Wikipedia:Reference desk/Archives/Science/2006 July 26

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Talking starling video on YouTube

http://www.youtube.com/watch?v=VpYHYrMnffc&search=starling

What do you guys think of this? I'd heard that pet starlings were capable of learning a few words - but this one seems particularly talented. Just how intelligent are starlings in comparison to other talking birds? I guess we see so many of them that we don't really pay any attention to them. --Kurt Shaped Box 01:04, 26 July 2006 (UTC)

It's fake. Watch the bird when it whistles. It doesn't open it's mouth, just makes noise. Also watch the throat feathers when it whistles - they move quite a bit.

Now compare to talking - every single time it opens it's mouth you hear words - but if you notice, the feathers don't always move! And birds don't need to move their mouth to talk, yet here, ONLY when it opens it's mouth - and EVERY time, it opens it's mouth, you hear talking.

And finally listen carefully to the words it's saying - every single time, it sounds EXACTLY the same, as if a computer was playing a sound file. If it was real it would vary a little. 71.199.123.24 21:31, 27 July 2006 (UTC)

Our starling doesn't talk but does impressions of twenty birds, plus the  dog down the road and Curly of the three Stooges WOOB WOOB WOOB WOOB WOOOO. He performs every morning about 6:30 and has been doing this for 8 years.

Should I turn off my computer during a thunderstorm?

I get pretty annoyed when I have to unplug the computer during a thunderstorm, and I want to know if this is really necessary. Here this concept is talked about and most of the answers are yes. But I want to know what are the chances of this happening? Would this happen once in a hundred thunderstorms? Once in a thousand? Is it as important to do this as it is important to wear a bike helmet? Or as important as "do not lay, sit or sleep on this electric blanket" or "Do not exceed the weight limit of 215 lb on this trampoline"? --Jonathan ^talk 01:42, 26 July 2006 (UTC)

When you unplug your computer in a thunderstorm, it has nothing to do with your personal safety - it's for the safety of your computer. Wearing a bike helmet, or not breaking your neck on a trampoline are issues of personal safety, so it's hard to compare their relative importance; I assume your head is priceless to you compared to your computer... in terms of damage to your computer, if you use a good surge protector, your computer has a decent chance of surviving a lightning-related surge. In terms of the frequency of surges, I don't know, but they do occur. --Bmk 03:23, 26 July 2006 (UTC)

A friend of mine had their hard disk fried during a thunderstorm about six months back. it's a good move to unplug. Grutness...wha? 03:30, 26 July 2006 (UTC)

Unless you're the type that doesn't mind losing loads of important data, then yes you should turn it off. If you invest in a good UPS, you should be safe leaving it on if there are just a few small rumbles of thunder beacause the computer will remain on for a few minutes even if you lose power. I would still advise unplugging everything though if there are severe storms in the area. I once saw an episode of MythBusters that dealt with questions of this sort and if I recall correctly, they determined that you really don't want to be in contact with any electrical equipment if there are severe thunderstorms nearby. --Nebular110 04:24, 26 July 2006 (UTC)

If you don't like losing important data, you should have it backed up for precisely such an eventuality. - Mgm|^(talk) 13:24, 26 July 2006 (UTC)

Lightning can induce a sudden voltage on the phone wires that can blow out a chip in a modem. Not so much as to be dangerous to a human, but exceeding the voltages you can put on a chip. I've seen it happen. So, remove the phone wire from the modem, if you have a modem. Logically it would seem the same would apply to your DSL "modem", but I don't have direct experience of that. --GangofOne 04:55, 26 July 2006 (UTC)

It also depends on where you live. In the countryside you often have long overhead telephone and electrical distribution lines. Those are more susceptible to induction from lightning than shorter underground cables used in cities. Also trees that brush against overhead lines and fall down on them during storms cause grief, which doesn't happen with cables. But if you live out in the sticks you already knew this :-) Weregerbil 08:07, 26 July 2006 (UTC)

This may also depend on the country you're in. If electricity and telephone lines or cables are supplied by private companies (that actually compete) then if protection against this is so costly that it noticeably increases the price any company that does this will go out of business because people generally focus more on short term gain. I don't know if this is the case, but it sounds plausible.

