection. By using the polarized sunglasses you block the reflected rays that are parrallel to the orientation of the "polar-ized" lenses. Mirages are polarized light reflected off of surfaces such as sand, a road surface, water, etc. and the polarized sunglasses will block this reflected light. So if you look at the "possible water hole" and rotate the polarized sunglasses 180 degrees- If it disappears completely at some point it is a mirage, if it doesn't disappear it and only the reflection off it disappears it is then water.

This is often used by sailers to cut down on the amount of light reflected off of the water surface into their eyes, vehicle drivers to cut down on the glare off of road surfaces and by fishermen to greatly reduce the glare off of water so that they can see the fish under the water surface!

If you stack two polarized lenses so that you are looking through both of them, rotating one of them will eventually completely darken your field of view. The direction of polarization of each lense is at right angles to each other at this point. This was used at one time to make adjustable shade protective goggles, such as those used in steel mills.

They could melt the plastic sunglasses to fix the leak.

SFIK, depending on how you look at it, mirages are caused by refraction or by total internal reflection. In neither case would there be a significant polarising effect on the light. By contrast, shallow-angle reflection from the surface of water causes significant polarisation. I'll assume that, although he may have lacked common sense, Tom was not deluded, and that the sunglasses are of the polarising type.

If John and Tom are well outside the tropics and also in the northern hemisphere, the mirage will be in the general direction of the sun, but slightly to the west of it, and the incoming sky-light will be largely unpolarised; therefore, the reflection in the water will change significantly as they rotate the sunglasses, and the reflection in the mirage will be roughly constant.

If they are in the tropics or the southern hemisphere, things won't be quite as simple - as the incoming light source is already partially polarised. Nevertheless, if the reflector is water, the proportion of reflected light will be smaller for horizontal orientation of the sunglasses than for vertical orientation; if it is a mirage the proportions will be roughly the same. Note that, for this case, using the sunglasses at angles in between horizontal and vertical can cause confusion.

I think that this means that I agree with Tesser, but disagree with the rest of you.

Unfortunately, it's far too cold here to test my theory. Perhaps someone from the Southern hemisphere would like to check using a local road - and possibly substituting NW for SW to take account of the US-centric orientation of the GlobalSpec team?

Perhaps I should have stated the conclusion more explicitly:

Assuming that Tom knows what he is doing, they will compare the 'reflection' with the background with the (polarising) sunglasses in the standard orientation. If the level of the reflection reduces relative to the level just above the reflection, it is water, otherwise it is a mirage.

They might be advised to check with the glasses in the perpendicular orientation, when the 'reflection' from water will reduce by somewhat less* than the background, whereas the reflection from a mirage will change similarly to the background.

*Depending on the international location of the desert, this may not be very visible, as the residual vertical polarisation could be so small that is masked by the imperfect polarisation of the sunglasses. However, either method should be fine throughout the northern hemisphere.

BTW, in the absence of additional information, and given that it is mid afternoon: our intrepid explorers should ignore the water, as it is unlikely to be sufficiently deep to be useful, and telephone the AAA using their mobiles. If they can't get a signal, they should try a temporary repair on the leaky vehicle, and then head off with both vehicles in the direction of the nearest service station, checking for signal and watching the temperature gauge of the leaky vehicle as they go. If/when the temperature starts to move, they should abandon the leaking vehicle and continue together in the sound vehicle. They could be well advised to leave a note on the leaky vehicle saying where they are headed)

If the sunglasses are polarized, a mirage will disappear, but water will still give a bright reflection.

As this postdates #38, please can you explain where that went wrong?

If the sunglasses are polarized and the water is a mirage, then the mirage will disappear and reappear by reorienting the sunglasses.

A plea to subsequent contributors - there seem to be two contradictory views on this. One forwarded by Jorrie (but without much conviction on his part), but much supported; the other initially proposed by Tesser, and supported (so far) only by myself. The plea is this - if you wish to support the majority view, please help us ignorant folk by explaining why we are wrong.

Fyz

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One well-reasoned argument is worth an infinite number of assertions. Anon

Tesser and Jorrie (and guest #54) are onto something...the same thing actually...but Tesser errs in distinguishing a mirage from a reflection. A hot mirage is a reflection, an inverted reflection. The rotation idea seems plausible since polarization of the image could be imparted by the direction of heat rising.

Are you saying that the rate of movement of the refracting air (<m/sec) has an effect on the polarisation of light (velocity 3E8m/sec)?

If you actually follow the path of the light in a mirage, you will follow a curving path. There is no point at which you can say it is reflected. That is to say that the light is not reflected in quite the same sense as it would be by water. The other point is that the distributed reflection from the mirage has to be of the nature of "total internal reflection", because there is no sudden discontinuity to cause any other type of ordered reflection. Total reflection is just that - no polarisation.

Tesser's post may not have been carefully enough worded for you - but that doesn't make him wrong.

Nor, if read carefully, did my post say that he is--wrong that is; only that, by inference, some might interpret...that he was drawing a conclusion in direct opposition to his...initial conclusion. Now let us mince words about the reflection thing about which you have taken me to task. To say that an object is continuously, internally reflected from a refractive boundary that follows the earth's curvature is not--I offer--to also say that somehow it is not reflected; or that I am incorrect--if such is what was intended. Please understand, it is of scant concern to me who proves right--and, if all are right that's just fine, too--nor does joining in a mutual admiration society admit as proof of a thing in my mind; ...guess you could say I am beyond disconcerting myself about such things. If we (or anyone) can reach a conclusion that more or less matches the secret solution to the challenge...that is just fine with me. If anyone, including this writer, proves in for a surprise, that's okay, too. I'd just as soon be newly enlightened as correct, or first, don't you see. ³

^{So I'll just keep plugging and endeavoring to comprehend, and hope for leniency & understanding in return.}

Maybe I'm too literal in my interpretation of English. To err is to move into error, which is to become wrong. And, so far as I can see, he gave his conclusion (correct), but then abbreviated his description of the alternative answer.
While on the topic, my attempted route to understanding has been to propose or espouse a theory and then test it. If I don't submit to this, I'm in danger of accepting the theories of whoever shout loudest. For me, the wait-and-see route at best ends up with isolated bits of knowledge, which I can't extend into other areas. In one way, it's a risky business, because it exposes me to being found incorrect...