Wikipedia:Reference desk/Archives/Science/2013 July 18

= July 18 =

19th century medicine on sexual health
In the 19th century, how much onanism did a person have to practice in order to be considered medically an onanist or a person addicted to onanism? Are the physicians referring to masturbation or coitus interruptus or either one or both? Sneazy (talk) 00:55, 18 July 2013 (UTC)
 * A wise man once said: "Don't be a wanker!" DavidLeighEllis (talk) 01:02, 18 July 2013 (UTC)
 * On the lines of a classic definition of excessive drinking: more than the diagnosing physician. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:26, 18 July 2013 (UTC)
 * According to quintessential 19th century physicians such as John Harvey Kellogg, any masturbation was too much. DavidLeighEllis (talk) 15:40, 18 July 2013 (UTC)


 * You may find A Treatise on the Diseases Produced by Onanism by Samuel-Auguste Tissot (1728-1797) instructive (not current medical advice though). Also, the snappily titled Onanism, Spermatorrhoea : Porneio-kalogynomia-pathology : Boyhood's Perils and Manhood's Curse : An Earnest Appeal to the Young of America (1858) by Seth Pancoast MD. They don't write 'em like that any more. Alansplodge (talk) 21:22, 20 July 2013 (UTC)
 * Interesting that he uses "Pederasty" to refer to what we'd now call "zoophilia". Our article (Pederasty) doesn't countenance this meaning - is it Pancoast's personal idiosyncracy, or does our article require the historical usage to be expanded? Tevildo (talk) 19:12, 21 July 2013 (UTC)

Mental inheritance
Are traits like foolishness, psychotic thinking, awkwardness, laziness, aimlessness etc.. genetically inherited ?? — Preceding unsigned comment added by 103.15.60.174 (talk) 08:43, 18 July 2013 (UTC)


 * It rather depends on the causes of those traits. I suggest you read Biological inheritance.--Shantavira|feed me 10:36, 18 July 2013 (UTC)


 * I work with teenagers in high schools. I've been in a good cross section of schools. Many of these kids are what most adults would call lazy and aimless, and that's why many of the kids are lazy and aimless. It's very much a peer pressure thing. Those who show high commitment and effort are not conforming with the group ethic, and tend to be isolated from the bulk of students. So those traits for those students are definitely not inherited. HiLo48 (talk) 10:54, 18 July 2013 (UTC)
 * Nature versus nurture might be another good entry. As far as I can see, and I think this is quite interesting, very few things that matter between humans are mostly one or the other. For instance in HiLo48's observation many children do buck peer group pressure even with the consequences outlined. Dmcq (talk) 11:38, 18 July 2013 (UTC)


 * It's unlikely to be anything as simple as genetic inheritance - and even if there were genes for (say) "foolishness", I think it's impossible that all people who are foolish became foolish for genetic reasons. All of these attributes are likely to be the result of a complex interplay of many, many genes and wrapped up with how the person lived their early lives.  Note also that some traits such as poor education are passed down through a family even without genetics being involved.  Poorly educated parents are much less likely to read books to their children or even have books in the house - resulting in their kids being poorly educated too.  This is "inheritance" - but not through genetics.  But now consider a gene that might cause poor eyesight - if neither parents nor child can see well enough to read - then the child's education might suffer as a result - and then poor education would be inherited genetically but still entangled with environmental factors because with better technology the child could maybe listen to audio books and still get a good education despite a genetic problem.


 * All of these traits are going to be like that. A mix of genetic and environmental causes.


 * That said, there are conditions such as Asperger syndrome (which I happen to have) which frequently results in "awkwardness" in social situations and which is thought to have a strong genetic component. But we know that there are plenty of awkward people who don't have Asperger syndrome - so it's not correct to say that "awkwardness is always genetically inherited" - because it's clearly not.  But you also can't say "awkwardness is never genetically inherited" because we know that it sometimes is.


 * This is not a simple question. Your suggested symptoms are far too vague to be pinned to genetics or not-genetics.  I'd bet that every single one of those symptoms has some genetic component produced by many, many genes - and some nurture component produced by many, many issues during childhood and beyond.


 * Worse still, these are complex traits. I'm pretty foolish when it comes to investing money - but razor sharp when it comes to computer programming - do I have a "success-with-money" gene that's defective and a "success-with-computer-programming" gene that's working just great?  No.  That level of specificity simply isn't possible at the genetic level.  Humans only have 20,000 genes (according to Human genome) - there simply aren't enough of them for there to be such specific genes as a "foolishness-with-money" gene.  So that trait - even if it were 100% genetic - would come from a subtle blend of hundreds of genes.  Tracking down the effect of those genes to behavior with investments would be completely impossible.  Hence, there is unlikely to be a scientific answer to this question.
 * SteveBaker (talk) 13:30, 18 July 2013 (UTC)
 * Thank you everyone for your opinions! I want to ask whether these so called "genetic" components responsible for our personality and behavior be overcome manually ? — Preceding unsigned comment added by 103.15.60.174 (talk) 12:13, 20 July 2013 (UTC)
 * That's what people have said basically. It is like running, it has a genetic component but it only contributes a part to being a good runner. A person who practices running will most likely beat a person who has the genes of a champion but slobs in front of a television. Dmcq (talk) 14:21, 20 July 2013 (UTC)