Also, if there is such a risk, then that is a good argument to have backups on different media, such as on dvd's (in a different location if possible) or possibly on hard disks on a separate (old) computer that isn't normally connected. DirkvdM 09:31, 26 July 2006 (UTC)

AAAHHH! I just found out too late that those new LCD tv's are remarkably sensitive to a little speck of distant lightning. I had put surge protectors on all the computers, but not on the little tv in the exercise room. I then read that sometimes you can find the resistor that fried, but this one has all surface mount stuff, and the inside appears to be working perfectly, except it doesn't work! I'm now wondering about a happy way to ditch it.... --Zeizmic 12:05, 26 July 2006 (UTC)

Okay, thanks for all the answers. I was mostly trying to find an excuse to keep the computers running, but seeing as I do have backups for most of my important files, I might be okay. --Jonathan ^talk 12:18, 26 July 2006 (UTC)

Many people purchase a spike protector for the computer, including a port for the phone line. This protects against voltage spikes, but not against an actual lightning strike.

I had a modem get fried during a thunderstorm once, so I'd say it's not all that rare. StuRat 02:53, 27 July 2006 (UTC)

Mr Wheeler, of Wheeler's formula for inductance fame

What is his full name? What years was he born and died? What year did he come up with the Wheeler's formula for inductance. Any other information on his biography?

Gary Burger

I can't find much centralized data online, but after some intrepid searching, here's something to get you started - the citation for the paper in which he developed the Wheeler formula for inductance:

• Harold A. Wheeler, "Simple Inductance Formulas for Radio Coils," Proceedings of the I.R.E., vol. 16, no. 10, October 1928

Hope it helps --Bmk 06:32, 26 July 2006 (UTC)

Lizard

What type of lizard has a black body with yellow spots?

The kind at Camp Green Lake are Bearded Dragons. Hyenaste ^(tell) 05:19, 26 July 2006 (UTC)

Salamanders? But they are amphibians.....Paul venter 18:38, 26 July 2006 (UTC)

What's the Deal With Water Boiling at Altitude?

I was under the impression that it boils at a lower temp, but I've also heard from somebody about it taking longer to reach boiling point. The two seem incongruous to me. Any answers? And why?

The lower the air pressure, the lower the boiling point, therefore, the higher the altitude, the lower the boiling point (generally). I don't know about it actually taking longer to boil, maybe someone else knows about that. It might have to do with transfer rate of heat, I don't know.--Anchoress 05:21, 26 July 2006 (UTC)

It is illogical that it would take longer to reach the boiling point. However, food cooked at higher altitudes will take longer to cook since it is cooking at a lower temperature. Hyenaste ^(tell) 05:25, 26 July 2006 (UTC)

It makes sense that a substance would reach the STP boiling point after a longer time, though, as the extra heat would be "absorbed" by the enthalpy of vaporization, leading to cooling by evaporation. That said, the liquid wouldn't be at STP, so that doesn't really apply. Titoxd^(?!?) 05:34, 26 July 2006 (UTC)

That's what i thought. I remember that you can't fully cook some kinds of beans up at high altitude because the proteins don't break down until you reach a higher temperature than the water can go (unless in a pressure cooker.) Thanks

The deal is, once the water hits the boiling point, whatever that might be at a given pressure, all extra heat goes into energy of vaporization; you can't heat a liquid hotter than its boiling point! Therefore, if the boiling point is low somewhere (such as at a high altitude), the temperature at which you can cook food in the water is lower, so it takes longer to cook. --Bmk 06:36, 26 July 2006 (UTC)

Not always: you can superheat water in a microwave (of course, it more or less explodes when you then disturb it, so it's useless for cooking anyway). — Lomn | Talk 14:03, 26 July 2006 (UTC)

Or use a pressure cooker...

