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Hello, There was a similar demo in the latest RI Christmas lectures -- a beaker containing apparently just liquid brought on for a member of the audience to dip his hand in. To his surprise, and the rest of the audience, he pulled out multiple frog spawn sized spheres -- invisible due to matched density. These were then dropped into another tank of liquid and disappeared again. Seemed to get a good audience reaction. On Fri, 2011-01-07 at 09:24 +0000, Chris Robbins wrote: > Dear Alessio, > > This is a nice demonstration and is part of the physical basis behind the H.G Wells story “The > Invisible Man” – see chapter 19: > > “And if you put a sheet of common white glass in water, still more if you put it in some denser > liquid than water, it would vanish almost altogether, because light passing from water to glass is > only slightly refracted or reflected or indeed affected in any way.” > > Of course by density he means optical density rather than mass density. This might be a good > starting point for a discussion on invisibility and how it might be possible scientifically. If you > were invisible in air how visible would you be in water? What about in different coloured light? What > would you need to do to make a non-transparent object invisible? Meta materials – here we come! > > Something else to consider is that because you can more easily see the test tube in some situations > then this means that light is being reflected/refracted and lost from the "direct line of sight". > This could introduce the idea of an optical coating on a lens to improve performance (your camera > lens will probably have a slight purple colour to it). I believe moths' eyes have antireflective > microstructures to achieve the same effect, although here it is to stop reflections giving them away > to predators. > > Kind regards > > Chris > > ------------------------------------------ > > Dr Chris Robbins > Why Learn That > Tel: 01663 749785 > email: [log in to unmask] > www.whylearnthat.co.uk > ------------------------------------------ > > > 23:04 > Thursday 06 January 2011 > > Hi All, > > This blog post shows a really cool demonstration on refractive index I have > > seen today. > > > > http://alessiobernardelli.wordpress.com/2011/01/06/refraction-index-magic/ > > > > <http://alessiobernardelli.wordpress.com/2011/01/06/refraction-index-magic/ > >>Please have a look and let me know what you think. > > Thanks, > > Alessio. > > > > > > Alessio Bernardelli > > > > IoP Network Coordinator > > 109 Maes Y Coed Rd > > Cardiff > > CF14 4HE > > > > Tel: 02920315988 > > Mobile: 07527528088 > > > > Blog: alessiobernardelli.wordpress.com > > Twitter: twitter.com/aso.ber > > > > ********************************************************************** > > Further information about the psci-com discussion list, including list > > archive, can be found at the list web site: > > http://www.jiscmail.ac.uk/lists/psci-com.html You may also change your > > settings and subscribe/unsubscribe to psci-com from the web site. > > > > Psci-com is part of the National Academic Mailing List Service, known as > > 'JISCMail'. 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