Making oil from CO2
If we had enormous amounts of very cheap electricity, for example from nuclear fusion, would it be possible to produce oil (gasoline) from the CO2 in the air plus water (or whatever other byproduct is produced from burning oil), basically reversing the combustion reaction? I found the Synthetic fuel article but that's about converting stuff like coal or natural gas into oil, not CO2. 114.252.96.225 (talk) 13:34, 18 July 2013 (UTC)
 * Where is our article on reverse combustion? There are these folks who have worked on it. And some have spliced bacterial genes to do the work; Craig Venter mentioned in passing similar work in a TED talk. 88.112.41.6 (talk) 18:05, 18 July 2013 (UTC)
 * It's been discussed here a few times, I have found an article on the matter, but it's escaping me just now. CS Miller (talk) 19:30, 18 July 2013 (UTC)
 * The Sabatier reaction will produce methane from water and carbon dioxide (reverse burning). However, most hydrogen is commercially produced by the partial oxidation of methane, so unless you have a very cheap supply of electricity for the electrolysis of water, it's a non-starter. Once you have methane, you can then reverse-crack the methane to longer hydrocarbons (methane reformation). CS Miller (talk) 19:39, 18 July 2013 (UTC)
 * Plants and green algae do the job of converting CO2+light into plant matter - and there are several techniques out there to turn plant material back into hydrocarbons...not exactly oil or gasoline because those are very complex mixtures of chemicals - but certainly something you could run your car on. Normally, we'd expect to provide the light to the plants using sunlight - but if you truly had vast amounts of cheap electricity, then synthetic light might works out well.  You can read about this in our Algae fuel article. SteveBaker (talk) 19:30, 18 July 2013 (UTC)


 * One thing that has occurred to me is that Iceland has basically 100% of its energy from geothermal, but there hasn't been any way to export it. If Iceland could use the power to synthesize oil from simpler compounds, you might have something. Robert (talk) 20:28, 18 July 2013 (UTC)


 * Cellulosic_biofuel is all about taking CO2 and making something that can fuel a car. If you do it right, you can even make the whole process carbon negative, meaning that it would tend to reduce the concentration of CO2 in the atmosphere. Big companies like British Petroleum have invested heavily in researching this topic. SemanticMantis (talk) 21:49, 18 July 2013 (UTC)


 * 88.112.41.6's comment deserves a second mention. The first link refers to the recently patented device that catalytically converts carbon dioxide and water directly into hydrocarbons including octane. However, due to a lack in funding for further development, the device remains hopelessly inefficient. Plasmic Physics (talk) 23:23, 18 July 2013 (UTC)
 * Well, it's never going to be at a point where 100% of the energy you put into generating this fuel comes back out again when you burn it...that's just the laws of thermodynamics. So this is unlikely to be as efficient as (say) an electric car.  I doubt that it'll ever be as efficient as just electrolyzing the water to get hydrogen and using that in an internal combustion engine.  The business of consuming CO2 and that being useful in reversing global warming is a red herring - sure, you suck out CO2 - but then the exact same amount of CO2 comes right back when you burn the resulting fuel.  At best it can only be carbon-neutral.  It'll never be better for the environment than using pure electric or hydrogen-power.  SteveBaker (talk) 02:29, 19 July 2013 (UTC)


 * Just a few notes. I did not expect a hundred percent of energy consumed to be extracted, I'm also well aware of the thermodynamic laws; nor did I mention global warming. However, economics determines that as long as there is a demand, there is opportunity for supply -so it does not need to be more efficient than electric or hydrogen-powered cars, or what have you. Plasmic Physics (talk) 03:25, 19 July 2013 (UTC)
 * What about using photosynthesis to produce ordinary (hydrocarbon) biofuel, using a tiny fraction of that biofuel (or clean energy) to split hydrogen from carbon, and then burying the carbon? It would surely reduce atmospheric CO2, if an efficient reverse mining process is used to dispose of the carbon. I can see that it would lower the useful energy by essentially ignoring the carbon content of the fuel, but why is it not done? Is it too inefficient (because the carbon is either unused or still turned into atmospheric CO2) or just too expensive? 217.88.163.235 (talk) 07:51, 19 July 2013 (UTC)
 * That would be very inefficient and far too expensive to be viable on a large scale. The efficient way of using photosynthesis is to (a) grow woody plants, (b) turn them into charcoal by letting them dry and then heating them in the absence of oxygen, (c) bury the charcoal. Looie496 (talk) 15:16, 19 July 2013 (UTC)


 * Right now, just getting people to stop digging up the carbon that's already conveniently buried (we call that "coal") and turning it into CO2 would be a huge win! Until we can stop that from happening - we have no chance of getting carbon put back into the ground any faster than it's being dug up and burned.  If you have energy to spare then by far the best use of it is to provide electricity to the grid and thereby shut down some coal-fired power stations (we're still building MORE of those horrible places!!).  Doing that is much *MUCH* easier than sequestering the carbon after it's been turned in to CO2!  If sequestration is to provide any net benefit at all, it has to be sequestration of the carbon dioxide itself...and we have no good ways to do that.  In a future world where CO2 production has been essentially shut off using nuclear, fusion, wind, solar, wave, etc energy - then trying to use some of the spare energy we happen to have just lying around to pull CO2 out of the air might make sense.  However, growing large forests over the sahara desert, sustainably harvesting the timber, converting it to charcoal and burying it in disused coal mines is probably the most efficient way to sequester CO2. SteveBaker (talk) 15:14, 19 July 2013 (UTC)


 * I don't agree that "we have no chance of getting carbon put back into the ground any faster than it's being dug up and burned". We are currently injecting around ten billion tons of carbon into the atmosphere per year.  I estimate that we could actively remove that much carbon at a cost on the order of $1 trillion per year.  Obviously that's a lot of money, but it is only around 1% of the world GDP.  We could do it if we were motivated enough. Looie496 (talk) 14:56, 20 July 2013 (UTC)
 * on the $1 trillion number! 105.236.218.126 (talk) 23:01, 20 July 2013 (UTC)