Silly question?... but

What stops something from going faster than light? I am reading a physics book so I wont fail while taking the ap class in my highschool along with 5 other killer courses, and i came upon the formula for the fairly obvious (to us now) fact that a falling object accelerates at a constant rate (in other words its velocity continues to grow with time.) What is to theoretically stop a highly compact mass dropped from the farthest edge of the gravitational pull of a very heavy, compact planet with little wind resistance (friction, etc) of any kind to overcome the speed of light? What is the theory behind this "cosmic speed limit" and why isnt the hypothetical situation a major physics theory clash?

A lot of things can move faster than light, provided they have no mass. A simple example would be the intersection of 2 lines forming an acute angle and moving apart at relativistic speeds or lower; with a very small angle of intersection even small speeds would be sufficient Paul venter 18:35, 26 July 2006 (UTC)

The hypothetical situation doesn't happen because of a few things. Firstly, the acceleration due to gravity isn't a constant, it's actually inversely proportional to the square of the distance from the centre of mass (according to Newtonian physics, at least - if you want to make things accurate you need to work in General Relativity, to which Newtonian physics is a reasonable approximation for many things but not perfect), so to even get the amount of acceleration you're thinking of, you'd need a very large mass, and a reasonable distance. Secondly, and more importantly, in relativity, the "effective" inertial mass of an object (ie. how hard it is to accelerate) increases with velocity, so that as an object's velocity approaches the speed of light, it becomes harder and harder to accelerate, and its mass approaches infinity. Much of the physics you would be learning at high school is based on approximations that only work in certain situations - low velocity, no particularly strong gravitational fields, and so forth. (Oh, and don't worry, as far as questions go, it's far from silly. If you're used to "traditional" physics, relativity and quantum mechanics are often quite counter-intuitive.) Confusing Manifestation 05:51, 26 July 2006 (UTC)

IANAAP (I am not an astrophysicist), but my understanding was that, since mass increases with speed, the speed of light is like the balancing point whereupon an object's increasing mass prevents it from going any faster. Or was it something more specific, as in anything going faster than the speed of light would be infinitely massive? I'm mixing up my Star Trek Physics with my real physics lol.--Anchoress 09:12, 26 July 2006 (UTC)

IAAAP (I am an Astrophysicist). I would recommend reading the general relativity article. You are pretty much along the correct lines (at least regarding changing mass). The relative mass of an object when travelling relatively to an observer is given by the rest mass multiplied by the Lorentz factor, gamma. which is equal to one divided by the square route of one minus the relative velocity squared over the speed of light on a vacuum squared (it's easier to see when written down properly). The upshot of this is that a body travelling at the speed of light in a vacuum (relative to an observer) would have an infinite mass (and therefore have required an infinite amount of energy to get there); if it were to travel faster than the speed of light it would have an imaginary mass - which is why it can't happen.

I read somewhere that light particles are really zero-time particles; that from their point of veiw, they don't exist at all. Don't ask me how that works, but that might be a clue as to why they always have to move so fast and why it's such a weird substance. --Jonathan ^talk 12:24, 26 July 2006 (UTC)

This is true Jonathan. There should be several good articles about explaining the exact mechanisms of this phenomenon so I wont go into a full explanation of them here. The upshot is that time flows at different rates for comoving observers. To calculate the time passed for an body relative to an observer, the observer must measure the time interval, and divide it by the Lorentz factor $1/sqrt(1-v^{2}/c^{2})$ where v is the speed of the moving body (relative to the observer). From this you can see that when v=c time will cease to pass for the moving body (relative to the observer). This effect is knows as time dilation.
Going hand in hand with time dilation is the phenomenon of length contraction. Distances (in the direction of movement) of a body will appear shorter for an observer. The method for calculating this is the same as with time dilation except that time is replaces with distance.
Taking both of these phenomena into account, if you were to ride on a photon you would observe everything to ever happen in the whole history of the Universe happen at exactly the same instant and at exactly the same (infinitely small) place!

weather - temperature change in same area

(moved from the Help Desk) I would like to know what causes a noticeable temperature change in 2 or 3 days in the same area. Other than temperature all other weather conitions appear the same - one period to the next.

