> > > > In other words, for the Invisible Man to be transparent while in air by the usual rules of physics, he'd have to be no more complicated than a giant single-celled amoeba. He'd only become mostly "invisible" if he took this amoeba form and hid inside water. :-)
> > >
> > > Well thats the point. Water isn't invisible, it is transparent. The Invisible Man isn't transparent (which is partialy visible at the edges) he is invisible, meaning he breaks the true laws of physics.
> > >
> > > Speed'deffinitionsareeverythinginSci-Fi'ball
>
> Hmpf. You missed my point entirely, Joseph. For example, let's consider that air has an index of refraction of 1.002, and water is 1.333, and the Amazing Amoeba Man (theoretically) has a refractive index of 1.370 along his boundaries. So if you put Amoeba Man in water, he durn well becomes well-nigh *invisible* in that environment because the change in refractivity between himself and water is only 0.037. Compare that to the 0.368 between himself and air, which would render him *transparent* in air but not invisible.
>
> I was merely speaking of circumstances in which an Invisible Man COULD conceivably become invisible, that is, if he were a man-sized amoeba. It is more entertaining to deal with the conceivable in SF rather than the merely improbable.
>
>
> > It depends how the invisibility works. Maybe "unnoticeable" would be a better definition, allowing you to avoid all the issues mentioned. (But raising new ones, of course. Heh.) The invisibility would come from somehow altering the perceptions of the observer rather than the physical state of the invisible person or object. You could be looking straight at it all day - deliberately looking for it, even - but not notice it.
> >
> > Not being of scientific mind or training, I have no idea how this could be done. But I'm pretty sure *somebody* knows how to do it, because they keep doing it to my car keys.
> >
> > Brunnen-"Douglas Adams called it a Somebody Else's Problem Field"G
>
> I loved that stunt from Adams' book. If I ever knew a 92,000 foot megamountain was painted entirely in revolting day-glo pink, my brain would *definitely* edit it out of memory like a 17 mile long blind spot. :-)
>
> Speedball mentioned the old "make things invisible by bending light around them." I think this is a mainstay of so-called 23rd century Cloaking technology, which probably would use a gravity generator to alter the curvature of space, and hence cause the bending of incident light around a large object, like a ship. Larry Niven takes a different approach in another of his books, "Dream Park" I think, by using tightly-focused beams of ultrasound to create standing wave distortions in the air and therefore fade-out or "invisibilize" a person.
>
> What's even more amusing to read is Charles Berlitz's tall tale which collects a bunch of persistent rumors that in World War II, the U.S. Navy did an experiment attempting to bend light and radar waves around a ship by intense, pulsed magnetic fields. The book is called "The Philadelphia Experiment: Project Invisibility". (Berlitz is the same guy who has done "research" by writing popular science books on Atlantis and the Bermuda Triangle, etc.) Andrew Hochheimer, who has written a serious rebuttal debunking this book, describes the Invisibility project in these terms:
>
> "'Project Rainbow' was allegedly an experiment conducted upon a small destroyer escort ship in 1943 during World War II, both in the Philadelphia Naval Yard and at sea. The goal was to make that ship invisible to enemy detection. The accounts vary as to whether the original idea was to achieve invisibility to enemy radar or whether the prize sought after was more profound: *optical invisibility*. Either way, it is commonly believed that the mechanism involved was the generation of an incredibly intense magnetic field around the ship, which would cause REFRACTION or bending of light or radar waves around the ship, much like production of a heat mirage (of the sort that makes pavements reflective on hot days), which are known to be able to make islands disappear in certain conditions. The legend goes on to say that the experiment in electronic camouflage was a 'complete success'... except that the ship actually disappeared physically for a time, and then returned. They wanted to 'cloak' the ship from view, but as the story goes they got de-materialization and teleportation and crew mass insanity instead!"
>
> Wolf "Guess you can't believe everything you read" spirit

When you look at a mirage on the road on a hot summer's day, the energy from the sun (that is absorbed by the road) heats the air around it. The slight variation in the refractive index of the heated air and the unheated, or less-heated air creates the light rays to refract when they pass through the varying optical media.

As the air-heating is not consistent (being affected by wind, gravity, etc) the heat is distributed unevenly causing what looks like "ripples" in the air.

I believe that superheating the air around an object can be used to cause decreasing layers of optical density around an object, in turn bending the light to "curve" around it. Of course, this would mean that the air would have to be *extremely* hot to create such a difference, and also this would burn everything near to the object, but it is definitely a possibility.

I like what I once read on a website: "an invisible creature would be blind! Eyes work by absorbing light." I never thought of that before.