 * My near term non biological solution: CO2 scrubber -> Sabatier reaction (you could stop here if you like methane) -> Steam reforming -> Fischer–Tropsch process Its probably inefficient but some reaction is exothermic, you could funnel them to the endothermic ones and use a lot of energy and heat to drive it — Preceding unsigned comment added by 140.0.229.26 (talk) 11:24, 20 July 2013 (UTC)

Optimal watering schedule
I recently installed drip irrigation in my vegetable garden and realized that my home's existing lawn irrigation controller wasn't advanced enough to handle seperate schedudules for the lawn and garden. I went overboard replaced it with an industrial controller from the scrap bin where I work. :-) I have it wired up to control the zones, and have the flexibility to schedule it based on pretty much anything. Right now I have it set up so that it can schedule zones based on the sunrise time. I have plenty of inputs to talk to pretty much any sort of sensor you can imagine, but I don't want to spend much. I will attach a thermocouple for measuring the air temperature, and I'll probably at least pick up a cheap rain sensor - they're designed to automatically cut power to sprinkler solenoids for a period after rain, but I can set one up so that the controller knows it rained and can act on that information in any way I want it to.

I live about 1000 ft from Lake Michigan near Holland, MI and have about 6 inches of top soil on top of sand. My front lawn is full sun, and the back is shaded for about half the day. The lawns use impact sprinklers, except for sprayers in some small sections. The garden is raised beds with 6-12" of a 50/50 topsoil/compost mix. The sun varies depending on the bed, but (for now) all the beds are on the same drip irrigation zone.

I'm looking for guidelines on the optimal way to schedule my sprinkler systems to reduce water use. I'll appreciate advice from personal experience, but I would really prefer reliable sources that have information applicable to my region and soil. I'd let the lawn go brown in the summer, but my retired neighbors are meticulous about keeping their lawns perfect, and my kids would probably prefer to play in soft grass anyways. If I do it right, I'm hoping that I can add a maple tree in the front lawn without it growing floating roots. I also plan on adding fruit trees and blueberries to my garden next year, but I can set those up on another irrigation zone if I need to. 209.131.76.183 (talk) 14:02, 18 July 2013 (UTC)


 * Here's some nice info from the MSU extension service (in the US, these are great resources!), . They have links to calculators, and discuss best practices. Of note, frequent (e.g. daily) light watering is bad for turfgrass. Also, don't sprinkle on your trees, use a soaker hose or Drip_irrigation to get water down deep. SemanticMantis (talk) 14:18, 18 July 2013 (UTC)
 * You may also be interested in xeriscaping, even though you're not exactly in a dessert. If your soil is that sandy and dry, you might be able to save water with something slightly odd for your area, like bermuda grass. FYI, the extension service will probably also answer specific emailed questions. They are actual experts, try them out :) SemanticMantis (talk) 01:06, 19 July 2013 (UTC)
 * Anything that involves swapping out my whole lawn is going to be too expensive for now, but I'll keep it in mind. If it were up to me, the whole neighboorhood would be a native habitat - either sand and uncut dune grass with the occasional Pitcher's thistle, or woodlands with sensibly-maintained underbrush. I'll contact the extension service about lawn ideas - they may be able to suggest some native species that will do well as an alternative turf. I'll also have to research township rules in that case. Thanks! 209.131.76.183 (talk) 12:18, 19 July 2013 (UTC)
 * Here in Austin, TX, we're in the middle of a multi-year drought. Unfortunately, local home-owner's associations (HOA's) are in pretty much every neigbourhood and require residents to have grass and typically dictate how tall the grass is allowed to be and bitch at you if it turns brown (which native texan grasses are quite happy to do - and recover from the next time it rains).  Just a few days ago, the city passed a law requiring HOA's to allow xeriscaping - and I'm hopeful that we'll be able to shift to the kind of look you see for the desert homes out in Arizona - earth tones, xeriscape - zero water environments, that kind of thing.  Throwing water that's carefully purified to be good enough for human consumption onto grass to make it grow so you have to get out in 100 degree temperatures to cut the stuff sure gets old fast! 15:53, 19 July 2013 (UTC)
 * My water comes from a well, and I assume that the aquifer gets recharged pretty well from Lake Michigan, but it still seems like a waste. I don't use fertilizer or pesticides on my lawn, but my neighbors definitely do, and I hate the thought of any of that getting into the runoff. We don't have an HOA anymore, but I still have to make sure to follow township rules. I put off sprinkling as long as possible this year, and maybe 10-20% of the grass went dormant and the green stuff is growing really slowly. We've had a 90-100 degree heat wave for at least a week now, but I haven't had to mow in it. 209.131.76.183 (talk) 16:46, 19 July 2013 (UTC)

This is the OP on a different IP. I heard back from the extension service already, so I figured I would follow up with their advice. They recommend placing small containers around the lawn to get an idea of what rate the water is accumulating as the sprinklers run. Then time how long it takes until there is ponding or run-off - that's how long the sprinklers should run at a time for optimal watering. Calculate how long the sprinklers need to run to deposit an inch of water (the weekly target), and divide it by the time it takes to pool/run to figure out how many times to run the sprinklers in a week. Irrigation should run in the morning, but a short afternoon burst can also help cool down the turf. If there is rain, just take that into account as part of the 1 inch per week. He also gave a link to a drip system calculator for my garden, but all it does is determine flow rate, which I already know (assuming the numbers on the packaging are correct). I'm not as worried about that one anyways - the packaging had suggested schedules, and it is easy to check the soil in the raised beds to see how well it is working. He gave these links for native landscaping in Michigan: .108.194.140.240 (talk) 11:38, 20 July 2013 (UTC)