Thank You - bl —The preceding unsigned comment was added by 4.158.195.191 (talk • contribs) 21:39, 19 July 2006 (UTC)

Weather at nearby locations, such as warm or cold fronts moving through an area, will affect local temperature (presumably you aren't taking that into account when you say "all other weather conditions appear the same," but I might be wrong). Another possible cause (not sure how strong it would be) is that a number of sunny days could warm up a large body of water, then over the course of a few cloudy days the water would slowly cool. Probably that effect would be rather small though. Digfarenough

Steak on a black eye

I have often seen on television (I know...never trust the damn thing, but I wanted to know) people holding streaks to a black eye for some kind of comfort or relief. Sometimes they are compltely frozen, and sometimes it is just a raw (although I assume chilled) steak. This perplexes me for a varitey of reasons.

1) While the steak might be cold, what about the meat juices and such that would come out from contact with your face if it was raw and the melting of the ice around the steak by your body heat? Isn't that dangerous and/or yucky and disgusting?

2) Is there anything actually IN the steak (chemicals or etc.) that help reduce the pain, swelling, or discomfort of a black eye? I figured maybe that's why they do it.

3) Why even use a steak in the first place? If you have a freezer with a steak in it, wouldn't you probably have ice or some other very cold foodstuff (a bag of frozen peas for example) that would work just as well as a frozen steak?

Thanks, --69.138.61.168 07:00, 26 July 2006 (UTC)

One advantage that comes to mind is the fact that cold steak (if it isn't frozen) is malleable; it can fit better on your eye better than peas can. --Kjoonlee 07:57, 26 July 2006 (UTC)

Not so, Kjoonlee. A bag of frozen peas will be quite malleable, as the peas only stick together (when they do) in small clumps. —Daniel (‽) 08:37, 26 July 2006 (UTC)

The steak thing comes from the 1930's madcap movies and 40's cartoons. At that time, it was probably the only cool thing from the icebox, and it was only 5 cents a pound! For any impact injury or strain (sprain), you can ice it with a gel pack. Always put a cloth inbetween, and only do it about 10 min at a time. --Zeizmic 12:26, 26 July 2006 (UTC)

E=MC²

Why is it that energy and mass are interchangeable? It does right? But why?

See E=mc² and General Relativity -Benbread 09:12, 26 July 2006 (UTC)

No need for general relativity. Special relativity will do nicely. --198.125.178.207 16:57, 26 July 2006 (UTC)

My college physics teacher explained it partially by dimensional analysis: Energy equals work equals force times distance equals mass times acceleration times distance, so the units of energy are (kilogram*meters^2)/(second^2). The units of mass are kilograms the units of velocity of light or anything else are (meters)/(second). So other than some proportionality constant due to the units used, it pretty much has to work out that way, and there was nothing surprising in the equation. It could not be, say E=MC, or E=MC cubed, or E=the square root of (MC) or the measurement dimensions would differ on each side of the equals sign.

When Uranium fuel is used in reactor, its mass decreases by about 1%, which multiplied by c squared gives the energy given off by the fission reaction. If an equivalent amount of energy were given off by burning coal, oil, or gas in a power plant, the mass of the fuel plus the combustion oxygen would decrease by the same number of kilograms. If a metal cube were simply heated up without any chemical or nuclear reaction, the weight of the metal would increase by an amount equivalent to the heat energy added divided by c squared. Both these weight changes would be too small to measure practically.Edison 20:49, 29 July 2006 (UTC)

About the main parts of an experiment.

what are the main parts of an experiment?