Is the gravitational lensing caused by Earth measurable?
In theory, couldn't one measure terrestrial lensing of stars or sunlight from a tall tower or airship? I'm thinking something like 50+ miles of viewing radius should provide sufficient enough angle with the horizon to measure such effects, comparing the deflection angles of various wavelengths or some such. Have any experiments of this sort ever been attempted? 70.112.97.77 (talk) 14:39, 18 July 2013 (UTC)
 * Someone here who knows the math better can probably figure out just how much of an effect to expect, but I know it is going to be very very small. I expect that distortion from the atmosphere will be much greater than what you're proposing measuring. 209.131.76.183 (talk) 14:48, 18 July 2013 (UTC)


 * When it comes to gravitational lensing, I've seen a lot more mathematical theory than actual observational data. This leads me to the dismal opinion that many publications about gravitational lensing are actually very well-camouflaged professional pseudoscience; they typically consist of very pure and even correct mathematics, but this isn't science when there's almost no physical data to validate specific claims.  A few landmark observations of the lensing effect do exist, which provides a little bit of confidence that the general concept is valid; but the famous examples are all very faint deep sky objects, and most of the effects are small perturbations due to massive black holes.
 * I do not believe any well-known experiment has ever sought to measure gravitational lensing deflection of light due to Earth's gravity. In fact, even deflection effects of the much larger Sun's gravitation are contentious due to the tiny magnitude of the effect and the impact of other experimental error.  You will unfortunately find that our article, gravitational lensing formalism, references mostly self-published arXiv pre-prints, rather than peer-reviewed science.  Our much better main article, gravitational lensing, lists several famous historical examples, like the Einstein Cross, where the effect and its theory are much better supported by the data.  Nimur (talk) 15:21, 18 July 2013 (UTC)
 * The amount of deflection due to gravitational lensing is
 * $$\theta = \frac{4GM}{rc^2}$$.
 * If you plug the Earth's mass and radius into that equation, you get θ=3x10-9 radians, which is about half a milliarcsecond. It's not uncommon for astronomers to deal with angles that small.  Red Act (talk) 15:41, 18 July 2013 (UTC)
 * For the sake of clarity, I edited my post. Gravitational lensing and deflection of light by gravity are both due to the exact same physics; but astronomers really only use the term "lensing" when the deflection is large enough that the gravity causes light to behave similarly to light passing through a refractive lens.  This is probably another reason why you won't find much when you search for "gravitational lensing" by small planet-sized masses - even if the effect exists and is measurable, it isn't lens-like.  Nimur (talk) 15:50, 18 July 2013 (UTC)


 * It looks like my statement above that dealing with an angle of a half a milliarcsecond wouldn't be uncommon for an astronomer was a bit optimistic. I was thrown by knowing that the Gaia space observatory that will be launched this coming October is hoped to measure star positions down to 20 microarcseconds or less.  However, ground-based telescopes can only resolve things down to a few hundred milliarcseconds due to atmospheric effects, and even space telescopes like the Hubble which avoid those atmospheric effects are diffraction limited to dealing with angles of about 100 milliarcseconds.  Some advanced observatories have been starting to use adaptive optics to get resolutions down to about 50 milliarcseconds, but Gaia's dealing with angles smaller than a milliarcsecond will be quite a breakthrough. In comparison, the gravitational deflection of light by the sun as was measured by Eddington is about 1.75 arcseconds, which is much easier to measure than a half a milliarcsecond.  Red Act (talk) 21:30, 18 July 2013 (UTC)

Interesting, thanks all! 70.112.97.77 (talk) 19:59, 18 July 2013 (UTC)

Earth sized planets are routinely detected via gravitational microlensing. Count Iblis (talk) 23:05, 19 July 2013 (UTC)
 * Yes, and such a clever technique too - amazing that it even works! 70.112.97.77 (talk) 06:41, 20 July 2013 (UTC)

Is it an example of precipitate reaction?
Here is a simple reaction- Fe + CuSO4 > FeSO4 + Cu Is this an example of precipitate reaction? If yes, then which one is precipitate? Publisher54321 (talk) 15:45, 18 July 2013 (UTC)
 * Cu (s) for most sulfates dissolve in solution, except barium or lead sulfates. 140.254.227.57 (talk) 15:48, 18 July 2013 (UTC)
 * No, it is not strictly a precipitation reaction. It can be classified a number of ways, either as a single replacement reaction or as a redox reaction.  Precipitation reactions are usually a subcategory of reactions known as double replacement reactions.  Classic precipitation reactions involve the mixing of two salt solutions to produce an insoluble salt.  Typically, these are reactions like sodium chloride solution mixing with silver nitrate solution (producing silver chloride as a precipitate) or potassium sulfate solution mixing with barium nitrate solution (producing barium sulfate).  -- Jayron  32  16:47, 18 July 2013 (UTC)

Correlation between continuous visible spectrum and the models used in display/detection of red, green, and blue channels
When dealing with color from the point of view of digital monitors, cameras, and so forth we talk about the differing intensity levels of red, green, and blue to describe the perception of the multitude of colors. But in examination of the electromagnetic spectrum of visible light we instead consider a well-defined bandwidth of frequencies with NO regard for intensity. What is the mathematical relationship of these two models? And how does a "pure" signal (peak frequency) of say yellow light "stimulate" intensity levels of red, green, and blue within the eye and optical detectors in the first place? 70.112.97.77 (talk) 15:58, 18 July 2013 (UTC)


 * I have no idea what the second sentence of your question means; this "we" of whom you speak is considering wrongly. The colour vision article shows the response curves for the three types of colour sensing cone cell found in the human eye, which are non-uniform and which overlap. The arrangement is broadly similar in the CCD detectors found in digital cameras, albeit with different curves. -- Finlay McWalterჷTalk 16:08, 18 July 2013 (UTC)


 * The electromagnetic spectrum of visible light pertains to the wavelength at which the light emits. Color itself is the product of our perception, created by our visual pigments in the retina, and is combined from wavelength by the electromagnetic spectrum of visible light, intensity (how bright/dim the color is) and saturation (how much whiteness a color has). According to Hering's theory of color vision, there are three mechanisms, each of which responds in opposite ways to different intensities or wavelengths of light. The Black (-) and White (+) mechanism responds positively to white light and negatively to the absence of light. Red (+) Green (-) responds positively to red light and negatively to green, and Blue (-) Yellow (+) responds negatively to blue but positively to yellow. So, an object that reflects light at the peak wavelength of yellow light may react with the color receptors to fatigue, so that when the color is gone, the opposing color - less fatigued color - appears as an afterimage. The intensity, wavelength, and saturation are in the environment, not created in the eye. We just perceive them a certain way, giving them special characteristics. Sneazy (talk) 16:32, 18 July 2013 (UTC)


 * To correct our OP a little here - when you get a description of color using the visible spectrum, you still need intensity data. Generally, what you have is a plot of frequency versus intensity.  Converting that into an RGB representation entails looking at the frequency response of the Red, Green and Blue sensors and using that to produce a weighted sum of the spectral data under each of the three curves.  The reverse operation is impossible - there is insufficient information in the R/G/B intensities to reconstruct the original frequencies unambiguously. SteveBaker (talk) 19:22, 18 July 2013 (UTC)

Thanks for the responses. I still don't get it though: Yellow light has a frequency of 525–505 THz. Red, green, and blue range from 480–400 THz, 575–525 THz, and 670–610 THz respectively. How exactly does varying the intensities of RGB on a display produce what appears to the human eye as a frequency that lies outside the range of these three primary colors (eg: yellow at 525–505 THz)? 70.112.97.77 (talk) 19:53, 18 July 2013 (UTC)


 * I believe that would depend on the source of the light. Color may be combined together by shining two or more colored lights or mixing two or more colored paints. The former method, shining two or more colored lights, will produce an additive color mixture - all lights are bounced from the wall and into your eye. The latter method, mixing paints, will produce a subtractive color mixture. If a paint reflects long and medium wavelengths and a paint reflects medium and short wavelengths, and you mix them together, they will superimpose on each other, absorbing both long and short wavelength visible light, and therefore you may be left with green - a medium wavelength light. Display screens are just displays of light, not paint. The colors are "mixed" together to create the vast array of colors we see. I put "mixed" in quotes, because display screens have pixels. It is our brains that create the illusion that we are seeing "mixed lights". Think pointillism. Sneazy (talk) 20:47, 18 July 2013 (UTC)


 * (This is a pet subject of mine!)


 * The curious thing about "yellow" is that there are two completely different waveforms that both look "yellow" to our eyes and to our cameras - but which are in fact totally different colors when examined spectroscopically. Consider light from a sodium light - which is pretty much entirely composed of light whose frequency is intermediate between red and green.  There is no red or green frequencies coming from that lamp at all.  Then consider the IDENTICAL-LOOKING light from a TV screen that's showing a picture of a sodium light - which is a mixture of pure red and pure green light with no frequencies in the "yellow" range whatever (because a TV has no means to generate light of the frequencies that the sodium lamp produces)!


 * Our eyes and our TV cameras simply cannot distinguish between these very different waveforms. They look exactly the same shade of yellow - yet they are in no way similar if examined spectrographically.


 * I like to think about someone who is colorblind and unable to see green light directly. For those people, the frequency of light midway between red and blue looks identical to a mixture of red and blue...put another way, green and magenta look the same to those people.  Well, that says to me that "sodium-lamp-yellow" and "TV-picture-of-sodium-lamp-yellow" are as different as green and magenta...but our eyes can't tell!


 * If you are unconvinced, try to find a very old orange-colored sodium street lamp and view it's light on a dark night through a prism - or (since you probably don't have one) reflected in a CD-ROM disk. The CD-ROM breaks light up into it's component frequencies like a prism or spectrograph - and all you see is a single patch of yellow light.  Now go to your computer screen and set the whole screen to a yellowish orange and in a darkened room, view it the exact same way.  When you do that, there is no yellow light reflected on the CD-ROM - only separate patches of red and green.


 * It's interesting to note that some animals have more than three color receptors - goldfish and some freshwater shrimp actually have a proper yellow receptor in their eyes. They must see sodium lamps and pictures of sodium lamps as wildly different colors...as different as green and magenta in fact!
 * SteveBaker (talk) 01:59, 19 July 2013 (UTC)


 * Sorry, I somehow overlooked your response. It makes a lot more sense now. Thanks! 70.112.97.77 (talk) 05:21, 19 July 2013 (UTC)


 * Steve, every time a question about color vision comes up you post in it, and every time you're wrong and someone has to correct you. Please stop.
 * The frequency spectrum of RGB subpixels varies widely across displays, but generally there is significant output at the 589nm wavelength of a sodium-vapor lamp, and on plenty of displays (like these) will produce as much yellow as red or green light when displaying an approximation of a sodium lamp's output. Also, the human eye can tell the difference, since the RGB display's approximation of the color is visibly desaturated (mixed with white). -- BenRG (talk) 19:24, 19 July 2013 (UTC)