• Perhaps you want to see scientific method? —Mets501 (talk) 09:49, 26 July 2006 (UTC)

It also depends on what type of experiment you are trying to do. Iolakana|^T 12:37, 26 July 2006 (UTC)

I think you'll do better with the article experiment. --198.125.178.207 16:58, 26 July 2006 (UTC)

protists

the importance of protists to all other living things

This sounds a bit like a homework question, please do your own. You can start with protist and ecosystem. The protist kingdom is large and plays a variety of different roles in a variety of different ecosystems. Emmett5 15:04, 26 July 2006 (UTC)

The diference

I want to ask a simple question (maybe for you) but it still make me confuse What's the diference between Radio frequency and intermediate frequency?

Take a look at superheterodyne receiver. Basically, you tune a radio by mixing (multiplying) a local oscillator with the RF signal to bring it down to the IF (intermediate frequency). Then, the electronics that convert the signal from the IF to audio frequencies do not have to be tuned and are cheaper because they are not high frequency, high bandwidth components. —Bradley 16:01, 26 July 2006 (UTC)

Master/Slave for CD-ROM/CD-RW stuff

OK, so I've put all of my hardware into a new computer tower (with a new motherboard and CPU--yay!) but I forgot which settings on CD drives determine its master/slave position. One of the CD drives has its master/slave jumper look like this:

* I *
* I *

and the other looks like

* * I
* * I

(Where "*" means a pin and "I" means a plastic piece)

Which is which? The ikiroid (talk·desk·Advise me) 16:25, 26 July 2006 (UTC)

• Unfortunately, there's no real standard, and the jumper positions differ between different makes and models. Unless it's marked on the drive itself (it quite often is), look up the drive's model number on-line and find the instructions from the manufacturer's website. --Bob Mellish 16:36, 26 July 2006 (UTC)

And don't forget to check out our shiny new Computing Reference Desk. However, the reply above is exactly right. --LarryMac 16:45, 26 July 2006 (UTC)

Oh.....I didn't even see the new reference desk. Sorry about that. The ikiroid (talk·desk·Advise me) 17:30, 26 July 2006 (UTC)

Well, while there's no official standard, there's a de facto standard for CD drives (unlike HD drives, which tend to be all different). I just looked at an old CD drive I had, and the settings are: right jumper for master, middle jumper for slave, left jumper for cable select (so, your first one would be the slave and the second one the master). It's also always or almost always written on the drive itself (look carefully near the jumpers; you probably will find the text as a relief on the plastic there). --cesarb 17:41, 26 July 2006 (UTC)

OK, I checked the drives and you were right, Cesar. They're labeled (albeit barely). And I'm 86% sure that on the ribbon, the middle connector goes to the slave, right? And the end connector goes to the master? The ikiroid (talk·desk·Advise me) 17:56, 26 July 2006 (UTC)

The cable doesn't matter if you have the drives set to Master/Slave. The cable only matters if you set them to CableSelect. --Kainaw ^(talk) 18:00, 26 July 2006 (UTC)

In fact, it does matter; AFAIK, one of the things the master/slave setting selects is which drive has the termination. The termination should always be at both ends of the ribbon; so, you must put the master at the end of the ribbon, and the slave at the middle (if you have a single drive, it must always go at the end of the ribbon). --cesarb 22:18, 26 July 2006 (UTC)

A small note: after doing some searches to find out more about it, I have seen about the same number of people claiming IDE is terminated and claiming IDE is unterminated; if it's unterminated, the only requirement would be that both ends of the cable are used. I have even seen someone claiming it's terminated only on the faster UDMA modes (which would explain why some say it is and some say it isn't, and also makes sense). I have also seen people saying that it's important to plug the correct end of the cable to the motherboard (the blue one) on 80-wire cables (because the extra wires are grounded at only one of the plugs). So, to avoid any possible problems, it's better to be safe and plug the blue end to the motherboard, the black end to the master, and the middle gray connector to the slave. --cesarb 23:15, 26 July 2006 (UTC)

I have found on some cd drives that the master/slave/cable select lables are embossed into the casing on the top of the drive above the jumpers. These can be difficult to see if the drives are dusty. Hope this helps

Testosterone or DHT increases muscle size?

On the one hand, the Dihydrotestosterone article says: "DHT has been shown to be deactivated in skeletal muscle through the actions of 3-alpha hydroxysteroid dehydrogenase and therefore does not have a significant effect on muscle hypertrophy."

On the other hand, a scheme in "Medical Biochemistry" by J. Baynes and M.H. Dominczak says that DHT is responsible for mediating "anabolism, muscle mass". So, which is it that increases muscle size? Jack Daw 17:12, 26 July 2006 (UTC)

Endocrinology is pretty damn complicated. From my memory, DHT is a shorter-but-stronger-acting form of testosterone. That is, it has a great effect initially, but cells become less sensitive to it rapidly. Just because it does not mediate muscle hypertrophy does not mean that is is inactive in growing muscles, it may be implicated in myocyte recruitment (that is, if it doesnt make the muscle cells larger, it may make more of them). That said, there are many examples of paradoxical behavior in endocrine systems (steroid hormones, in particular). For example, the female sexual characteristics that are triggered on a whole body scale by estrogen, are sometimes locally mediated by DHT. It may be that under certain cicumstances and time-scales, DHT increases muscle mass, whereas under other conditions, it has a different effect. Tuckerekcut 15:22, 27 July 2006 (UTC)

odd water fowl seen on a trip to Tennessee

I have a picture of this wierd bird I saw on a river in Elizabethton, Tennessee, next to a covered bridge. I guess I cannot post it here. It was either a goose or duck. As big as a goose. White and black, with a red head. Very strange. I have never seen a bird like this. Does anyone know what it was? Thank you! Sue T.

Here is a duck with that coloring -- http://ohiodnr.com/wildlife/Images/diversity/Redheadlg.jpg, found on this Waterfowl Identification page. If you can post your picture at ImageShack or somewhere like that, you could then post a link here. --LarryMac 18:10, 26 July 2006 (UTC)

Muscovy Ducks are quite large for ducks, and would also fit.--Shantavira 18:25, 26 July 2006 (UTC)

about masturbation

hi all

is it good for health to have a regular masturbation practice......

Regular, yes. Obsessive, no. See the article. (we are, after all, an encyclopedia!) --LarryMac 19:21, 26 July 2006 (UTC)

Well, it's probably even healthier to have sex regularly, but life being what it is... --198.125.178.207 20:29, 26 July 2006 (UTC)

All considerations taken, I would have to say that masturbation is much healthier than sex, as a general rule.Tuckerekcut 15:13, 27 July 2006 (UTC)

Well, yes and no. You don't get much excercise masturbating, but on the other hand you don't get diseases either. I'd say it's a toss-up. Black Carrot 19:47, 27 July 2006 (UTC)

Of course it depends on what your masturbating with, stay clean. — The Mac Davis] ⌇☢ ญƛ. 20:16, 27 July 2006 (UTC)

oldest tv program

what is the date of the beginning of TV? programs? --207.42.222.108 19:58, 26 July 2006 (UTC)

Try starting with the article television. --Kainaw ^(talk) 20:02, 26 July 2006 (UTC)

The longest running TV show is, I believe, Meet the Press, which started airing in 1947. The longest running *syndicated* TV show is The Simpsons (syndicated means it is shown in rereuns. The news shows, for example, are never rerun). Raul654 20:02, 26 July 2006 (UTC)

The Daily Show is. Black Carrot 19:45, 27 July 2006 (UTC)

UV light through glass

I seem to remember having learned way back in high school that it's not possible to get a sunburn through glass, that the glass molecules are too close together to allow the right type of UV light to come through. My memory may be going or I just remember incorrectly, but nobody else has heard of this, or has heard the exact opposite. The Wikipedia entry on UV light says "Ordinary glass is partially transparent to UVA but is opaque to shorter wavelengths" and further that UVA light particularly "penetrates deeply and does not cause sunburn." Would I be correct in assuming that that means UVA will pass through, UVB and UVC will be blocked, so you can't be burned, but there can still be tissue damage and cancer development? Would the damage perhaps be worse than normal, since the body won't develop melanin, helping to block the rays out?