I just thought of something. Consider, for simplicity's sake, three pure sinusoids of specific frequency. Varying the magnitude component any of these might produce a resulting waveform that is a very close approximation some other, non-related frequency (or frequencies). Could this be what is happening when one views a pixel for instance? Up close, distinct bands of red, green, and blue of varying intensity; from afar, an interference pattern that "fits closely" to the shape of say a yellow waveform? 70.112.97.77 (talk) 21:33, 18 July 2013 (UTC)


 * Amplitude and frequency are two separate things. Amplitude describes "how big" the wave is, and frequency describes "how frequent" the waves come in a period of time. If you change the amplitude, then you just change the size of the wave from hill to trough, not how frequent the waves come in a period of time. That said, the RGB on a display screen is made up of RGB pixels. The reason why we see a wide range of colors on the display screen is that these pixels are extremely tiny, and like pointillism, our brains perceive them as blending together to create various colors of the spectrum. The perception of various colors is real, even though all the colors of the spectrum are not in the pixels. Sneazy (talk) 22:48, 18 July 2013 (UTC)

Well, what I meant was that in varying the amplitude (or even phase) of a single sine wave which is being combined with several other (unchanging) sinusoids, one finds that certain values can actually "deform" the result so dramatically that if one were to say pass it through some sort of smoothing function or whatnot (the "fuzzy logic" of the human brain, for example) one might obtain a waveform that "somehow appears" to contain frequencies not present in the original signal. Seems plausible to me, but then again, maybe I'm way off here... 70.112.97.77 (talk) 04:30, 19 July 2013 (UTC)
 * No, it doesn't work like that. The three cone types in the eye are all sensitive to a wide, overlapping range of frequencies, and the three phosphor types of an RGB display produce a wide range of frequencies. Since all visible wavelengths are present in the image and all visible wavelengths are detected by your eye, there's no problem of seeing frequencies that aren't there. The three cone types are called L, M, and S, and it's a mistake to think of them as "R, G, and B", since that's not what they detect. The three phosphors on a display are red, green and blue in the psychological sense: they are defined by how they stimulate the cones in the eye of someone with normal color vision, not by their physical spectrum (which varies hugely from one display type to another).
 * When you look up close at a grid of R and G subpixels, cones in different patches of your retina are being stimulated in different ratios: L more than M in the R regions and M more than L in the G regions (but significant amounts of L and M stimulation in both). When you're farther away, all the cones are getting light from the R and G subpixels, so they are getting the average of the two, which is closer to equal in L and M. These relative ratios translate into psychological red, green, and yellow respectively via the opponent process. -- BenRG (talk) 19:24, 19 July 2013 (UTC)



One doesn't need to be a goldfish to see the difference between an actual sodium flame and this picture. The article Gamut explains that no tricolor image can duplicate any of the spectral colours. It's depressing when someone who knows better still exploits the protected forum of the reference desks to promote a spelling deviation that they would find unacceptable in Wikipedia articles. Human vision has evolved its (not "it is") responses to work with the incoherent solar light that is broadband radiation. The retinal cones effectively measure power not phase, and colour sensations do not arise from any particular waveshape. DreadRed (talk) 23:11, 19 July 2013 (UTC)
 * Interestingly, we have two completely disjunct articles on the subject; Opponent process and Color_constancy Gzuckier (talk) 08:05, 22 July 2013 (UTC)

If Feverfew is poisonous to animal pets
Area Essex England. Is the Feverfew plant poisonous to animal pets? — Preceding unsigned comment added by 80.47.214.143 (talk) 18:47, 18 July 2013 (UTC)


 * It is not. The Eurasian variety described here is harmless to animals except in large doses; I'm guessing withdrawal symptoms would be similar. The North American variety (parthenium) is toxic to various animals, but you almost certainly have the Eurasian type in Britain. Robert (talk) 20:34, 18 July 2013 (UTC)


 * Careful, I think this may fall under the category of medical advice with some assumptions thrown in for good measure. — Preceding unsigned comment added by 122.111.254.165 (talk) 03:12, 19 July 2013 (UTC)
 * Yes, this information would go to a licensed professional in most jurisdictions. μηδείς (talk) 03:36, 19 July 2013 (UTC)


 * Rules Q: Is "Licensed" advice a valid WP:rule? I only see that neither "medical" nor "legal" advice is to be given. A question if a certain plant is poisonous to pets is neither (veterinary if any).
 * Can an admin please review this one? 217.255.150.14 (talk) 07:58, 19 July 2013 (UTC) (Not the topic starter.)
 * We are not supposed to give professional advice, such as medical or legal advice. Click on disclaimer at the bottom of this page: "Not professional advice--If you need specific advice (for example, medical, legal, financial or risk management) please seek a professional who is licensed or knowledgeable in that area."  We certainly shouldn't be telling an OP that a plant we cannot see and are not qualified to identify will not poison his pets. μηδείς (talk) 17:08, 19 July 2013 (UTC)
 * This "ethics" nonsense is a disease. Wouldn't we answer a question about whether benzene is toxic?  To humans, that is?  Then give sourced data here and move on.  If you insist, you can explain you're not giving this information with the intention that somebody is going to feed his cat this herb, not that there's any indication that was the plan. Wnt (talk) 18:58, 19 July 2013 (UTC)
 * I should note that searching PubMed wasn't very productive for me this time - it yielded up a review of moderate quality which says that its chronic toxicity hasn't been tested, and that the immediate adverse reactions can include mouth ulceration and dermatitis in humans.  I didn't find anything about "feverfew" and "dog" or "cat".  There is mouse work available, some of which indicates beneficial effect, but extrapolating from those to a more common pet would be as dicey as extrapolating to or from humans.  Checking Google Scholar yielded an alleged search hit  - it doesn't look very scientific and I have no idea how to get to the part that actually says "feverfew" without reading as much of it as Google cares to serve and see if it's in there somewhere.  Ditto, probably others. Wnt (talk) 19:42, 19 July 2013 (UTC)
 * So, you know that the OP hasn't got American feverfew, and his pets are not rabbits or ponies, Wnt? What is this burning hit-the-crackpipe itch to give half baked and potentially dangerous advice to all comers?  We simply cannot answer the OP's question. μηδείς (talk) 01:14, 20 July 2013 (UTC)
 * It's IP, not OP.
 * The policy (if the disclaimer counts as one) is at best ill-worded. "If you need specific advice..." is way too broad - it would cover many of legitimate questions - especially the really well-thought and well-stated ones.
 * Surely we can tell IP 80 if feverfew is poisonous or not. The replies as I see them are good, valid answers: American is different from Eurasian, and different pets react differently. For example, dogs can (usually) be treated with human medication, while cats cannot. Their chemistry is so different that most medicine does more harm than good. 217.255.175.134 (talk) 05:55, 22 July 2013 (UTC)