This figure (warning-it's a PDF) shows the absorbance of glass as a function of wavelength. (The type of glass isn't specified, but it's close enough for our purposes anyway.) As you can see, the glass absorbs very little light at wavelengths longer than 350 nm. This cutoff is smack in the middle of the UVA range (315 to 380 nm), so yes—a fair bit of UVA is still passing through the glass. For the shorter-wave UV, next to nothing will pass through unless you're using very bright UV illumination or very thin glass (A couple of millimeters of glass will reduce the UVB and UVC intensity by a factor of a thousand).

There's a good section on health effects in our article on ultraviolet. Briefly, all three types of ultraviolet light are energetic enough to damage skin proteins and cause wrinkles; the jury is still out, however, on whether or not UVA can cause DNA damage and skin cancer. TenOfAllTrades(talk) 22:54, 26 July 2006 (UTC)

I've done experimental work with deep UV lasers, and let me tell you it can be nauseatingly hard to get good optical elements that will work because ordinary glass is absolutely unusable. Incidentally, modern cars (at least in the US) are required to meet certain UV absorption standards for the glass they use so that people won't get burned driving long distances. I've been told many auto manufacturers actually greatly exceed the standards because it is easy to chooses glasses that very efficiently block UV. Dragons flight 23:18, 26 July 2006 (UTC)

Ooh cool, what materials do you have to use for UV optics? —Keenan Pepper 01:17, 27 July 2006 (UTC)

Speaking as a chemist, we use fused quartz in a variety of applications because it is extremely resistant to heat and most chemicals, and is transparent to UV down to about 170 nm. Sapphire is also used for some optical components (transparent down to about 250 nm) because of its high strength, hardness, and resistance to heat. TenOfAllTrades(talk) 02:35, 27 July 2006 (UTC)

Just curious, TenOfAllTrades, but are the sapphire ones really saphhire (like, blue...) or alumina?Tuckerekcut 15:10, 27 July 2006 (UTC)

Well, they're pure aluminum oxide in crystalline form, grown industrially in large ingots. The blue colour of natural sapphire (or ruby, which is mostly the same stuff) comes from trace metal impurities in the crystal; the optical grade stuff is colourless because it has a very low metal content. The industrial sapphire is like natural sapphire inasmuch as it's large, transparent, single crystals. For some applications, the sapphire is deliberately doped with metals to alter its optical properties; titanium:sapphire lasers, for instance, use ultrapure sapphire doped with a bit of titanium. For applications where colour isn't important, trace impurities are tolerated to a greater extent. I had to repair a high-pressure solvent pump that had little sapphire pistons; those ones were a pale greenish colour. TenOfAllTrades(talk) 16:03, 27 July 2006 (UTC)

Yeah, so ordinary glass absorbs most UVB and UVC radiation, but lets through UVA. This isn't a big deal when you are talking about blocking UV from sunlight because most UVA radiation is blocked by the Earth's atmosphere. In fact, glass blocks UV rays so well, that I recall needing to use special types of glass and plastic test tubes and petri dishes when working with bacteria in the lab which we planned on killing later with UV light. We had to pay a lot of extra money to make sure that the UV would penetrate the material with enough energy left over to kill the organisms inside. Indeed, I always have a little laugh when I am at the picture-framing store and the framer asks if I would like to purchase special glass to protect my pictures from UV light. Regular glass does quite nicely.Tuckerekcut 15:07, 27 July 2006 (UTC)