longest-running experiment to reach an unknown conclusion?
So, pretty simple. An experiment can be done where by the time the results are in, nobody knows for sure what these results will be: hence the experiment.

What is the longest such experiment (days/months/years/decades/whatever) that was not simply a demonstration but a genuine experiment? (i.e. specific example). Or, if not the longest, then some candidates for that title. Thanks! 178.48.114.143 (talk) 19:28, 18 July 2013 (UTC)


 * The Pitch drop experiment is well-known. That article also links to Long-term experiment. 209.131.76.183 (talk) 19:57, 18 July 2013 (UTC)


 * There has been a very long running test of evolution with bacteria: E. coli long-term evolution experiment - it's been running for 25 years now - but, again, I think the outcome was pretty much expected at the outset =. One thing though - an experiment of such scale that doesn't produce any surprises is still an important experiment...it might have shown up something surprising.  Nobody knew.


 * My vote for longest running experiment with unknown results is the Voyager 1 and Voyager 2 missions (Voyager 2 has been up there longer). It's essentially a range of science experiments - a part of which was to ask what we would measure with it's instruments as it left the solar system.  I believe the magnetometer experiment was the first to be activated of the half dozen instruments that are still functioning.  Certainly the results it's been producing have been totally unexpected.  It launched in 1977 - so 26 years or so - which handily beats the E. coli thing. SteveBaker (talk) 01:44, 19 July 2013 (UTC)


 * The Domesticated_silver_fox experiment has no known conclusion, and was started in 1959. SemanticMantis (talk) 02:29, 19 July 2013 (UTC)
 * Oh! Well played!  Yes, I forgot about that one...it's an absolute classic - we have a new winner! SteveBaker (talk) 03:27, 19 July 2013 (UTC)
 * How is that the winner when the pitch-drop experiment outdoes it by 32 years? Also, I am fairly certain there was a break in the continuity of the Silver Fox experiment around the fall of the wall. μηδείς (talk) 03:32, 19 July 2013 (UTC)
 * Because the OP specifies an experiment with an "unknown conclusion". There is nothing whatever unknown, surprising or unexpected about a pitch-drop experiment.  Even if there were, the results were well-known after the first or second drop - which happen about every 10 or 11 years - and would give us some idea of a number for the viscosity of pitch.  At this point (after 8 drops) it's a cool demonstration - but could hardly be described as an "experiment". SteveBaker (talk) 14:34, 19 July 2013 (UTC)


 * But a short-lived victory because... SteveBaker (talk) 03:34, 19 July 2013 (UTC)
 * I found the Park Grass Experiment has been running since 1856 investigating crop yields and such. Any advance on that? SteveBaker (talk) 03:34, 19 July 2013 (UTC)
 * Probably. The Morrow_Plots were established soon after, and they are still often used for current research (though there are only a few hundred m^2 left of the original experiement). The Park grass and other stuff at the Rothamsted_Experimental_Station is probably the oldest broadly defined, relatively continuously running extant "experiment". The Oxford Electric Bell is probably more of a "demonstration" in the OP's terms, and it did miss a few days here and there. SemanticMantis (talk) 04:24, 19 July 2013 (UTC)
 * Yeah - I discounted the bell - it's a demonstration - and nothing unexpected is ever likely to come from it. SteveBaker (talk) 14:34, 19 July 2013 (UTC)
 * Incidentally, there's recently been some hot news in a Dublin version of the pitch drop experiment. HenryFlower 03:43, 19 July 2013 (UTC)


 * There are some fun writeups on all of these (and some others that do not beat the Park Grass record - which this source credits to 1843) here: National Geographic, Atlas Obscura. The one for Vesuvius monitoring goes back to 1841, though I'm not sure that's an experiment, even though the outcome is indeed unpredictable so far. 174.88.9.124 (talk) 17:31, 19 July 2013 (UTC)


 * Professor William Beal started an experiment 134 years ago in 1879 which is still going on and providing data at Michigan State University. He buried seeds in dry sand in glass jars 20 inches below grade to study the percent germination of the seeds over time. Each of 20 glass jars contained 50 seeds from various plants, and he arranged for his successors to continue the experiment after his demise by digging them up and planting them every so many years. An article from 2000 said "The Beal experiment represents the oldest continuing experiment at the nation's oldest college of agriculture." In 2000 only "Verbascum blattaria, a weed commonly called moth mullein." sprouted, according the the linked publication, but elsewhere it said 2 seeds sprouted. Perhaps they were they same species.  The next jar will presumably be opened in 2020. At the present pace of opening jars, the experiment will continue until 2100, for a duration of 221 years. See, .  According to , the Beal experiment is the oldest ongoing one. According the the last publication, Auburn University has been running a crop rotation experiment since 1896. As was mentioned above, the University of Illinois has been running their own agriculture experiment for a long time, the Morrow Plots. which grow corn in one plot of ground every year without crop rotation or fertilization, producing poor quality stunted corn, compared to higher yields in plots with crop rotation and fertilization. It has been an ongoing experiment since 1876.  Maybe U of I is considered to have begun new experiments when the conditions changed for the high yield plots. Edison (talk) 18:24, 19 July 2013 (UTC)
 * Cool, I was not aware of the Beal germination experiments. UI Morrow plots could be ruled out on many technicalities, but I think the main reason is because only 3 of the 10 original plots are left (more info and pictures here [agronomyday.cropsci.illinois.edu/2001/morrow-plots/]). So, although the current plots have been studied since 1876, a purist (or a MSU rival ;) could say the original experiment ended when the first plot was removed. But now I'm wondering why NPR ruled out the Park Grass... SemanticMantis (talk) 19:00, 19 July 2013 (UTC)


 * 'longest-running experiment to reach an unknown conclusion?'
 * Are we talking about those experiments undertaken by the modern scientific method or in the wider sense of experiments that lead to discovery and new understandings?
 * Archaeologists might disagree on when mankind first learnt how to control fire yet NASA and many other organisations are still furthering this form of rapid oxidisation experiment to this very day – because they still don't have all the answers.Some primates have been found to be tool users but non so far have been observed   preparing  a really nice medium rare stake with French fries and sauteed mushrooms.--Aspro (talk) 22:41, 19 July 2013 (UTC)


 * Here we got a historical sample of primates preparing a nice medium rare stake with a French fry: Stilke Hermann Anton - Joan of Arc's Death at the Stake.jpg --Cookatoo.ergo.ZooM (talk) 22:27, 20 July 2013 (UTC)


 * Well, we have everything from Human impact on the environment to Intelligent primates who use language if you want to get out of the professional scientist world. Gzuckier (talk) 08:10, 22 July 2013 (UTC)

Laser Magnet
Magnetic fields normally affect their entire surroundings, but it there a way (in today's technology or in theory) to fire a magnetic field at a specific direction, similarly to how lasers emit light? Something that would enable, for instance, to pull a spoon but not a fork that lies next to it. Thanks, 84.109.248.221 (talk) 20:06, 18 July 2013 (UTC)


 * See this URL: http://www.mushield.com/faq.shtml#q1 . To me, it looks like you couldn't direct the whole force of a magnet in one direction, but if you surrounded the whole thing except for a small gap with shielding material, it would warp the field so it only stuck out the gap. However, apparently magnets can't be shielded from one another. That's as far as I understand what this says. Robert (talk) 20:39, 18 July 2013 (UTC)


 * Wasn't this question asked and answered on July 5? Nimur (talk) 00:08, 19 July 2013 (UTC)
 * Good answer there at your link, but now I'm thinking of asking a new question about collimated vs. coherent light :) SemanticMantis (talk) 01:11, 19 July 2013 (UTC)
 * The short answer is no.


 * I'm taking your question to be a question purely about magnetostatics, since your question only mentions a magnetic field, not an electric field, and if you wanted to consider electromagnetic fields in general, then a laser beam would be the obvious example of an electromagnetic field that's in the form of a beam like a laser beam.


 * In magnetostatics, no matter what configuration of magnets and objects of various permeability and susceptibility there are in a system, at large distances the magnetic vector potential due to the system can be written as a multipole expansion which consists of a series of terms which drop off with distance as 1/rn. The smallest n that can have a nonzero term in the multipole expansion is n=2, i.e., the term for the magnetic dipole moment.  A magnetic monopole, which would drop off as 1/r, is sometimes theorized to exist, but is not known to exist, much less a term that drops off as 1/r0, i.e. a term for a contribution to the field which remains constant independent of distance, like how the intensity of an ideal laser beam is independent of distance from the source. And the magnetic field can't even drop off as 1/rn for some n>=2 but still at least be in the form of a cylinder pointing away from the source (a beam), because that would violate the conservation of magnetic flux (the divergence of B is zero).  So there's no such thing as a static magnetic field in the shape of a cylindrical beam.  Static magnetic fields always spread out with distance.  Red Act (talk) 01:35, 19 July 2013 (UTC)
 * IMO, lasers are by definition electromagnetic, not magnetic, emitters. However, some amount of "magnetic lensing" is both possible and in use (iron cores, read/write heads of hard disk drives, etc). The July 5 entry has more links on this. 217.255.152.44 (talk) 08:07, 19 July 2013 (UTC)
 * A magnetic field that's in the middle of an iron core or is a couple microns away from a hard drive head is a lot different from a magnetic beam extending a sizeable distance from the source through air, which is what I read the OP as asking about. The fork and spoon in the OP's example aren't in the middle of an iron core, and simply putting a magnet right next to the spoon isn't what the OP is asking about, either.  Red Act (talk) 15:18, 19 July 2013 (UTC)


 * I am sorry, why does the question make me think of sharks and pinkies? μηδείς (talk) 01:09, 20 July 2013 (UTC)
 * Left claw north - right claw south! Tevildo (talk) 23:13, 20 July 2013 (UTC)